Keep These Children Warm
These are tropical plants who resent temperatures below 65ºF (18ºC). Once the tubers are injured by cold, the damage is irreversible. You may not see it immediately, but cold causes the tissues to die, so you really have to be careful about temperatures with these plants.
Whether or not they get damaged depends not only on the temperature but on how long they are exposed to it. If they get damaged by cold, they will be slower to sprout (if at all), have fewer leaves and not grow as well.
If you buy dormant tubers, make sure they are firm to the touch. Rubbery feeling tubers indicate cold damage. Be careful buying plants or tubers from the big box stores who often display them too early in spring, in outside displays, where they can be subject to cold temperatures for too long for their subsequent health.
Planting
You can grow caladiums in pots or in the ground. They will not be hardy for you unless you garden in south central Florida or the southernmost part of Texas. If you grow them in the ground, you will need to lift them when day temperatures hit the mid 60s (18sC) or treat them as expensive annuals and replace them each year. Growing them in pots is the easiest way to keep the same tubers going for many years. The most important element (other than temperature) is moisture. If you let them dry out to the wilting point, they will go dormant. Once dormant, it takes them a goodish while to wake up again.
If you grow in pots, your potting soil should contain enough peat or other water holding medium so it hold moisture, plus it needs to drain very well. If they sit in water, the tubers may rot. If you plant them in the garden, add copious organic material to your native soil, tilling in at least six inches (15 cm). Soil pH should be between 5.5 to 6.5, so if you use a lot of peat, you may need to add some horticultural lime to bring the pH up. Do not plant them in the ground before your soil temperature reaches 65ºF (18ºC).
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