Autumn crocus: toxicity, cultivation & care

What do autumn crocuses look like? Can you grow them in your garden? Learn all about autumn crocuses and how to plant and care for them.

When the leaves begin to fall in early autumn, the autumn crocus (Colchicum autumnale) emerges and brings bright colours to the autumn scene. These purple flowers surface in open meadows and sparse forests, bringing a touch of contrast to the landscape as nature prepares for winter. You can also grow these ornamental plants in your own garden, albeit with some caution — autumn crocuses are highly poisonous. Read on to learn more interesting facts and care tips on Colchicum autumnale.

Autumn crocus: origin and characteristics

Native to Great Britain and Ireland, the autumn crocus belongs to the Colchicaceae plant family. While autumn crocus leaves and seeds first appear in spring, their flowers, as their name suggests, bloom from August to October. The solitary, six-petalled flowers are also known as “naked ladies”. Each naked ladies plant forms up to five flowers that grow upright and grouped together. Autumn crocus flowers grow to a height of 15 to 20cm.

As winter comes to an end, autumn crocuses begin sending up their 30cm-long leaves. Autumn crocus leaves are broad, elongated and thick, and curve inward slightly at the tip. With this description in mind, it is important to take special care when searching for wild garlic in spring, as there are many similarities between the two plants. Some differences are that wild garlic leaves are much thinner, often somewhat droopy, and smell strongly of garlic.

The autumn crocus’s deciduous leaves form a funnel shape. In spring, egg-shaped capsule fruits form inside the leaves’ funnel — these contain the autumn crocus’s seeds, which mature over summer. In late summer, the fruits break open and release the small, dark brown seeds, which are then dispersed by wind or ants.

By the way: like bulbous plants, autumn crocuses are geophytes, meaning they survive underground via their storage organ. Unlike the bulbs of tulips, chess flowers, crown imperials and ornamental onions, autumn crocus bulbs are botanically corms, which are formed by a thickening of the underground plant stem.

Are autumn crocuses poisonous?

Every part of an autumn crocus plant is highly toxic. Eating the leaves, tubers, flowers or seeds can be fatal. While poisoning from contact alone is unlikely, we suggest wearing gloves when handling the plant and keeping it well away from your mouth. Autumn crocuses pose a particular danger to children, as they may be drawn in by the plants. The content of the toxin colchicine continues to increase as the seeds mature and is highest in the seeds themselves. Just a few grams can kill an adult human. Autumn crocus poisoning symptoms include nausea, vomiting, circulatory failure and respiratory paralysis.

How to keep autumn crocuses in check: although autumn crocuses are toxic to humans, they are an excellent source of pollen for bees and other pollinators late in the year. However, if you are concerned about your children’s or animals’ safety, you may wish to rid your garden of these poisonous plants. The best time to get rid of autumn crocuses is in May. When their leaves emerge, cut them away at ground level. Without leaves, the plants cannot photosynthesise, so their corms will die and not be able to form new growth the following year. Always wear gloves when cutting autumn crocuses.

Autumn crocus vs crocus: what is the difference?

Autumn crocuses (Colchicum autumnale) and crocuses (Crocus) look very similar, and there is a serious risk of confusion. However, as the differences are subtle, it takes a careful eye to distinguish between the two. The following table outlines some of the distinctions.

Planting and caring for autumn crocuses

If you do wish to admire autumn crocuses in your garden, there are also white and pink cultivated forms in addition to the wild form. An especially popular variety is the double-petalled Colchicum hybrid ‘Waterlily’.

Autumn crocuses prefer sunny, wind-protected and moist locations. In their natural habitat, they like to grow among grasses, hence their tall, tubular flower stalk. Autumn crocuses feel at home in sunny open spaces as well as along semi-shaded woodland edges. They also prefer fresh to moist and nutrient-rich soil — sandy, loamy soils are ideal. Colchicum autumnale loves lime and grows well in alkaline soils.

Plant them out from July to August. For healthy growth, keep a planting distance of about 30 to 40cm between plants, equalling about five to nine plants per square metre. Place the corms 10cm-deep in the ground. If not planted deep enough, they may suffer dehydration. Autumn crocuses not only reproduce by seed but by daughter corms as well. They will reproduce via the daughter corms and eventually create an entire carpet of autumn crocus flowers in garden beds or meadows that rarely see a lawnmower.

Tip: besides the species native to the UK, many other autumn crocus species exist worldwide. Colchicum speciosum, which are more vigorous but smaller, can also find their way into our gardens. C. speciosum forms larger, fuller flowers than C. autumnales and its flowers range in colour from white to dark purple.

Autumn crocus uses

Although it makes autumn crocuses toxic, the substance colchicine is used to make some medicines, for example to treat gout. Colchicine is mainly obtained from the plant’s seeds. Colchicine is also used in plant breeding. The substance interrupts an important step in cell division, and so is used to amplify specific plant chromosome sets.

Autumn crocuses and danger to horses

Autumn crocuses are as toxic to animals as they are to humans. Even dried, the poison in autumn crocuses is still effective. Therefore, any plant leaves that are inadvertently mixed in with hay can cause problems. If ingested, horses may experience a range of poisoning symptoms, such as colic, cramps, sweating and circulatory disorders.

Before your next trip to the woods to gather wild garlic, check out our article for more information on how to tell wild garlic and autumn crocuses apart. It’s better to be safe than sorry!