Anna Pavord: If you want colchicums to spring up in your garden at the tail-end of summer, you'll have to go to some trouble

Colchicums are dormant for such a short time, so there is only a short window when you can get hold of them to plant

Purple reign: A colchicum in full bloom (Alamy)

The rain that spoilt August Bank Holiday for so many people was only the second decent bit of rain we'd had since May. So as the water butts filled up and the trough by the greenhouse began to overflow, I wasn't complaining. The rain brought forth mushrooms (ideal conditions this season) and colchicums, the flowers pushing through the ground like fat, fleshy crocuses. They are said to like good, deep, fertile soil, ground that is well-drained but that never dries out completely, but as so often in gardening, the clump that is doing best defies the rules. It is growing in rather dry, rooty soil at the foot of a box ball.

They come always as a surprise, so fresh and new at the tail-end of summer, but because they are dormant for such a short time, there is only a short window (between late August and late September) when you can get hold of them to plant. So eager are they to push out flowers, you sometimes see them trying to do this inside the cellophane wrapping of a pre-pack. It's pathetic. So if you want some, get hold of them as soon as possible and, when planting, remember that, though they will put up with some shade, they flower most freely (and do not fall over so quickly) in an open site in full sun.

Damp meadows in the west of England were once full of wild colchicums such as C. autumnale. No longer. Environmentalists would put that down to loss of habitat. But from earliest times, colchicums (or naked ladies as they were called) were heavily collected for medicine. All parts of the plant yield the drug, colchicine, a cure for gout, as the medieval physicians of Islam discovered. But the fact that colchicums in the wild choose those kind of conditions makes growing colchicums in grass seem a good idea for those who like to garden in the wild style.

The sturdier kinds – C. autumnale and C. speciosum – will certainly survive but the problem is that you cannot mow after late August nor start again until late June the following year. The flowers come through the ground without leaves (which is why they got the name naked ladies). The foliage comes later, bossy, lush and persistent, but you can't cut it back prematurely because the leaves do the job of feeding nutrients back into the underground corm, fattening it up for the following season's performance. Unfortunately, the foliage takes up much more room than the flowers and has nothing much to recommend it.

The name of the flower comes from Colchis (an ancient kingdom – and home of all sorcery – set between the Caucasus to the north and Armenia to the south) where the first plants are said to have sprung from drops of the potion brewed by the enchantress Medea, daughter of the King of Colchis, to restore youth to her husband's father, the ageing Aeson. What power! The good news for gardeners is that deer, rabbits and mice seem to leave them alone, though you need to guard against slugs. After three or four years, you may need to lift and split overcrowded clumps. This is a job best done in late summer, before flowering begins. Replant the corms in soil refreshed with a few handfuls of bonemeal.

Colchicums are sometimes recommended for growing indoors – just set on a saucer with no soil or water. They will flower, because in the wild they are used to hot dry summers and > only produce roots after flowering, when the autumn rains begin. But unless you plant them outside as soon as they have finished their display, this artificial method of growing them will weaken the corm considerably. It may then take a season to build itself up to flowering strength again.

Corms of a colchicum such as C. speciosum can be as big as mangoes. This species won't appear in our garden till late September, following on from C. autumnale which has been out since the end of August. It's about 20cm tall and in the wild grows in the Caucasus, northeastern Turkey and Iran. The flowers, in the best forms, are taller and a much richer pink than those of C. autumnale, though they are not produced in such quantity. Usually no more than four elegantly globe-shaped blooms emerge from each corm, with orange-yellow anthers held upright in the deep greeny-white throats.

The flowers come through without leaves (Alamy)

If you have room for only one type of colchicum, this is the one to choose as the flowers are bigger and stronger than those of C. autumnale. It looks good spread under the stems of Pemberton musk roses, which produce their second flush of flowers during August and September, or planted among clumps of a fern such as Polypodium cambricum which produces its fresh fronds in late summer. The three-branched style is white, unlike the purple-topped antlers of C. autumnale. Set the corms 10cm deep and about 15cm apart.

Even more beautiful than C. speciosum is the white-flowered form 'Album', often coming into bloom later than pink-flowered C. speciosum with a very pure, delicate flower, spearing through the ground in a most surprising way. Most of the height is in the long, pale celadon-green throat which flares out into the flower. It is shy about opening up and when it does, scarcely opens enough for you to see into the centre of the flower. Everything inside is pale. The filaments carry faintly grey sacks of pollen, the stigma is divided into three thin white threads.

It is an immensely elegant thing and despite its ethereal quality, surprisingly resistant to wild autumn weather. "Cannot be equalled for beauty in the late autumn," said the Edwardian gardener, EA Bowles, one of the many who rate this the best of all colchicums. It was raised in the Yorkshire nursery of Messrs Backhouse and sold at the end of the 19th century for five guineas a bulb. Spread it in quantity round the base of shrubs such as Cotinus coggygria, or close to the low sweeping branches of Hydrangea villosa. Plant the corms 10cm deep and about 15cm apart.

Initially, when I get hold of colchicums, I plant them individually in pots of compost, covered with gravel. Set in the cold frame, protected with fine mesh netting, they can be kept safe at this stage from marauding pests. When they are safely into growth, they can be planted out in their final resting places. Then they are less likely to be dug up by wretched squirrels, which have an unerring eye for the most precious things in a garden. But colchicums are a wonderful treat in this season. They are worth any amount of trouble.

WEEKEND WORK

WHAT TO DO

* This is a good time to start preparing sites for new lawns, to be sown later in September. The earth should be well raked and all clods knocked down with a fork.

* Take cuttings of shrubs such as berberis, phlomis and potentilla. They will root most easily in a light mixture of compost and sand or vermiculite. Choose shoots that are 15-20cm long and pull them off the parent bush so each has a bit of a 'heel' (part of the older wood) attached. Bury them about 7cms deep and firm the compost down well around them.

* Cut back chives, marjoram, mint and oregano to about 7cms from the ground to encourage fresh growth that you can use during the autumn.

WHAT TO SEE

* Dahlias are at their peak this month and at style guru Nancy Lancaster's garden, Kelmarsh Hall, they are celebrating the flower with workshops and talks tomorrow and next Sunday, 28 September (11am-5pm). Admission £7.50; Kelmarsh, Northants NN6 9LY, 01604 686543, kelmarsh.com