CULTIVATION OF HORSETAILS

By ANTHONY PIGOTT

INTRODUCTION

The Horsetails are a fascinating and attractive group of pteridophytes which are much neglected by fern growers. This article is an attempt to summarise their cultural requirements and hopefully to encourage others to begin to grow them. The author currently grows almost all the British species and hybrids, and can assure the reader that Equiseta are both easy and rewarding to cultivate.

The cultivation of Horsetails is a subject which has received little attention in the literature, and is often omitted from more general fern growing accounts. To make matters worse, such references that do exist are often inaccurate and misleading. One of the first serious references in recent years is in Manton (1950); Hoshizaki (1979) contains a more modern mention.

BASIC CULTIVATION

Containers

Any normal plant pots can be used, but should not be too small, not less than a six inch size for an established plant and as much as a twelve inch for larger vigorous ones. Pots may be either plastic or earthenware, though plastic will be more helpful in avoiding the dangers of drying out.

Large containers such as sinks and troughs may be made use of, above ground or buried to give a natural effect. The use of such containers is sometimes recommended rather than direct planting in the soil, to avoid the risk of uncontrolled spread of the rhizomes, but in practice it is only E. arvense which grows vigorously enough to become a problem to the gardener.

The rhizomes tend to grow outwards from the centre of the pot, resulting after a time in shoots crowded around the rim. Re-potting into a larger size will deal with this to some extent, but eventually it may be necessary to break up the mass of rhizomes to rearrange them to give a more even distribution of aerial shoots.

Soils, Compost & Fertilisers

Horsetails will grow in most general purpose fern composts and soils, but a good mixture to use is equal parts of loam, peat, sand and clay. Most species seem to be tolerant of a wide variety of soils, short of strongly acidic ones. However, most flourish best in the wild in situations where a mildly acidic soil is flushed by base-rich water, and so it is probably as well to bear this in mind. There appears to be no special requirements for fertilisers, other than the presence of free silica (which would be provided by a little clay), much of which is used in the aerial shoots.

Watering

It is essential that Horsetails are never allowed to dry out. This is a particularly critical problem with those grown in pots, where the rhizomes cannot reach the depth that they would if growing directly in the ground. All species need to have their rhizomes in contact with moisture, even those that appear to grow in very dry situations.

The way to deal with this vital need for water in potted plants is to stand them permanently in trays of water. A water depth of one to two inches will give a reasonable buffer against drought even in the summer months. Standing in water seems to cause no problems of rotting such as might be expected with other pteridophytes.

Light

Horsetails will grow happily in a wide range of light conditions. They seem to do best in cultivation when in strong light but short of full sun. The morphology of the plants varies with the light, those growing in full sun being somewhat bleached, stocky and less well branched, those growing in deep shade being darker green, slender and more well branched.

Shelter

Shelter is not generally important for the healthy growth of horsetails but the more fragile species, for example E. pratense and E. sylvaticum, will look better for longer if they have some protection against the wind.

PROPAGATION

Division

The simplest method of propagation is by division of the rhizomes. This is best done in the spring, just as the plant is beginning to grow. It is important to have a reasonable length of rhizome, say, six inches, preferably with good shoots starting to emerge from the rhizome joints. Newer growth towards the outside of the plant is most likely to be successful. One can often take advantage of the tendency of horsetails to send rhizomes out from the holes in the bottom of pots. If left to themselves these will usually produce roots and aerial shoots and can be detached from where they emerge from the pot. New divisions are particularly sensitive to water shortage until they become established.

From Spores

Equiseta can be grown from spores in much the same way as for ferns. Any of the usual fern spore techniques can be used but a few additional points should be borne in mind. The spores are green and are only viable for a few days in normal conditions. They have long, fine strips attached to them called 'elaters' which flex violently with even small changes in humidity. This behaviour usually makes the spores stick together as the elaters interlock, and can make it difficult to sow the spores thinly and evenly. The spores most commonly germinate in the wild on damp clayey mud; a thin layer of this on top of the usual spore mix works well but is probably not essential.

Successful germination requires good light and will even succeed in full sun (this is in contrast to the curious advice reported by Rush (1984) ). Germination is usually within a week or two but the prothalli can be rather slow growing. They seem to be particularly prone to fungal attack and so extra care must be taken in sterilisation before and after sowing.

COLLECTING & ESTABLISHMENT

The successful establishment of horsetails taken from the wild can be a very difficult task. The author originally had many frustrating attempts before the right method was found. The problem stems from the fact that horsetails usually send their rhizomes down very deep and the thin sections likely to be dug up close to the surface may have very little root and hence not be able to sustain themselves and any aerial shoots attached. Digging up sufficiently deep rhizome can be very difficult, especially in the stony, clayey soils in which they often grow.

The first step is to dig up as deep a length of rhizome as possible, looking for new shoots and buds at the joints (as when making divisions in cultivation). If the horsetail is growing in a stream, this can make it much easier to tease out a good length of rhizome. One has to be something of an opportunist, taking advantage of any fortuitous help such as rhizomes disturbed by deep ploughing or emerging from the sides of newly cut ditches. Anyone having intentions towards E. telmateia should take a strong spade (a JCB would be useful!).

Having acquired a good piece of rhizome, preferably without too much in the way of aerial shoots, it must be protected against drying out by sealing in a plastic bag. The plant should be potted in the usual way and then the pot stood in a suitable container of water right up to the rim of the pot. The depth of water is necessary to give a good chance of success. The newly transplanted horsetail should be kept like this until there are clear signs of establishment and new growth. There seems to be no problems of rot as one might expect from this treatment.

Once established, horsetails will usually grow quite strongly and cone readily. (Unlike the findings in Duckett (1970), the author's experience is that almost all species cone within one to two years of being transplanted.)

All the usual considerations concerning collecting from the wild naturally apply and should be borne in mind; however, it is difficult to imagine any of the commoner horsetails being threatened by the collection of small pieces of rhizome.

References:

DUCKETT, J.G., 1970. The Coning Behaviour of the Genus Equisetum in Britain. Brit. Fern Gaz., 10 (3): 107-112.

HOSHIZAKI, Barbara Joe, 1979. Fern Growers Manual Alfred A. Knopf, New York.

MANTON, I., 1950. Problems of cytology and evolution of the Pteridophyta. Cambridge University Press.

RUSH, Richard, 1984. Raising Pteridophytes from Spores: the Special Cases. Pteridologist 1, 3- 7.