Caladium bulbs are more accurately referred to as corms or tubers. Small buds form from the tuber, which are the source of leaf growth. Caladium tubers can suffer rot from over-watering and from cold temperatures, among other factors. Follow these suggestions to prevent your caladium tubers from rotting.
Before the Growing Season
If you have acquired caladium bulbs several weeks before you can plant them in your garden, store them in their original shipping material at room temperature, above 70 degrees F. (21 C.) Air temperatures below 50 degrees F. (15 C.) will send them into dormancy, and they may not germinate and grow in the spring. Never store caladium bulbs in the refrigerator. Check them for bacterial and fungal infections before planting. Bacterial disease turns the outer coating of the bulbs slimy and soft, while fungus creates a dusty, brittle coating on the bulbs. If your bulbs have either of these conditions, discard them and obtain healthy bulbs.
During the Growing Season
Plant the caladium bulbs very shallowly in the soil, so they get adequate air flow and drainage. Ensure the soil temperature is well into the high 60s F. (18-20 C.), usually into May in most growing zones. Cooler temperatures will cause the caladium bulb to rot. Use a moist, rich soil that has a balanced clay and sand content to facilitate drainage. Test the soil pH before planting caladium bulbs, as they prefer a less acid soil than other plants. Soil that is too acid will also induce bulb rotting. Water as the soil becomes dry. Avoid over-watering to prevent root rot, which can allow fungus-based disease to proliferate in your caladium bulbs. Water a little every day just around the roots during hot summer weather. Avoid direct sunlight conditions for most caladiums, as the leaves will scorch and turn brown. Add a dried pine bark mulch to keep the soil moist and maintain a steady pH level. Fertilize caladium bulbs at the start of the growing season with a fertilizer in an 8-8-8 formula. During the time of peak leaf growth, use a 5-10-10 balanced fertilizer with lower nitrogen and higher phosphorus once a month. Water plants immediately afterward on the leaves and at roots to avert fertilizer burn.
After the Growing Season
Caladium bulbs are described as tender perennials, that can be stricken down at the first frost. The leaves will begin to lose color as the soil temperature falls below 55 degrees F. (12 C.). At that time, remove the bulbs from the garden and prepare them for overwintering indoors. Dry the caladium bulbs indoors at room temperature. Cut off all leaf growth from the bulbs, and pack them in a bed of dry moss. Treat them with a powdered fungicide to prevent mold-based disease and decomposition from rot. Store them away from all direct light sources at 70 degrees F (21 C.) for the fall and winter months.
Caladium bulbs, when handled with care, will resist rotting throughout the year, enabling you to replant them for several years in your garden.