Gadenin日本語Get the appTwo watering regimes, and why they cannot be swapped
The white calla is a bog plant. Its roots are adapted to airless saturated ground, it grows at the edge of standing water in the wild, and in cultivation it will sit in three to six inches (8-15 cm) of water through the whole growing season and simply get larger. Under-watering is the only serious cultural mistake you can make with it: the leaf edges brown, the whole plant shrinks and it goes dormant early, mistaking drought for the end of the season.
The colored callas grow from a tuber that spends half the year dry in the ground. Their roots rot in saturated soil, and once the bacteria that cause soft rot are inside the tuber there is nothing to be done. They want soil that is evenly moist through the growing season and freely draining, which in practice means watering thoroughly when the top inch (2.5 cm) has dried and then leaving it alone until it dries again.
The failure is nearly always in one direction. Somebody reads that callas love water, applies it to a colored tuber in a pot without drainage, and the leaves yellow from the base upward, the plant collapses and the tuber is soft when dug up. If you are unsure which kind you have, water on the cautious side and look at the leaves: broad and plain green means you can be generous, narrow and white-flecked means you cannot.
Both kinds want a mulch of two inches (5 cm) of compost around them once they are growing, kept an inch (2.5 cm) clear of the stems themselves. On the white kind it holds moisture; on the colored kinds it evens out the swing between wet and dry, which is what they actually dislike more than either extreme.
| Symptom | White calla | Colored callas |
|---|---|---|
| Leaf edges brown and dry | Not enough water; move somewhere wetter | Underwatering or scorching sun; shade at midday |
| Leaves yellowing from the base up in summer | Natural if very hot; may be going dormant early | Usually soft rot or waterlogging; dig and check the tuber |
| Whole plant collapses, base mushy and foul | Rare; crown rot in stagnant warm water | Soft rot in the tuber; lift and destroy it |
| Lush leaves, no flowers | Too much nitrogen or too much shade | Too much nitrogen; switch to high potassium |
| Leaf tips clear and dripping in the morning | Normal; the plant shedding excess water | Normal, but check that soil is not saturated |
| Pale washed-out leaf color | Hungry; feed and mulch | Too much direct sun, or hungry |
| Leaves flop in afternoon heat, recover by evening | Needs more water at the root | Normal in heat; do not add water on this alone |
Feeding for flowers rather than leaves
Callas respond to nitrogen by making leaves, and they make a great many of them at the direct expense of flowers. A plant that has been fed a general or lawn-type fertilizer produces a magnificent glossy clump with two or three flowers hidden in the middle of it, and the fix is to stop and wait rather than to feed something else on top.
The feed that suits them is a high-potassium liquid, the sort sold for tomatoes, applied every two weeks from the point where the leaves are established until flowering finishes. Potassium builds flowers and, in the colored kinds, a firmer tuber that stores better through the winter. The white calla, growing in wet ground with a heavy appetite, can take a generous dose; the colored kinds do better on the dilute side.
Do not feed a colored calla that is showing any sign of distress. Yellowing lower leaves on a colored calla are far more likely to be rot or waterlogging than hunger, and pouring feed into wet soil around a rotting tuber accelerates the loss.
- Start feeding when the leaves are fully open There is nothing to feed before that. The tuber or rhizome supplies the first flush of growth itself, and fertilizer applied to bare soil around a newly planted tuber only adds salts to the moisture around it.
- Feed every two weeks with high potassium A tomato-type liquid at the label rate for the white calla, and at half rate for the colored kinds in pots. Continue through flowering and for a few weeks after the last flower, because that is when the tuber for next year is built.
- Water first, then feed Never apply liquid feed to dry soil around a calla. Water thoroughly, wait an hour, then feed. This matters more in pots than in the ground and prevents the root scorch that shows up as sudden brown leaf margins a few days later.
- Stop feeding as the leaves start to yellow For the colored kinds this is the beginning of dormancy and continued feeding keeps them growing when they should be ripening. For the white kind in a mild climate feeding can simply ease off through the cool season and resume when growth restarts.
- Remove failing leaves cleanly Pull yellowed leaves away with a downward twist rather than cutting them halfway, or cut them right at the base. A cut stub holds water and is a way in for the same rot that takes tubers, and wearing gloves keeps the irritant sap off your hands.
Light, heat and where the plant actually wants to stand
Both kinds flower best in full sun where summers are cool, and both scorch in full sun where summers are hot and dry. The workable rule is morning sun with shade from mid-afternoon in hot climates, and as much sun as you can give them in cool ones. In deep shade either kind will grow perfectly good leaves and almost no flowers, which is a common and entirely fixable disappointment.
The white calla is more tolerant of heat than the colored kinds provided its roots are wet, because standing in water keeps it cool. The same plant in a dry border in the same heat will brown at the edges and quit. If a white calla is struggling in summer, the answer is nearly always more water rather than more shade.
The colored kinds dislike cold nights as much as they dislike heat. Below about 50F (10C) they stop growing, and a spell of cold wet weather in mid-season is when established plants sometimes rot without warning. In containers this is easy to manage by moving them; in the ground it is a reason to plant in a warm sheltered spot rather than an open exposed one.
Handling the plant safely
Every part of a calla, leaves, stems, flowers and rhizome, contains needle-like calcium oxalate crystals. Chewed, they cause immediate intense burning, swelling of the lips and tongue and, in a serious case, difficulty swallowing. This applies to people and to pets equally, and the plant is not a candidate for a bed where a small child grazes on things.
The sap also irritates skin on contact and will sting badly in a cut or in your eyes. Wear gloves for dividing, deadheading and clearing away old foliage, do not rub your face while working, and wash your hands and tools afterwards. The dropped flowers and leaves are worth clearing rather than leaving in a lawn where a dog may pick them up.
None of this makes the calla difficult to live with. It simply means treating it as a plant to look at rather than a plant to handle casually, and being deliberate on the two or three occasions a year when you do have to cut into it.
Notes worth keeping through the season
Record which kind is planted where, and next to it the watering routine you actually used. Callas repay this more than most plants because the two kinds are so easily confused after a year or two, and a note saying that the clump by the gate is the bog kind stops a colored tuber being planted next to it and drowned.
Also record the date the first flower opened and the date the leaves began to yellow. The gap between those two, and its consistency from year to year, is what tells you whether a plant is being fed and watered well after flowering or being cut short. A plant that yellows a month earlier than it did last year has usually been allowed to dry out, and the tuber you lift from it will be smaller than the one you planted.