Growing Hardy Ferns in Greenhouses
Hardy Ferns under Glass
It is not within the province of the section on ferns on this website, to deal with the greenhouse ferns, which need heated structures in order to keep them alive and healthy. They are a vast subject indeed, as there are many thousands of species to be considered.
On the other hand there are many coldwhich are too shady for the health of flowering plants, perhaps through near-by trees growing up and blocking the light, or perhaps through being badly placed in the shade from buildings. Such cold houses often are neglected, yet they could be made attractive and interesting by using them as homes for a collection of suitable hardy ferns.
The ideal cold greenhouse for ferns is a low-pitched lean-to, against a wall facing north or north-west, the outer wall being fixed to a low wall of brick, not more than two feet high, with hinged side lights and roof ventilators the whole length, with an earth floor, except for the path.
Guttering should be provided to lead all rain water to a tank within the house, for watering purposes, in case the public supply water is hard, and therefore unsuitable for some ferns. Hard water should not be used for watering Cryptogramma, , Gymnocarpium, Hymenophyllum, Leptopteris, Trichomanes, and Woodwardia among those species which are recommended. Hard water is harmless for damping down paths, but should not be used on indoor fern rockeries unless there is absolutely no alternative.
Staging should be provided for ferns which are to be grown in pots, and if this is fixed to the north wall, in the case of a lean-to, the rest of the house may be utilized for the formation of a fern rock garden, or some form of garden where the ferns can be planted out, because the majority of them are not happy grown in pots for any length of time; and in any case, they make better specimens when planted out.
Preferably such staging should be provided with a ledge to retain material in which the pots may be plunged, so that they do not dry out too quickly and do not require such frequent watering.
Above the stage a series of narrow troughs, eighteen to twenty-four inches above one another, should be attached to the wall. These should be six to nine inches wide and can be made by securing, with plastic-covered galvanized wire, rows of slates or tiles with their lower edges secured to the wall by resting on large nails driven into the wall, their upper edges leaning against the wires so as to form a V-shaped trough. It will be necessary to prevent the supporting wires from sagging by securing them with short lengths of wire to vine-eyes fixed in the wall.
First line the troughs with rough peat fibre, or sphagnum moss, to prevent finerwashing through; they are then to be filled up level with fern compost. In these troughs all manner of ferns can be grown if put in as young plants, and eventually they will make good specimens. Those species with pendent fronds, one or two Adiantums, Aspleniums, the hardy Davallia Mariesii and others will be suitable and gradually will provide a wall of verdure.
If the cold house is an old one, the first thing to do is to make good any weaknesses in the structure. If the glass is loose and the putty perished, it should be taken out, the bars should be scraped and painted, the glass cleaned and then replaced with fresh putty. This will eliminate any pests lurking in the cracked putty, but the house should be thoroughly disinfected, the walls scrubbed down, the water tanks emptied and cleaned out, and the staging thoroughly cleaned and repainted.
Probably the soil within the house will be poor and worn out and would better be replaced with some good top-spit fibrous loam, or rotted-down turf. The old soil should be removed to a foot’s depth and the bottom well broken up to ensure good.
If the new soil can be sterilized so much the better, as there are bound to be a great number of weed seeds and various animal pests in newly introduced soil.
If the old soil is of good texture and seems to be in good heart, it might be retained and improved by a liberal dressing of oak or beech leafmould well forked in and thoroughly mixed. Failing leafmould, spent hops well weathered may be used successfully. Peat is not a good substitute if it is very acid, as most ferns dislike an acid rooting medium, but if it must be used, a coarse fibrous or sphagnum peat is the best. Fine dusty peat is useless.
Also fork in plenty of coarse river sand, crushed brick, or stone chips. The majority of ferns like to get their roots amongst small stones.
A dressing of bonemeal, four ounces to the square yard, will provide sufficient food material for a few months.
If the house is a double-span one, and wide enough, a central bed with paths on either side, and side beds along the boundary walls, is a good arrangement. Or a central stage with side beds for planting out may be preferred. Paths alongside staging can be made quickly by the use of precast concrete flags; these are neat and easily cleaned.
In a less formal arrangement paths may be made with broken stone or clinker, surfaced with stone chippings, or crazy-paved paths may be edged with small stones over which Polypodies and the like can wander. Such paths are an attraction in themselves, and it is an easy matter to resurface them when it becomes necessary. The gravel or stone chipping paths do not get slippery or coated with algal growth, which is a distinct advantage, but they do provide a home for seedlings.
If, during part of the day, the cold house receives much sun, some kind of shading may be found necessary in order to keep the house cool. Lath blinds are the best, but they are expensive unless they can be made at home, also they need some equipment for running them up and down. This mobility is their greatest advantage: it is the work of but a few minutes to roll them up out of the way when the sun has become obscured. Scrim blinds or blinds of other light fabric mounted on rollers are excellent and can be handled manually if they are arranged to unroll along the length of the house. Their disadvantage is their relatively short life.
Light frameworks covered with laths an inch apart, as recommended in the section on cold frames, can be knocked up quickly by any handyman and they are easily laid on the glass provided the house is not too large. Permanent or semi-permanent shading by means of white or colour washes is not so good, unless the house receives strong sunlight most of the time, but it is better than none at all. If sprayed on lightly so as to pepper the glass with spots of shading, creating dappled shade, the loss of light in dull weather will not be so serious. The trouble in dull weather with shading of this type, is the absorption of too much light, resulting in weak growth and susceptibility to insect and fungal attack.
The light intensity in this country may be surprisingly high in early spring, so preparations for shading should be complete by the middle of March, and it should be removed altogether by the end of September. Lath and scrim blinds should be dried thoroughly before they are stored for the winter; this is particularly important in the case of the fabric blinds, which will rot if rolled up damp.
After shading, one of the chief requisites for successful cultivation is the provision of ample ventilation. In fact the ventilators never should be closed altogether except during gales and foggy weather, for a light airy atmosphere is essential for the well-being of most ferns; a stuffy atmosphere is to be avoided at all costs.
Although ferns like humid conditions, frequent damping down of paths is the best way to maintain atmospheric moisture. Frequent overhead spraying is detrimental to many ferns under glass, especially the Aspleniums, whose fronds may turn black and rot if kept wet continually. For the same reason watering should not be done through a rose; the water should be directed to the soil below the fronds by means of a watering can fitted with an extension spout or by an irrigation hose, a length of plastic hose with tiny holes every foot, laid between the ferns. This is, of course, for those ferns planted in the ground, but the same principles apply to the pot-grown ferns.
A rock garden for ferns under glass can be made most attractive, and will provide a home for those species which present difficulties out of doors. The method of building such a rock garden is the same as for the outdoor fern rock garden described in an earlier section, but even more care should be given to the choice of rock. This should be well-weathered natural-surfaced stone, in pieces large enough to make an effect without being too difficult to handle. Rocks of a porous nature such as millstone grit, or best of all, tufa, are the most congenial but any type of weathered rock could be used, the least useful being the granites and volcanic rocks. Weathered slate rock is charming but in general comes in too large blocks for easy handling, and it is difficult to build with and fit together. The rocks should be of such a size that they can be got through the cold house doorway. They should then be set to provide beds of varying size and levels, and vertical open joints should be left for planting those ferns which prefer these positions, such as the Spleenworts.