The following information is courtesy of the Cyclamen Society
The 19 species of cyclamen vary from those hardy enough to be grown in the open ground throughout Britain and even in places with a harsher climate to those needing protection even against slight frost. Most grow robustly provided that their few simple requirements are met. A well drained growing medium is essential.
In the open garden protection from strong wind, and shade during the hottest part of the day, is usually beneficial. Under glass free ventilation is needed, but not strong draughts; shading in summer to prevent high temperatures will reduce leaf scorch and other problems.
In the open garden Cyclamen hederifolium, C.coum
and C.purpurascens grow well outside. Autumn-flowering
C. hederifolium is the easiest of all for the garden, where
it grows better than in a pot, may live to a great age, and generally
seeds itself freely. It will tolerate full sun, but tends to naturalise
rather better in dappled or part shade, as the self-sown seedlings
have a longer growing season before they go dormant. Winter-flowering
C. coum does grow well in a pot, but is very rewarding in
the garden, preferring the shadier places where the soil may be more
moist in summer. It will naturalise, too, though not always as readily
as C. hederifolium. Some special forms of C.
coum are less frost-hardy and it is wise not to risk anything
carrying an unusual name outside until you get to know it. C.
purpurascens can be awkward in pots and may be easier to satisfy in
the open ground. Essentially a woodland plant in the wild, it has been
said to prefer the open leafmouldy soil of a wood, though its main requirements
in the open are relatively still air and equable conditions. In many
parts of Britain moist shade seems the ideal. In the special case of London
and other mild gardens it does best under open sky, where it seeds itself
about, and is worth trying in shortish grass. Unusually, it is virtually
evergreen, and may flower at almost any time of year. Many other
species are well worth trying outside in most gardens. C. repandum
has been traditionally recommended for outdoors. It is generally hardy
if planted more deeply than usual, in part shade - woodland, apple trees,
tall shrubs are ideal; its subspecies are worth trying outside too. However,
many growers have now been finding more success with other species: in
rough order of "easiness", C. Cilicium, C. mirabile,
C. trochopteranthum, C.libanoticum (given perfect drainage)
C. intaminatum. Of these five, the first three will take full sun happily in the open ground, but don't mind some light shade; the others prefer a bit of shade. C. pseudibericum is less commonly tried outside than these, but where it has been tried has succeeded well, seeming to tolerate as much frost as C. cilicium. It has been a particular success in mild gardens under light woodland.
C. graecum, though ormally thought of as one of the more tender species, will survive even quite severe frosts in perfectly drained light soil, but may then lose its leaves; it does best in a sunny spot, but even then is shy-flowering in Britain and is better grown in a pot.
Planting depth is not critical. A guideline for most species in most situations is to leave about two or three centimetres (an inch or so) of soil above the tuber. C. purpurascens and C. repandum are better about ten centimetres (four inches) down. Set with some fifteen centimetres (six inches) between plants, cyclamen will quickly cover the ground. With care, pot-grown plants can be planted out at virtually any time of year. July, while the plants are dormant but thinking about coming into growth, is often an ideal planting time, and the best time to plant out seedlings. If it's been very hot and dry then, September can be excellent.
C. purpurascens is better planted in early spring, when it generally comes closest to dormancy. Pot-grown plants may be planted out at any time of year (except in severe weather), though a change of atmosphere may lose leaves. Sharp drainage is essential, especially with the deeper-planted tubers. Growers without the "perfect" site should take heart as some unlikely sites are particularly good for cyclamen - such as the tops of grit-filled walls, very steep hot dry banks, and gritty heaps of rubble. Such sites do not of course suit those species which prefer relatively shaded moist conditions.
Soil and feeding
Cyclamen will grow in most garden soils which are well drained and reasonably fertile. If this is not the case, the soil may be improved by digging in grit (for drainage), and/or leafmould, peat or other humus. If soil improvement cannot stop the ground winter, it is best to build up a raised bed, incorporating plenty of grit. If the soil is unusually acid, some lime or limestone chippings may give better growth (not necessary for C. trochopteranthum). Cyclamen often seem to grow particularly well given some root competition - anything from roses to the greedy Chamaecyparis x leylandii. Cyclamen don't normally need feeding, but some growers like to sprinkle bonemeal over the soil when growth is beginning in summer, or spread a mulch of well decomposed leafmould over the plants before growth starts. Established plants will thrive even in grass, unless this is rank, but get off to a better start if the competition is kept down by weeding. IN POTS All the species mentioned so far can usually be grown successfully in an unheated greenhouse or frame, though C. graecum and C. libanoticum are better kept frost-free. These two species, and C. balearicum, C. creticum and usually C.africanum, will stand overnight frost of up to -3 deg C (24 deg F), but should be given protection if there's a risk of more prolonged severe frost. A barely heated conservatory or cool north-facing window is better than a centrally heated room. Cyclamen species do not like the dry air of central heating; indoors their leaves can be kept turgid by giving them a daily cool "sauna" of an hour or two - just putting them in a box covered by a pane of glass. C. persicum,
C. rohlfsianum and, if it ever comes into cultivation, C. somalense must be kept frost-free. C. cyprium will stand some frost, but grows better if kept frost-free. C. parviflorum will stand any amount of cold; by contrast, the difficulty is to keep it cool under glass. It is best in a clay pot plunged to its rim in sand or even soil, with the plunge material and not the pot watered from June to October, and the plant itself watered very carefully at other times. C. graecum differs from other cyclamen in having very long strong roots which search down to the bottom of the pot. In the past this led many to grow it in a long tom type of pot, but most growers nowadays find a standard pot quite satisfactory.
C. purpurascens and C. repandum tubers are best planted deeper, with up to about ten centimetres (four inches) of compost above them. Some growers find these two woodland species difficult in pots, particularly in the temperature fluctuations of a small greenhouse - a deep plunge in sand up to the rim of the pot may help with this. C. repandum and its allies C. balearicum and C. creticum need more shade under glass than most, and do best on the floor under the shading.
Soil, pots and planting
Most specialist growers of cyclamen use clay pots; plastic ones are fine, but need more care, and restraint in watering. Cyclamen are not fussy about compost, as long as it is free-draining and not too rich. Two successful mixes are: equal parts of loam, grit/sand and peat with a dash of bonemeal; and John Innes No 1 mixed with half its volume of grit/sand. Cyclamen tend to flower better when slightly under-potted, and this also reduces the risk of overwatering. Many growers like to top the pot with two centimetres or so (3/4 inch) of coarse grit or chippings; with most species this means having the tuber showing at the top of the compost, then covering it with the layer of grit. This gives a finish which looks more attractive than compost to most people, stops mosses, algae or liverworts growing, and makes it easy to inspect the tuber if there's any suspicion of disease or insect attack (tipping off the grit for a routine summer inspection, and clearance of dead leaves and stalks, is good practice).
Watering is the most important thing to get right, particularly during the summer dormancy. Throughout the growing period plants should be watered often enough to avoid them drying out completely. Though they should not be kept damp, and never stand waterlogged, they should not be allowed to reach the point at which the leaves and stems lose their normal firmness and begin to droop.
Treatment during dormancy
In the dormant period C. persicum, C.rohlfsianum and probably
C. somalense should be allowed to dry out completely in a warm part of the greenhouse. C. africanum, C. cilicium, C. graecum, C. mirabile, C. pseudibericum and C. trochopteranthum should also be kept in a warm part during dormancy, but should get a touch of water from the base of the pot so that they are never bone-dry for long. C. balearicum, C. coum, C. creticum, C. cyprium, C. hederifolium, C. intaminatum, C. libanoticum and C. repandum should get the same watering treatment, but appreciate some summer shade. C. purpurascens needs more moisture in summer, and does best given a deep plunge, as described above. Standing clay pots on a five-centimetre (two-inch) bed of coarse sand, with the and just covering the bottom of the pots, helps to keep the temperature rather more equable than bare staging slats, and more important makes watering much easier. So long as either sand or compost makes contact through the drainage hole between sandbed and compost, the sand itself can be kept damp as a means of watering the pot - a particularly good technique during the summer dormancy period. As Summer ends, wait until new leaves appear before watering more thoroughly. The only exception to this is C. rohlfsianum : triggering it into growth by starting watering from the base in late July produces sturdier plants. Under glass, cyclamen foliage which has become accustomed to weak winter sunlight burns quickly in full spring sunshine unless there is ample cool ventilation. As few greenhouses have good enough ventilation to keep temperatures down in bright sun, in practice all species should be given shading from late March onwards, until all have gone dormant, as this will prolong their growing season. However, all but the C. repandum alliance, C. purpurascens, C. libanoticum and wholly unmarbled green-leaved forms of C. hederifolium, C. africanum and C. cyprium grow and look best if the new leaves emerge into full unlight in autumn, and stay unshaded until late March. At all times the more air they get, the better. Ventilation should be as generous as possible even in cold weather. A good flow of air, enough to shake flowers perceptibly, helps to set seed - but any icy draught will quickly kill. Cyclamen should not be sprinkled with water, though damping down sandbeds, path and staging is good in sunny weather. As flowers and leaves die, remove them immediately; keeping cyclamen scrupulously clean is the best guard against disease and some pests.
Pests and diseases
Given good cultivation, cyclamen are relatively trouble-free. Their major pests and diseases such as vine weevil and botrytis are considered in general gardening books.