Colchicum autumnale, commonly called the fall crocus has one of the most unusual life cycles of any plant in my garden. It flowers with no leaves and it’s seeds are stored underground for part of the year. In a given gardening season it flowers first, then rests, and then makes leaves. This is one mixed up plant that has developed a very unique and interesting life cycle.
When should you move the corms – they are not bulbs? When can you collect the seed? Important information like this becomes clear once you understand how Colchicum autumnale grows – their life cycle.
Colchicum Autumnale – The Basics
Colchicum autumnale is the most common colchicum in gardens and is also known by the common names naked lady, meadow saffron, wonder bulb, naked boy and mysteria . There are about 160 Cholchicum species and all would be great plants to grow, but they are not common in the trade.
I have written about the general culture of Colchicum autumnale as one of my favorite plants. In this post I will focus on describing the life cycle in a chronological order so that you can better understand the changes that take place during the year.
The reference to months in the subheadings is approximate and mostly refers to the climate in their native home, which is around zone 6. The date references on the pictures are from my zone 5 garden.
July and August – Dormancy
By July the plant has gone dormant. There is no visible sign above ground, and the roots have died off. This is the best time to move them and it would be the best time to buy new ones except that nurseries don’t sell them at this time of year.
September and October – Growth Begins
Starting in September, Colchicum autumnale corms become very active. A new flowering shoot develops and heads for the surface. The flowers appear above ground before any root development takes place, so all of the energy needed to develop the flowers comes from the mother corm.
Flowers are produced in succession over several weeks. Unlike other plants where the flower bud is located at the top of a flower stem, colchicums have no visible flower stem. The petals form a cone shaped organ called the corolla tube or perianth tube that originates below the surface of the soil. The pistil and stamens are formed near the top of the petals and are quite visible. The ovary is located underground at the base of the corolla tube.
This design of the flowering parts means that the seeds start to develop underground. In fact the seeds stay underground and continue to develop all winter long.
The daughter corm starts growth now and will eventually replace the mother corm.
The first roots start to show around the first of October in their natural habitat and they form on the daughter corm, not the mother corm. At first this seems odd, but the function of the roots is to supply water and nutrients to both the future developing leaves and the developing daughter corm. The old mother corm has no need for roots.
Since roots start forming late September in zone 5 it is a good idea to move and plant them before this date. If planted later, the root tips will be damaged and slow down development.
I believe the new growth (blue arrow) is the start of the leaves for next spring.
November and December – Leaves Develop
Root development continues, providing a source of water and nutrients for further plant growth. Flowering is normally finished by November.
Leaves start to develop as well, but they only grow to a point where they are just below the surface of the soil.
Almost all of the growth that has taken place so far has used the stored starch and other chemicals in the mother corm. This corm starts to shrink in size as its reserves are used up.
January and February – It’s Winter
Roots are still active and there are chemical changes taking place below ground. Everything is getting ready for spring.
March and April – Leaves Finally Show
As soon as the soil starts to warm up, the leaves start to grow. Remember they have been hiding just below the surface of the soil so that they can reach sun as quickly as possible in spring. In their native land they grow in meadows and this early start helps them grow before grasses and other plants produce too much shade.
The food reserves in the mother corm are used to expand and grow the new leaves. The leaves start photosynthesis and send the food produced to the daughter corm. The mother corm continues to reduce in size, while the daughter corm grows.
Roots are now very active, providing the water and nutrients needed by the large leaves. For such a small corm they really are huge.
One of the most surprising things for me is that as the leaves get taller, the stem holding the seed capsule also grows. Soon the seed capsule can be seen inside the bunch of leaves.
May and June – Things Slow Down
Many of the nutrients in the leaves, especially nitrogen, are sent to the daughter corm as the leaves turn yellow and die back. The mother corm continues to shrink, its role is now complete.
By early May the roots are no longer needed and they start to die off.
The seeds continue their ripening process, becoming fully ripe in early July.
In June, new buds are starting to form which will become the new daughter corms in the following year.
By the end of June the growing cycle is complete. Seeds have been produced and daughter corms are developed and full of food. It is time to take a summer rest.
The mother corm is responsible for growing roots, flowers and leaves. This requires a lot of stored energy and the most common form of this energy is starch. It is interesting to see how starch levels change over time. The following diagram, from The Role of the Roots in the Life Strategy of Colchicum autumnale, ref 1, shows how starch levels change during the season in both mother and daughter.
During rest in August, the old mother corm has a maximum of starch stored up. As flowers expand in fall the starch level drops. During winter and spring starch moves from the mother corm to the daughter corm as it continues development. In spring, the leaves finally develop above ground and replenish the total starch stored in the corms. By June the old mother corm is completely used up and the daughter corm is fully charged, ready to become next years mother corm.
Vegetative Reproduction in Colchicum Autumnale
The above description illustrates how daughter corms take over the role of mother corms to carry on the life of the plant. In order to keep the discussion simple I made no mention of vegetative reproduction – the formation of new baby corms.
Mature plants that have reached the optimal depth and have enough starch stored will start the vegetative process. The mother corm develops extra buds which can develop into secondary corms either in the fall or spring. These corms also have their own roots, and will start to develop separately from the normal mother and daughter corms, acting much like seedlings. After a year or so they will separate and become a new mother corm that continues the cycle described above.
The picture above shows a small baby corm that was removed from the mother corm in order to get a better picture.
A mother corm may also develop two regular daughter corms, both of which will develop a flower spike, as shown in the photo below. Each daughter corm has its own set of roots, and will develop its own set of leaves.
Colchicum autumnale roots have a property that many other bulbs also possess, called contractile roots. These roots function somewhat like springs. They can grow straight down and then contract like a spring, pulling the corm lower in the soil. These roots allow the corm to position itself at the best depth.
If you think about it, these are necessary. Seeds fall on the surface of the soil and germinate there. Small seedlings are fine growing at a shallow depth, but as the seasons pass, the seedling makes a larger and larger corm. These larger corms are better protected deeper in the soil. How do they get there? Contractile roots pull them deeper.
These roots can pull the corm deeper by about 1 cm/yr. Since mature corms in their native habitats live at 15 – 20 cm deep, it takes a seedling 15 years to reach the optimum depth.
From a gardeners perspective, this is useful information. It does not really matter how deep you plant the corms you buy. They will move to the depth they like which depends on climate and soil conditions.
- The Role of the Roots in the Life Strategy of Colchicum autumnale; http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.575.6298&rep=rep1&type=pdf
- Colchicum posts by Cold Climate Gardening; http://www.coldclimategardening.com/category/plant-info/colchicums/