Calla Lily Dormancy: Drying Off and Storing Colored Tubers

Which of your callas needs a rest, and why

The colored callas evolved in a climate with a hard dry season. They grow, flower, ripen their tubers and then die back completely, spending several months as a dry corky lump in dry ground with no leaves at all. That rest is not an inconvenience to be worked around; it is part of how the plant resets. A colored calla kept watered and in leaf through the winter comes into the next season exhausted, and it either flowers poorly or not at all.

The white calla is different. In a mild climate it is essentially evergreen, growing at the edge of water and continuing through winter with only a check in growth, and it needs no dry rest at all. Where summers are extremely hot and dry it may go dormant in summer instead and come back with the cool weather. Forcing a dry dormancy on a white calla is unnecessary and, if done by drying out a plant standing in water, actively harmful.

So the question of dormancy is really a question about the colored kinds. What follows applies to them, with a short note at the end about the white kind in cold regions.

Drying off is a gradual withdrawal, not a sudden stop

The instinct at the end of the season is to cut the tired foliage off and get the tuber out of the ground. Doing that costs you the tuber's size. Everything stored for next year is moved out of the leaves and down into the tuber during the weeks after flowering, and a plant cleared while its leaves are still green produces a tuber visibly smaller than the one that went in.

Instead, keep watering and feeding for four to six weeks after the last flower fades, then stop feeding and start extending the interval between waterings. The leaves will yellow of their own accord, which is the plant deciding it is finished. When at least half the foliage has gone yellow, stop watering altogether and let the rest die back dry.

In pots this is simple: move the pot somewhere sheltered from rain and leave it. In the ground it is less controllable, and in a wet autumn a bed of colored callas can be saturated exactly when the tubers want to be drying. That is a good reason to grow them in containers, and a good reason not to delay lifting once the foliage has gone over.

Cut the dead stems off about half an inch (1.2 cm) above the tuber. Do not pull them out, which tears the crown and opens the tuber to the rot that comes next.

Lifting and curing without breaking the skin

Soft rot enters a colored calla tuber through damage, and lifting is when most of the damage happens. Fork in well outside the clump, at least eight inches (20 cm) from where the stems were, and lever the whole rootball up rather than pulling at the crown. Break the soil apart with your fingers and lift the tubers out; a fork driven through the middle of a clump leaves gashes that will be soft by midwinter.

Do not wash them. Water is exactly what the curing process is removing, and washed tubers rot in storage far more often than dirty ones. Let them dry for a few days and the soil will brush off with a dry hand.

Cure them warm and airy for one to two weeks, spread in a single layer on mesh or slatted trays somewhere out of direct sun with air moving underneath. A cured tuber has a dry corky skin all over and feels light and hard. Anything still soft, weeping, sour-smelling or showing a sunken discolored patch goes in the bin, not into the box; a single rotting tuber in a closed bag will take the ones around it.

1. Lift only when the foliage has gone over Wait for at least half the leaves to yellow, then let the rest dry down. Lifting green means a smaller tuber and a poorer year to follow, and it is the commonest reason a colored calla declines steadily from a good first season.
2. Fork from well outside the clump Eight inches (20 cm) out or more, lifting the whole rootball. Every cut, gash and bruise is a door for the bacteria that liquefy the tuber over winter.
3. Cure warm and dry, do not wash Single layer, good airflow underneath, one to two weeks, out of direct sun and rain. Brush the dry soil off afterwards with your fingers rather than rinsing it.
4. Sort ruthlessly before storing Firm, dry and intact goes into the box. Soft, weeping, smelling sour, or carrying a sunken brown patch goes out. A doubtful tuber is not worth the risk to the sound ones stored beside it.
5. Store dry, dark and moderately warm Paper bags, mesh sacks or dry peat or vermiculite in an open box at 50-60F (10-16C). This is warmer than most stored bulbs want. Below about 45F (7C) the tubers suffer cold damage that shows up as failure to sprout, and sealed plastic traps moisture and rots the lot.
6. Check the box once or twice over the rest period Tip them out, look at each one and remove anything that has softened or gone moldy. Rot spreads through a stored batch quietly and the only way to catch it is to look.

Storage temperature for colored callas is not the same as for most bulbs and corms. They want 50-60F (10-16C), not just above freezing. A frost-free garage is often too cold, while a cupboard in an unheated spare room is usually about right.

The white kind, and gardens too cold to leave anything out

In a mild climate the white calla stays where it is, keeps most of its leaves and needs nothing done. A mulch of a few inches of compost over the crown in autumn is worthwhile insurance, and a clump in a pond margin can be left in the water provided the water does not freeze right down to the crown.

Where winters are genuinely cold, there are two workable approaches. Grow it in a large container and move the whole thing, still wet, into a frost-free place such as a cool porch or an unheated but protected room, keeping it just damp through the cold months. Or lift the rhizomes, cut the leaves back, and store them in barely moist compost or sawdust in the cool and the dark. The key difference from the colored kinds is that the white rhizome must not dry out completely; a rhizome allowed to shrivel in dry storage often does not recover.

Restarting is straightforward in both cases. Increase water and warmth as the days lengthen, and once the shoots are moving, resume normal treatment. For the colored tubers, bring them out after two to three months of rest, pot them up in a frost-free place a few weeks before the ground is warm enough outside, and start watering only sparingly until growth is clearly underway.

What the storage record tells you

Write down how many tubers you lifted, how many you discarded and why, and the date the foliage finished. Then compare that count against the number you planted in the spring. Colored callas that are being managed well come out of the ground more numerous and larger than they went in, since a healthy tuber gains new eyes each year; a batch that comes out smaller and fewer tells you plainly that the foliage was removed too early or the plants dried out during the growing season.

Record the storage temperature you actually achieved rather than the one you intended, and note the date you brought the tubers out of storage. Tubers stored too cold sprout late and unevenly, and matching that record against the following spring's emergence dates settles the question of whether your storage place is warm enough far more reliably than guessing at it again next autumn.