Crocus

Light and exposure

Crocus wants sun, or at least good light. Its cup shaped flowers open wide the moment the sun touches them and close again in the evening, on a cloudy day, or even when a passing cloud blocks the light. Plant it in full sun if you want flowers wide open rather than shyly half closed.

It also does well under deciduous trees and shrubs, a rose, an apple tree, a maple, since it flowers and finishes its cycle before the canopy closes overhead and casts shade. It is one of the few bulbs that makes full use of the light under trees that would be far too shady for almost anything else once summer arrives.

Watering

Once the corms are in the ground in autumn, watering only helps if the soil is genuinely dry at planting time, to get rooting started before the first cold snap. After that, the rain of the cold season and of spring is more than enough, crocus never needs watering while it flowers.

The real risk is not too little water but too much. Once the leaves have died back, the corm goes into summer dormancy and hates sitting in soggy soil. If you grow crocus in pots or containers, let the compost dry out fully through the summer, watering it needlessly at that stage rots the corms faster than any pest would.

Soil and repotting

Crocus is not fussy, ordinary garden soil suits it fine, even poor or stony ground, as long as it drains well. It is equally happy in chalky or neutral soil.

What it cannot cope with is standing water. In heavy clay soil, break the ground up deeply and work coarse sand or fine gravel into the bottom of the planting hole, so the corms are not sitting in damp ground through their summer rest.

Temperature and humidity

Crocus is a thoroughly hardy plant: the spring crocuses take frosts of -25 to -30 °C, which means USDA zones 3 to 8, and need no winter protection at all, neither fleece nor thick mulch. In fact it is winter cold that triggers their flowering as dormancy ends.

That need for cold explains why crocus is always planted in autumn and never in spring, it needs several months of cold soil, in the order of three months below 9 °C, to prepare its flowering. A mild winter with no real cold spell often gives a more strung out, less generous display than a proper one, and in the warmest climates the corms are chilled before planting.

Pruning and upkeep

There is no real pruning to speak of. The one essential step, and the most often ignored, is letting the foliage die back completely on its own after flowering, over six to eight weeks. It is during this time that the leaves rebuild the corm’s reserves for next year’s flowers.

Never tie the leaves up and never cut them back early, even if they start to look a bit untidy among the other spring plantings. You can deadhead the spent flowers if you prefer a tidier look, but it is not necessary, crocus barely self seeds in a maintained garden.

Pests and diseases

Crocus is one of the healthiest bulbs in the garden, it has hardly any serious disease. The one fungal problem to watch for is corm rot in soil that stays too wet through the summer, easily avoided with good drainage.

The real enemy of crocus is rodents. Field mice, voles and sometimes squirrels love freshly planted corms and can clear a whole bed in a few autumn nights. Fine mesh laid at the bottom of the planting hole, or planting in a wire basket, solves the problem. Sparrows and other small birds sometimes peck at the yellow petals in spring too, an unsightly but harmless nuisance.

Propagation

Crocus multiplies entirely on its own, with no help needed. Each corm produces small offset corms around it every year, and the clump naturally grows year after year into dense, generous colonies.

If a clump gets too crowded and flowers less well, dig it up and divide the corms in late spring, once the foliage has fully died back, then replant straight away or store them dry until autumn. Growing from seed is also possible but takes three to four years before the first flower, a method for patient gardeners or amateur botanists.

Month-by-month care calendar

Green Hub tips

• Scatter crocus corms loosely across the lawn rather than planting them in straight rows for a natural look, and always wait until the foliage has turned fully yellow before the first spring mow.
• Protect freshly planted corms with a layer of fine buried mesh if field mice or voles are a problem in your garden, they can strip an entire planting overnight.
• Never confuse autumn crocus or saffron with meadow saffron. The latter looks similar from a distance but is a highly toxic plant that does not belong to the same genus at all.
• Always plant in dense groups of at least twenty corms rather than scattering single corms, the visual effect at the end of winter is not even comparable.