Cultivation of Giant Horsetails
(see
also
www.equisetum.org
for general
discussion of horsetail cultivation)
Introduction
There are important scientific, conservation,
educational, and aesthetic reasons for introducing highly
unusual and underappreciated plants, such as giant horsetails,
into cultivation. From a scientific standpoint,
such unusual plants are likely have unusual physiological and
morphological characteristics that can be experimentally studied
and manipulated in cultivation to give us a better understanding
of the Plant Kingdom. From a conservation standpoint, plants
brought into cultivation, especially those from unique and
isolated wild populations, constitute a "hedge" against possible
destruction of the wild parent population. This helps
to ensure that the genetic resources of the original population
will not be completely lost to humankind should this population
disappear. Furthermore, cultivation of plants of
different provenances can provide much information about the
functional genetic diversity (i.e. diversity in form and physiology)
within a species and can further guard against loss of wild
populations due to human encroachment or environmental stochasticity.
With their extraordinarily primeval appearance, giant horsetails
also have great potential to inspire children and adults to learn
about the past and present diversity of plant life. Aesthetically,
the giant horsetails, and especially exceptionally robust and
regularly- branched giant horsetails like those from northern Chile, have a strikingly
beautiful symmetry.
Unfortunately, many of the giant
horsetail clones currently in cultivation lack
provenance information and do not appear to be
from the most impressive wild populations (Chad Husby,
personal observation). Hopefully the information provided
on this website will encourage botanical gardens, researchers,
and horticulturists to to seek out exceptional populations
of giant Equisetum for study and cultivation and
to record accurate provenance information for these understudied
plants.
I have been growing giant horsetails indoors
under lights and in greenhouses for several
years. I currently have two positively identified clones of
Equisetum giganteum (a clone
from Jamaica, collected by Richard Moyroud, and several
clones I recently collected in northern Chile), two
clones of E. myriochaetum
(one from the
University of California Botanical Garden
, obtained by them from a nursery
in Veracruz State, Mexico and one from the Royal Botanic Garden Edinburgh).
I also have several clones that I have not yet positively identified.
Growing these plants has been a very rewarding experience
both horticulturally and scientifically. My experiences
have allowed me to make several rather interesting observations
about the biology
of these remarkable plants. Unfortunately,
because my growing space has been very limited until recently
(both in area and height) my plants have not been able to reach large
size or normal upright form. However, I currently have
transplanted divisions of my plants to larger containers in the research greenhouse
at Florida International Univeristy. I would be very interested
to hear from others who can share their experiences
and observations with growing these plants.
Plants currently in cultivation
Several botanical gardens and university
teaching greenhouses in the temperate northern
hemisphere also grow giant horsetails for their botanical
uniqueness and primeval appearance. I am
less familiar with the extent to which giant horsetails are
grown in the tropics and the southern hemisphere.
Equisetum myriochaetum appears to be
by far the most common species in cultivation in the temperate
northern hemisphere. Although many plants in cultivation
are labeled E. giganteum , these often turn
out to be misidentified E. myriochaetum ( Moyroud, 1991
; Husby, personal observation).
For example, many of the plants labeled E.
giganteum in U.S. botanical gardens appear
to be divisions of a clone of E. myriochaetum that
was collected in Ecuador in 1987 and brought to the
University of California
Botanic Garden . Until recently,
this clone was labeled as E. giganteum . In
early 2001, Dr. Alan R. Smith determined that the clone
is actually E. myriochaetum . (Holly Forbes, 2002,
personal communication). For more discussion of misidentification
of giant horsetails, please refer to the Notes and Observations
page. Until
recently, the only positively identified E. giganteum
clone being cultivated in the northern hemisphere was
a clone collected in Jamaica by Richard Moyroud ( 1991
). I have recently brough Equisetum giganteum from northern Chile into
cultivation for research. The botanical gardens growing
positively identified E. myriochaetum
clones include the New
York Botanical Garden and The
University of California
Botanic Garden
1
. There is a clone being grown at the
Royal Botanic Garden Edinburgh
that was collected in Peru and is labeled as E.
giganteum. However, I received a division of this clone and I am
fairly confident that it is actually E. x schaffneri (the plant has
stomata in bands of 1-2 and irregular branch ridge tubercles). The
Missouri Botanical
Garden once
had a clone of E. x schaffneri in cultivation
that was collected by Dr. Richard Hauke (presumably
in Costa Rica). However, this clone eventually
died. There was a clone on the campus of
the University of Hawaii labelled
E. x schaffneri
, but this plant may no longer
exist (Dr. Gerald D. Carr, personal communication).
The plants currently in cultivation exhibit a considerable
range in vigor and regularity of branching. Richard
Moyroud ( 1991
) cultivated four clones of E.
myriochaetum from botanical gardens (two
of which were originally labeled E. giganteum
) in South Florida. He found that only
two clones grew well, one of which was not very tall or regularly
branched. In contrast, a Mexican clone of E. myriochaetum
that is being grown by the University of California Botanical
Garden (and now myself) exhibits very regular branching in cultivation
(see
photo
of a stem of this plant). Mr.
Moyroud has grown a clone of E. giganteum
collected in Jamaica and found the clone to have relatively
little vigor and irregular branching habit. I am
currently growing this Jamaican E. giganetum
clone outdoors and in a greenhouse and have found that, although
it can grow relatively well under the right conidtions (though not
as vigorously as some other giant horsetail clones), its branching
habit is markedly irregular. During my investigations of herbarium
collections, I have seen both well-branched and poorly-branched
specimens from Jamaica, so there are probably other Jamaican
E. giganteum populations likely exhibit more
regular branching habits. The E. giganteum
(presumably) populations
along the road between Moyobamba and Tarapoto
Peru exhibit highly regular branching along almost
the whole length of their stems, as do the more robust
populations in northern Chile
. Many of the most impressive E. myriochaetum
herbarium
specimens that I have seen
have been from Chiapas State, Mexico and Guatemala. The
most impressive E. giganteum specimens and photos
I have seen have been from northern
Chile . Unfortunately, the
exceptional plants from most of these areas are not in
cultivation, although I have recently brought plants from Chile into cultivation.
Hopefully, more giant horsetails with exceptionally large,
vigorous, and regularly branched stems will eventually be
introduced into cultivation so that we can learn more about
the biology of these amazing plants and enjoy their strikingly
beautiful and primeval symmetry.
Cultivation
practices
& considerations
A. Collection and propagation
(see also the discussion by Piggott, 2001
)
1. Vegetative
Propagation
Although I have not personally collected giant
horsetails from the wild for cultivation purposes, I
have experience propagating cultivated plants and I have
successfully collected living material of several temperate
Equisetum species. It is generally easy
to propagate container-grown Equisetum species
by simple division. Obtaining sufficiently long rhizome
pieces from wild populations for propagation can be more
difficult.
a.) Rhizome divisions
Fortunately, because Equiseta are
rhizomatous plants, one can usually collect propagules
from a wild population without harming it. When one
carefully collects a few modest rhizome sections from
even a relatively small clone, there generally remains much
more rhizome for continued survival and growth. Large
clones will be virtually unaffected by removal of a few
rhizome divisions. It is best to refrain from collecting
from a very small clone. I have found rhizomes (preferably
with some visible buds at some nodes) to be the most reliable
propagative material to collect. However, hard or rocky
soil and the deep-seated rhizomes of many species can make it difficult
to collect adequate lengths of rhizome. If possible, it
is generally easiest to collect rhizomes from soft, water-saturated
soil using a spade and/or a long knife to sever rhizome pieces.
Rhizomes exposed by river erosion or growing out of the
side of a bank are especially convenient for collection.
Longer rhizome sections with multiple nodes
are preferable because they have more buds and more energy reserves
for new growth than do shorter pieces. In addition, rhizomes
growing in non-saturated soil appear to be harder and more resistant to decay
than those growing in saturated soil. Therefore, rhizomes growing above
the saturated soil layers are generally more promising propagules than rhizomes
growing submerged in water or saturated soil.
I generally cut off the tops of any stems attached
to the rhizomes so that only part of the unbranched lower portions of
the stems remain attached. If too much stem is attached to
the rhizome, this could have an excessive drying effect (via transipration
from the stem) on the rhizomes before new roots develop. Aboveground
and belowground stem segments can also be used for propagation ( see below
).
It is crucial that collected rhizomes and stems
not be allowed to dry or overheat. For collecting
containers, I like to use either ziploc bags or rigid
plasic containers containing moist paper towels. The
containers should have some openings large enough to allow
air circulation (and prevent excessive heat buildup in the
sun), but at the same time maintain high humidity around the
propagules. The collecting containers should be kept
shaded as much as possible to prevent heat buildup. As
with most vegetative propagules, Equisetum rhizome cuttings should
be kept relatively cool, if possible, to reduce respiration rates
and thus conserve their internal energy reserves.
Of course, it is best to plant propagules as
soon as possible after collection. I plant
rhizomes in relatively deep containers filled with a substrate
that holds much moisture, has high capillary wicking
capacity, and is well aerated (I find commercial soilless
sphagum peat/perlite/vermiculte mixes, such as ProMix®
or Sunshine Mix®, to work well). I plant the rhizomes
horizontally ~1-2 cm deep in the substrate (with ~10-12
cm of substrate beneath the planted rhizome) to ensure ample
moisture and aeration around the rhizomes. (Please see
advantages
under "Moisture" below for discussion
of why adequate aeration is important even for these
wetland plants.) Crucially, the substrate must
be be kept constantly moist (but preferably not saturated) around
the rhizomes while they sprout new roots and stems. Below
I discuss three possible methods for maintaining
moisture levels.
b.) Aboveground
stem cuttings
Aboveground
stem cuttings (either from the main stems or from
branches) of giant horsetails can also be used to start
new plants. This is because all Equiseta
have preformed root and shoot bud primordia ( photo
of an emerging adventitious root below a branch bud of
E. giganteum
) at each node (
Gifford and Foster, 1988
). Indeed, many temperate Equisetum
species have been successfully propagated by
stem and branch cuttings (Schaffner,
1931 ; Praeger, 1934
). Although I have
successfully propagated E. giganteum,
E. myriochaetum, and E. x schaffneri from aboveground stem
cuttings, I have found aboveground stem propagules to be
less reliable than rhizome
propagules, aboveground/belowground stem cuttings,
or layering. Equisetum myriochaetum
and E. x schaffneri appear to be perhaps easier
to propagate via this method than E. giganteum
. However, my experience so far is limited to a few
clones. Cuttings from mature stems nearer the stem base appear
more satisfactory because more dormant stem buds are present
in this region, not having already developed into lateral branches.
Longer stem cuttings with multiple nodes are more likely
to successfully establish. Lateral branches can also be used,
but I have found that these thinner cuttings may have a greater
tendency to rot before becoming established. Stem cuttings
retain a definite polarity after being detached from the parent plant
in that new roots and stems extend more readily from proximal nodes than
from distal nodes.
Stem cuttings must be kept constantly moist and are
extrememly sensitive to any degree of water shortage. However,
cuttings are also very sensitive to lack of oxygen and stagnant
water. My experiments suggest that
Aero-hydroponics can be a useful system for
propagation of giant Equisetum stem
cuttings because it provides
maximally aerated
water for the cuttings. This method helps to retard stem rotting
(even for small branch cuttings) and to stimulate rapid emergence
of adventitous roots and new shoots at the cutting nodes. More
simply, one can root the stems by floating them horizontally
in water, but it is important that the water be circulated
and aerated to maintain adequate oxygen levels and prevent
stagnation because this often leads to rotting (airstones or
an aquarium pump can be used). In addition, I find
it beneficial to use opaque-sided containers and grow aquatic
plants, (especially floating plants like Lemna
, Salvinia , Pistia, and Azolla
) in the water to discourage algae growth. This "floating
stem" propagation technique was inspired by Wagner and Hammitt
( 1970
), who observed natural proliferation of severed stems of
Equisetum hyemale floating on a pond. I
suspect that partially immersing stems vertically
in containers of water (preferably with aeration and circulation)
would also work well because this technique was successfuly
used by Schaffner (1938
) to root E. hyemale
stem cuttings. Miguel Porto
(2000, personal communication) has successfully propagated
giant horsetail stem cuttings by keeping them between pieces
of moist paper under fluorescent lights. This method
helps to maintain moisture and aeration but requires special
vigilance because the paper must be regularly misted to prevent it
from drying out. Alternatively, one can plant stem cuttings
horizontally in a moist and well-aerated solid substrate (like
a soilless mix of peat and perlite). After one has stimulated
stem cuttings to form new roots and shoots by one of these methods,
the cuttings should be planted in moist, well-aerated, substrate in
a brightly lit location.
c.) Aboveground/belowground stem cuttings
My experiences with propagating Equisetum giganteum
from northern Chile have led me to conclude that one of the most effective
propagation methods is to collect aboveground/belowground stem cuttings. These
cuttings involve making a cutting composed of the unbranched lower portion
of the abovebround stem along with as much of the dark colored (and of distinctly
hardened texture) underground portion of the stem. Please refer to
this photo to
see the distinction between these aboveground and belowground portions of
an upright stem. The tough belowground portion of the aerial stem seems
quite resistant to decay and appears to contain many reserves for supporting
new root and stem growth. All my cuttings of E. giganteum of
this type have succeeded whereas many of my cuttings comprising aboveground
stems alone have failed.
d.) Layering
Giant horsetails can be successfully propagated via simple layering.
I have observed simple layering in E. giganteum in northern Chile
and I have had success with this method in cultivation. I suspect
that modified
air-layering
(without any wounding of the stem) may also
prove to be a viable stem propagation method.
Miguel Porto
and I have noticed that the preformed adventitious roots
of E. giganteum stems will begin to emerge even
on intact aerial stems when the plants are grown in a high humidity
environment. Air-layering one or more nodes of an
aerial stem would provide such a high relative humidity environment
and likely stimulate root and shoot emergence.
2. Sexual
propagation (spores)
Giant Equiseta can be successfully
propagated via spores under laboratory conditions
(using special nutrient agar, petri dishes, controlled
temperature, etc.), as reported by Hauke ( 1963
, 1969b
). However, the green spores of
Equisetum species rapidly lose their
ability to germinate (after only 5-17 days) and must
be kept in a high humidity environment to prevent dessication
( Hauke,
1963 ). Proper
temperature and light are also crucial for germination
( Hauke, 1963
). In addition,
the gametophytes are especially sensitive to fungal ( Piggott, 2001
), algal ( Hauke, 1963
), and insect larvae ( Hauke, 1969a
) contamination . These exacting requirements
limit the utility of using spores for propagation
unless it is possible to sow the spores quickly under
sterile conditions in a favorable environment. Furthermore,
ripe cones may not be present in a given population
when a collector visits it. I did not find any coning
stems in the population of E. giganteum that
I observed in Panama
. I have not yet attempted
spore propagation, but I hope to do so eventually.
B.
Growing substrate (see also related discussion
of containers
below)
I have had good success growing giant horsetails
and other Equisetum species in a standard
peat/perlite/vermiculite soilless mix (I currently
use Promix® BX) formulated for indoor, nursery, and
greenhouse plants. This substrate provides excellent
water holding capacity, ample ability to wick adequate
moisture to all levels of the 28 cm (~11 inch)
deep containers I use. Furthermore, sphagnum peat has the advantage
of providing a substantial buffering capacity for nutrients and moisture
( Whitcomb, 1988
). I have experimented with coconut coir with two Equisetum
species (E. telmateia and E. variegatum) and found this substrate
to give very poor results for even though it was of premium quality from the
purported best world source (Sri Lanka). Now, I am beginning
experiments with growing plants in the inert expanded clay aggregates commonly
used in hydroponics. When growing Equiseta in soilless
mixes, I have found that micronutrient supplementation
is often very beneficial (especially for E. giganteum
) (see discussion of mineral
nutrition below).
Richard Moyroud, a botanist and nurseryman in
Florida, successfully cultivates giant horsetails
in containers and in the ground using a strongly acidic
Florida clay. He has had good long-term success
growing an E. giganteum clone he collected in
Jamaica and an E. myriochaetum clone from the Royal
Botanic Garden Edinburgh in this substrate with no additional
fertilization.
Anthony Pigott, who maintains the United Kingdom's
National Collection of Equisetum , uses
a mix of peat substitue, loam, and clay in approximately 5:5:1
proportion. His cultivation methods are described
on his website
.
It is important to note, however,
that soil and clay vary greatly in composition and quality from one
place to another. Furthermore, soil may carry undesirable
insects or disease organisms. Hence, one needs to be careful
about the source
and preparation
of any soil to be used in a growing substrate. Some types
of soil may not have adequate micronutrients or silicon for giant
horsetails or may otherwise have properties not conducive to Equisetum
growth.
C. Moisture
Giant horsetails, like all Equiseta
, are wetland plants that absolutely require a constant
supply of moisture. Letting the potting substrate
begin to dry will result in dieback of the aerial stems
and eventually complete death of the rhizomes. On one
occassion I witnessed the rapid and permanent wilting of a
once impressive pot of E. myriochaetum that was
allowed to begin drying. Hauke ( 1966
) observed that even Equisetum arvense
, a very vigorous species that appears to
be able to grow in somewhat less moist conditions than most
others, required daily watering when grown in pots and
would "perish from irreversible wilting" if not watered
during the weekend as well as on week days. This
was despite the fact that E. arvense was the most
water-use-efficient of the three Equisetum species
( E. arvense , E. hyemale , and
) studied by Dosdall ( 1919
). Maintaining high moisture supply
is even more crucial for starting plants from rhizome
pieces and stem cuttings. There are several possible
methods for maintaining continually moist substrate conditions
and I discuss these below.
Indoors:
1. The
containers can be set in either individual trays
or a common basin with ~1-4 cm of water in the bottom so
that the potting medium is kept constantly moist by wicking
action of the substrate. This is the method that Anthony Pigott
and Richard Moyroud use and
requires the least maintenance of the methods I discuss.
This method is suitable so long as the basin
is emptied periodically and the pots are occasionally
leached by watering thoroughly from the top. This leaching
is important for preventing excess buildup of fertilizer salts
and irrigation water minerals in the substrate from evaportion.
A buildup of salts and other dissolved minerals can
be very detrimental to horsetails because this reduces the availability
of water in the substrate and may cause toxicities or nutrient uptake
imbalances. Hence, this method is particularly suited to outdoor
or greenhouse cultivation where it is convenient to use a hose to
flush out old water in the basins onto the ground. Introducing
floating plants, such as duckweed (Lemna ), Azolla,
or Salvinia to the basins of water, can prevent excess
algae from growing and also absorb some excess fertilizer salts.
Containers for use with this method must have drainage
holes on the bottom that allow water to enter the pots regardless
of the basin water level. Rhizomes will often "escape"
through drainage holes when this method is used. These
rhizomes can be used for propagation when they have grown sufficiently
long.
2. I
currently use a modification of the semi-hydroponic
TM
watering method pioneered by Ray Bark of First Ray's Orchids
. This is essentially
a compromise between methods 1 and 3 and is the method
that I have found most convenient for non-greenhouse indoor cultivation.
I use translucent plastic containers with 2-3 holes
(~5 mm diameter) drilled ~4-6 cm high on the side of each
container. I then fill the bottom part of the container
(to just above the side drainage holes) with inert clay
aggregates (medium grade,
~8-16 mm diameter) commonly used in hydroponics.
On top of the aggregates I place an ~3 cm thick layer of
long-grain sphagnum moss or coconut husk chips. Finally,
I fill the rest of the container (~15-20 cm above
the sphagnum or coconut husk layer; see discussion of containers ) with
the peat/perlite/vermiculite mix that I typically use. When
I water these containers, the part of the container below
the drainage holes serves as a water reservoir and the clay
aggregates wick water from the reservoir to the upper layers.
I can always check the water level in the containers because
they are translucent. The sphagnum or coconut chip layer
prevents the fine peat-based substrate from sifting down into
the reservoir. I set these containers on inverted pots inside
large plastic trays to catch overflow from the pot bases during watering.
With this method, it is crucial that water be available in the
reservoir at all times, so one needs to replenish the reservoir when
the water level becomes low.
Advanges of the modified Semi-hydroponic
TM method:
i.)
The main advantage of this method is that the
pots can be easily and frequently leached. To
leach the containers, one simply waters so that substantial
water overflows from the container reservoir and spills
into the catchbasin below. This prevents buildup of
fertilizer salts and tapwater minerals in the substrate and,
unlike method #1, does not require changing of the basin
water. I grow floating plants in the catchbasins to
prevent algae growth.
ii.) As
with method #1, there is no guesswork involved in
deciding when to water. For both methods, water
must be present in the reservoir at all times.
iii.) Because the clay aggregate layer is the only
layer that gets saturated with water, this method avoids
anaerobic decay of the substrate by keeping the
organic substrate above the water reservoir. I
have found that using organic substrates with method #1
results in a sour smell in the bases of the pots that can
be detected during re-potting or by smelling the base of
the pots when they are lifted out of the reservoir. This
smell results from the formation of organic acids (such as
acetic acid) and is evidence of anaerobic decay of the organic
substrate (
Armstrong and Armstrong, 2001
). Using the clay aggregate method, the
sour smell has completely disappeared from my pots, suggesting
that aerobic conditions prevail throughout the substrate.
**Note: the clay pellet layer can also be used with method
#1 to prevent souring of the lower substrate.
Researchers have shown that that organic acids
produced by decaying organic matter in saturated soil
can reduce growth, or even cause die-back, of wetland
plants such as the common reed ( Phragmites australis
Cav.) and rice (Oryza sativa L.) ( Armstrong and
Armstrong, 2001 ; 1999
;
Armstrong et al., 1996
). Furthermore, even wetland plants (that
are adapted to flooded soil conditions), grow more slowly
under highly reducing conditions caused by decaying organic
matter in saturated soil than they do under oxidizing conditions.
This phenomenon has been shown in wetland plants
such as rice (
Kludze and DeLaune, 1995
) cattail (Typha domingensis L.)
( Kludze and DeLaune, 1996
), Sawgrass (Cladium jamaicense
L.) ( Kludze
and DeLaune, 1996
), and baldcypress (Taxodium distichum L.)
(Pezeshki DeLaune, 1998
).
The clay aggregate reservoir method, allows the
grower to avoid anaerobic decomposition of the substrate
and has the added benefit of preventing buildup of rhizomes
in the saturated layer (discussed in iv
. below). Since rhizomes and roots eventually
die and decay, it seems desirable to prevent large amounts
of such dead decaying organic matter to accumulate in a water
saturated zone around healthy rhizomes and roots.
Although giant horsetails can clearly tolerate
saturated anaerobic conditions in the substrate (probably
via oxygen diffusion through the large air canals in
stems and rhizomes), I think that they are likely to do
best when provided with both constant moisture and
aerobic conditions throughout most or all of the substrate. Indeed,
my horsetails are growing more vigorously than ever using
the Semi-hydroponic TM
method. Page (
2002 ) has observed
that Equisetum species in Britain and Ireland
vary with regard to their ability to tolerate lack of
substrate water movement (and hence presumably greater anaerobiosis
in the substrate). Therefore, it seems prudent to
"err on the safe side" by providing considerable aeration
along withample moisture availability. The species
requiring the most substrate water movment (hence, presumably,
most aerobic conditions) in the British Isles is
Equisetum telmateia (Page,
2002 ).
I am having very good success growing this species
using the modified semi-hydroponic TM
method, so this method appears to provide sufficient
aeration for one of the species least tolerant of anaerobiosis.
This semi-hydroponic TM
method is also proving very satisfactory for growth
of my E. giganteum, E. myriochaetum, and E.
x schaffneri clones as well as other Equisetum species
( E. diffusum , E. variegatum ,
and E. laevigatum ). At this time
it is not clear how the anaerobiosis tolerances of the giant
horsetails compare to those of other species in the genus.
This would make a very interesting research question
(see more detailed discussion on the Ecology and Physiology
page).
When a grower uses a substrate with little or no
organic matter (such as the acid clay used by Richard
Moyroud), the problem of anaerobic substrate decay would
not be such an important issue. Anaerobic decay
would also likely be less of an issue for mixes that include
large proportions of mineral soil and/or clay in addition to
organic matter (such as the mix favored by Anthony Pigott
)
iv.) A fourth advantage
is that the layer of clay aggregates at the bottom
can discourage rhizomes from accumulating and circling
around the bottom outside edge of the pot. Once
the rhizomes reach the hard clay aggregates, they
tend to be deflected in a different direction or sometimes
simply become wedged between the aggregates and cease downward
growth (this probably stimulates branching of the rhizome
above the wedged end). Premilinary observations suggest
that this encourages the rhizomes to grow more evenly throughout
the growing media and encourages a more even filling of the
container with aerial stems than would otherwise occur ( Anthony Pigott
discusses the problem of rhizomes and shoots eventually
accumulating around the outside edges of pots).
v.)
Another advantage of this method is that the
translucent pots allow observation of rhizome and root
growth, which is quite interesting. (of course, one
could also use translucent pots with methods #1 and #3.)
Disadvanges of the modified Semi-hydroponic
TM method
i.) The main disadvantage that I have experienced
so far is that more frequent watering is
required for this method than for method #1, especialy
when plants begin to fill their pots.
ii.)
If the sides of the translucent containers receive
enough light exposure then algae will grow on the outer
layer of the potting media. This appears to be
mainly an aesthetic concern. Because I grow my plants
under overhead fluorescent lights, this has not been much
of an issue for me. However, it is more prevalent in a greenhouse
with abundant light. Using translucent containers that are tinted
blue might solve the problem by minimizing transmission
of the photosynthetically active wavelengths (see.
Soffer, 1986
).
3. The
containers can be made without any water reservoir
so long as they are watered frequently enough that the
substrate remains continually moist. This can be
accomplished either by regular hand watering or by an automated system
(such as a drip system or sprinker system). Of course, this method
leaves little margin for error.
Outdoors:
If one lives in a warm enough area to attempt growing
giant horsetails outdoors then the plants may be grown
in the ground or in containers. If the horsetails
are to be grown in the soil, then they should be planted in a
low wet area, preferably near a stream, marsh, or pond. If
no natural wet area exists on the property, then a bog can
be
constructed
for the giant horsetails using a special
liner to hold water in the upper soil layers.
If the giant horsetails are to be grown in containers,
then the same methods as those used for indoor container
cultivation can be used.
D.
Containers
i.) Type
A variety of cotainers can be successfully used for
growing giant horsetails. I favor plastic translucent
containers because they are compatible with the semi-hydroponic TM method described above and
because the translucence allows one to observe rhizome
and root growth. I prefer to buy containers without
holes so that I can drill holes to accomodate the semi-hydroponic TM method. The semi-hydroponic TM pots offered by
First Rays Orchids
work well, as do various plastic containers that can be purchased
at department stores.
ii.) Overall
size
In the past, I have successfully grown giant horsetails
in pots as small as 6 x 6 inches (15.24 x 15.24 cm). Of
course, in smaller pots, the stems will not get large and
successful division will sometimes not be as easy due to the
smaller amount of rhizome material available. Easier and faster
propagation of plants grown in larger containers is due to
the increased length of rhizomes and hence greater number of buds
and greater stored energy present in the resulting larger divisions.
Currently, I am also using rectangular plastic storage
containers of various sizes, the smallest of which are ~27 cm (~11
in.) tall, ~33 cm long (~13 in.) long, and ~18 cm (~7 in.) wide.
These containers have proven to be sufficiently large
to allow good rhizome growth and very successful division.
iii.) Depth
Container depth is a crucial consideration and,
along with substrate type, is a principal factor affecting
drainage. Contrary to popular belief, adding stones or
or other coarse objects to the bottom of a container does not
improve drainage, but using a taller container does ( Whitcomb, 1988
). This is because a container
is watered there is always a perched water table at
the bottom of the substrate column. Hence, adding coarse
components at the base of a column of a given type of substrate
merely shortens the substrate column and hence raises the perched
water table. Thus, adding coarse drainage aggregates
actually decreases the volume of well-aerated substrate, whereas
using a taller container increases the volume of well-drained
substrate above the perched water table. I have not yet
performed experiments to investigate the effects of container depth on growth
of giant horsetails.
My preferred method for growing horsetails involves
providing a substrate environment that is constantly moist
and also well-aerated. Because giant horsetails
benefit from having a substantial volume of moist substrate
available for rhizome growth, I prefer to use relatively
deep (27 cm = approx. 11 in.) containers along with a substrate
that has high wicking capability (i.e. high capillarity)
and so can wick sufficient moisture throughout the substrate
column (drawing moisture from the water reservoir in the base
of the pot). For discussion of the substrate I use, see
above
. Using deeper containers creates
a longer gradient of substrate moisture and aeration
conditions. This allows Equisetum rhizomes
and roots to seek out the most favorable growing conditions.
For more detailed discussion of container depth and
substrate type (along with helpful figures), I highly
recommend the following horticultural technical bulletins:
http://www.agf.gov.bc.ca/croplive/plant/horticult/floricul/aeration.pdf
http://envhort.ucdavis.edu/Ehweb/Newsltr/1998/GP98winter.pdf
http://www.ces.ncsu.edu/depts/hort/floriculture/plugs/ghsubfert.pdf
E.
Mineral nutrition
It is important to note
that the giant horsetails (and other Equisetum species,
for that matter) do not seem responsive to high rates of macronutrient
( N-P-K) fertilization. In fact, overfertilization is a real
danger to Equiseta. Richard Moyroud has maintained
E. myriochaetum and E. giganteum in containers
with the same acid clay substrate for about 10 years without any
supplemental fertilization. However, plants that he fertilized
heavily were almost killed by the high fertilizer levels. Similarly,
Anthony Pigott
has found that the Equiseta he grows in soil-based substrates
do not appear to require additional fertilization. High fertilizer
levels may harm giant Equiseta by lowering the osmotic potential
of the substrate water or through nutrient imbalances and toxicities.
On the other hand, I have
found that some fertilization (especially with micronutrients)
is necessary if one is using a soilless mix. When I fertilize
my Equiseta growing in soilless mixes, I use only a low-strength
solution (described below) and I do not fertilize with every watering.
I usually irrigate with a fertilizer solution at 2-4 week intervals
and irrigate with plain water in between fertilizations. I
often irrigate the plants to the point that excess water starts to
drain out of the side holes in my containers (i.e. I filll the built-in
reservoirs to overflowing). This ensures that excess fertilizer
salts (and minerals that might accumulate from evaporation of irrigation
water) are periodically flushed from the substrate. I
have also found that slow-release fertilizer sticks that include micronutrients
can be effective for use with fast-growing Equiseta in a greenhouse.
I have found that it is wise to avoid using high rates of macronutrient
fertilization and to periodically leach the substrate with plain water
to avoid overfertilization. Making sure that adequate
levels of micronutrients are available (preferably via a slow release
fertilizer or by adding some clay or mineral soil to the substrate)
often appears to be a key to successful cultivation of giant horsetails
in soilless substrates.
I use three different fertilizers to grow
Equisetum species in soilless
substrates:
1. Controlled-release micronutrient fertilization
( key to success with E. giganteum
in soilless mixes ):
For growing giant Equiseta (and
several other Equisetum species) in
soilless substrate, I have found the addition of a controlled-release
micronutrient fertilizer
is very important (especially for
E. giganteum ). Whitcomb ( 1988
) discussed studies showing the benefits of slow-release
micronutrient fertilization for growth of many containerized
woody plants in soilless mixes and like benefits accrue
to horsetails. I use Micromax ®
micronutrient fertilizer (at a low rate: 1/8 teaspoon
per volume of substrate that will loosely fill a 5" pot) with
excellent success, but other similar controlled-release micronutrient
fertilizers should also work well. Kelp-based
fertilizers may also prove to be satisfactory for providing
micronutrients (and extra potassium), although I have not yet
tried these. For giant Equisetum growers
who use soil in their substrate mixes, micronutrient fertilization
may well be unnecessary because adequate micronutrients are
likely present in the soil component. I do not know which
micronutrient(s) are most important for giant Equisetum
nutrition. However, Cannon et al. ( 1968
) found that many Equisetum species are accumulators
of zinc, so perhaps they have a high requirement for this
nutrient.
2. Macronutrient
fertilization :
I also fertilize my giant horsetails with a complete
liquid hydroponic fertilizer (Dyna-Gro
TM 7-9-5) and, in the greenhouse, with Miracle-Gro
Plant Food Spikes (6-12-6 with micronutrients). I usually use
the liquid fertilizer at the lowest recommended concentration
(1/4 teaspoon/gallon) because in my experience horsetails
appear to have rather low absolute N-P-K requirements.
The reason I use a hydroponic fertilizer is because such
fertilizers tend to contain a balance of all essential mineral
elements, including micronutrients, Calcium, Magnesium, and
Sulfur. A study of the N and K nutritition of
Equisetum arvense showed that this species has high
K requirements relative to N (
Andersson, 1999b
). If this finding also holds for
giant horsetails, then ensuring adequate K fertilization
(relative to N) will be important for maintaining good
growth and vigor.
3. Silicon
fertilization :
Horsetails are the only vascular plants known
to require silicon (Si) as an essential mineral element
( Epstein, 1999
). The requirement
for silicon has been shown for Equisetum
arvense (
Chen and Lewin, 1969
) and for E. hyemale ( Hoffman and Hillson,
1979 ), so this
requirement appears to hold for members of both subgenera
within Equisetum . An important
function of silica in Equisetum is in maintenance of shoot erectness
(Kaufman et al., 1971). Furthermore,
silica content of stems appears to be directly associated with stem
longevity (Srinivasan et al., 1979).
Horsetails incorporate much silicon into their
stem tissues and external ridges, knobs, and rosettes of silicon
give the stems of many species their rough and abrasive character
(including the rough-stemmed E. giganteum
, but to a lesser extent the smooth-stemmed E. myriochaetum
) ( Gifford and Foster,
1989 ; Hauke,
1963 ). People have
taken advantage of this abrasize quality by using
Equisetum stems for washing dishes (hence
the common names 'scouring rush' and 'limpiaplata'), polish
woodwind reeds, and polish silver (hence the name 'yerba
del platero'). The outer layer of silica on Equisetum
stems may help explain why horsetails appear to be
little bothered by insect feeding or fungal diseases ( Hauke, 1969a
; Kaufman
et al., 1971 ). Gardeners
have long used silica rich Equisetum
extracts to help protect plants against pathogens and predators
( Quarles, 1995
). For discussion of Silicon's role
in plant health, see my 1998 paper " The Role of Silicon
in Plant Susceptibility to Disease
".
Since Si levels are low in organic soilless media
and many ornamental plants and Equsetum arvense have
been shown to benefit from Si fertilization ( Chen et al., 2000
(
full text )), I add
a potassium silicate liquid fertilizer (
Pro-Tekt ®,
manufactured by Dyna-Gro TM
) to the my fertilizer solution (at the lowest
recommended rate of 1/4 teaspoon/gallon). In addition
to providing silicon, this fertilizer also adds more
K to fertilizer the solution and, as discussed above, a higher
proportion of K is probably beneficial for Equisetum
( Andersson,
1999b ). If soil or clay are included
in the growing substrate, then additional Si fertilization
may be unnecessary.
F.
Light
Giant horsetails require plenty of light and are
shade intolerant (
Hauke, 1969a
; Moyroud, 1991
). I have had good success
growing them indoors under compact fluorescent lights,
which are quite bright. I am also growing giant horsetails
with excellent success in full sun outdoors (in Florida) and in a bright
greenhouse.
G.
Humidity
In my experience, giant horsetails appear to grow
well in a wide range of humidity levels. Botanic gardens
often grow giant horsetails in humid conservatories. However,
I am growing these plants both in a humid greenhouse and
in a small air-conditioned apartment with relatively low
ambient relative humidity (RH) during the day (40-50%) and and
higher relative humidity at night (~60-75%). My giant
horsetails do quite well in both environments. Miguel Porto
reports that giant Equiseta grow well outdoors
in Portugal where the RH levels are low. However, giant horsetails
can only tolerate low RH levels when provided with
constant substrate moisture. It is also quite possible that horsetail
growth may benefit from increased RH.
H.
Temperature
Little information is available on the temperature
tolerances of giant horsetails because most plants are
grown in conservatories. Miguel Porto has reported that
his giant Equiseta from Costa Rica grew
well throughout the winter when temperatures dropped as low
as 7ºC at night. Equisetum. myriochaetum
is growing successfully outdoors in San Francisco, California
and West Palm Beach Florida, where low temperatures can
reach -1ºC. It seems likely that plants from higher elevation
populations or populations of E. giganteum
near the southern part of this species' range (central
Chile and Argentina) would be more cold tolerant. Richard
Moyroud successfully grows E. myriochaetum
(one clone) and E. giganteum (one clone)
outdoors in south Florida (with hot, humid summers and warm nights),
so some clones are heat tolerant. However, several
clones of E. myriochaetum grew relatively
poorly outdoors in South Florida and hence may have been
less heat tolerant (possibly they came from higher elevation
populations) ( Moyroud, 1991
). Warm summer night temperatures in lowland
tropical areas such as South Florida may be problematic
for high elevation giant horsetail clones as is the case for
some tropical montane bamboos. However, much experimentation
remains to be done with regard to temperature tolerances.
I.
Stem support
Individual giant horsetail stems up to 2-3 m high
and ~ 1 cm in diameter can generally support themselves ( Spatz et al.,
1998 ; Moyroud, 1991
). However, for such slender stem diameters,
taller stems require support either from neighboring
stems or other vegetation. The emarkably robust
stems of the northern Chile
populations of E. giganteum
can remain self-supporting to greater heights (Chad Husby,
personal observation).
To encourage giant horsetail stems to remain upright
in the garden, it would be helpful to plant them in
a location that is sheltered from the wind. In addition,
some sort of support (such as a fence around the plant)
can help prevent stems from falling over due to wind or due
to having grown too tall.
Other considerations
Pests
Fortunately, giant horsetails appear to have
few problems with herbivorous insects and fungal diseases
in nature (
Hauke, 1969a ). However,
on a few occassions I have observed horsetails in greenhouses
being attacked by mealybugs, aphids, and scales. Anthony Pigott has
also had insect pests on his horsetails. Plants in a greenhouse
setting may tend to be more susceptible to pests because the stems
of giant horsetails appear somewhat less hard when grown in a high
relative humidity (RH) environment than when grown in a lower RH environment.
Both Miguel Porto and myself have observed this reduction in stem
hardness or "toughness" when grown under higher RH. Furthermore,
Dayanandan et al. (1973) noted that
outdoor-grown plants of Equisetum hyemale var. affine tend
to have "heavier wax and silica depositions" on the epidermis than do
greenhouse grown plants (However, the outdoor plants the authors compared
to the greenhouse-grown plants may not have been of the same clone). This
difference may be due to the generally higher humidity levels in greenhouses
than outdoors.
Do giant horsetails grow too large for indoor
cultivation?
Although giant horsetails have the potential to
grow quite tall under favorable conditions, they can
be kept smaller by limiting the size of the growing container.
I have found that plants in a small container
will continue to produce relatively small stems. Periodic
division and replanting will also help keep stems small. If
larger stems are desired, then larger containers should be
used.
Growing these plants under artificial light presents
a challenge because most artificial light sources
need to be within ~0.5 m of the top of the planting
container to be effective. I get around this problem
by simply guiding longer stems around my compact fluorescent
light fixtures when the stems begin to grow into the
fixtures (otherwise, coming into contact with the bulbs
would kill the stem apex). Once the stems grow upwards
beyon the light source, they eventually start to curve to
the side and then downward (see discussion of phototropism
). At least in E. giganteum and E.
x schaffneri, the tall stems eventually start to become
more flexible and lay on their sides so that the whole stem
is once again exposed to light. Hence, one can grow these
plants indoors under lights, but of course this prevents the
plants from developing an attractive upright form.
Will
giant horsetails become invasive weeds?
Giant horsetails are early-successional
plants and are poor competitors that are sensitive
to being shaded by other vegetation ( Hauke, 1969a
; Øllgaard, 2000, personal communication).
In addition, the slender architecture of giant
horsetail stems causes them to cast little shade on other
plants. The one giant horsetail clone (of E. myriochaetum
) that has been successfully established outdoors in
cultivation in south Florida has spread little from its place
of planting more than 10 years ago. Furthermore, the stems
of this clone are quite sparse and clearly do not threaten
any native vegetation. Because reproduction by spores requires
very exacting conditions (see discussion of Ecology and Physiology
) and because the spores
are short lived (
Hauke, 1963 ), dispersal
by this means beyond a cultivation site is unlikely. Moyroud
( 1991
) makes the point that E. giganteum
spore from the Greater Antilles has probably "rained
into South Florida...for millennia" without establishing any lasting
presence of this species in Florida.
I am not aware of any case of a horsetail species
being an ecological problem anywhere in the world. Horsetails
in general are poor competitors and do not threaten other
vegetation. However, two species,
E. arvense and E. palustre are sometimes
agricultural weeds in temperate areas ( Holm et al., 1977
). These species, both members
of the subgenus Equisetum,
can cause health problems in livestock when the animals
consume the horsetails stems in forage for extended periods
of time (
Holm et al., 1977
). The toxin in E. arvense is a thiaminase
enzyme that eventually causes thiamine deficiency whereas
the toxin in E. palustre is an alkaloid,
palustrine (
Holm et al., 1977
). Equisetum arvense is sometimes
a weed in certain temperate crops, but only reduces
yield when present at high densities ( Parsons, 1992
). Equisetum palustre
is far less frequently reported crops than is E. arvense
(
Holm et al., 1977
). Equisetum arvense is the only
Equisetum species that has become an
agricultural weed in areas in which it is not native (such
as Argentina, Madagascar, New Zealand, and Australia) ( Parsons and Cuthbertson,
1992 ; Holm et al., 1977
). It is not surprising that E. arvense
is the only Equisetum species
to become an exotic weed because it is also the most
"weedy" member of the genus in its native area. It is
"weedy" in the sense that it is the "most common and widespread
species of the genus" (Hauke, 1966
). Anthony Pigott maintains the most comprehensive
Equisetum collection (including
every species and many varieties and hybrids) in the world
( U.K. National
Collection ). He has
found that "it is only E. arvense which grows vigorously
enough to become a problem to the gardener" (see "cultivation"
at www.equisetum.org
). However, he advises
caution regarding some of the more vigorous hybrids (such as E. x
font queri and E. x bowmanii) and suggests that these
are probably best confined to containers.
Populations of the giant Equiseta
are mostly uncommon and scattered throughout most
of their ranges (cf. Hauke, 1969a
), with the notable exceptions
(of which I am aware) of the Ecuadorian Andes (Benjamin
Øllgaard, personal communication) and the Central
Plateau and Northern Highlands of Chiapas State, Mexico ( Smith, 1981
), and several river valleys
in northern Chile (Chad Husby, personal observation). I have heard
no reports of any cultivated giant horsetail escaping
cultivation or becoming invasive. On the contrary,
I have heard from several greenhouse curators who have had
considerable difficulty growing certain giant horsetail clones.
Unlike the two weedy members of the subgenus
Equisetum , the giant horsetails do not
appear to be harmful to livestock. A recent study
revealed no acute toxicity of E. giganteum in
mice ( Gorzalczany
et al. 1999 ).
Furthermore, (
Hauke, 1969a ) reported
that many of the populations he visited were associated
with pastures and that "cattle graze upon it with apparent
relish". Indeed, Hauke ( 1969a
) mentions that one campesino "claimed that
Cola de Caballo was good for the cattle, preventing some
trouble with their blood". Because cattle ranching
is extensive in Central America (Chad Husby, personal observation),
it seems unlikely that a toxicity due to giant horsetails
would be overlooked by ranchers. Hence, it seems
likely that they pose no threat to livestock or agriculture.
No species in the subgenus Hippochaete
(to which the giant horsetails belong) is an
ecological or environmental problem anywhere. I
know of only one documented case of long-distance anthropogenic
dispersal of a member of the subgenus Hippochaete
. The European horsetail E. ramossismum
was introduced (via rhizome pieces in ship ballast)
to sites in two port cities 2
in the United States more than a century ago (Hauke, 1979 ).
However, the populations have not spread beyond their
sites of introduction and one of the populations appears
to be declining due to encroachment by woody vegetation ( Hauke, 1992
).
Horsetails in general, and the giant horsetails
in particular, do not have many associations with herbivorous
insects or pathogenic fung ( Hauke, 1969a
). This suggests that one
would not expect giant Equiseta
to become unexpectedly vigorous and invasive in a new environment
as a result of being "released" from herbivores and diseases
that suppressed the plants in their native environments.
Some biologists studying invasive species believe that
the "release effect" is often a significant factor in plant
invasions. Experience so far has borne out the hypothesis
that a "release effect" is not to be expected for horsetails
cultivated in new locations. As discussed above, even
after more than 100 years E. ramosissimum has
failed to spread from its sites of introduction in the United States
and this temperate European species is better adapted to the climate
of the United States mainland than are the giant horsetails. Furthermore,
after 10 years outdoors in South Florida E. myriochaetum
has shown no propensity to spread from its sites of
cultivation or to compete with native vegetation. Indeed,
with the exception of E. arvense , the few Equiseta
that have been introduced into new places appear to grow
less well than in their native environments.
The giant horsetails, being memebers of the subgenus
Hippochaete , do not appear to be potential
invasive ecological or agricultural weeds when cultivated
as ornamental plants. Experience so far suggests
that the real challenge will be to find ways to encourage
them to grow large and dense in garden settings while preventing
other vegetation from choking them out.
1. Although the University of California
Botanical Garden lists E. giganteum in
its collections database, in 2001
Dr. Alan R. Smith determined that this plant is actually
E. myiochaetum (Holly Forbes, personal
communication, 2002).
2. The
cities are: Pensacola, Florida and Wilmington,
Delaware.
