A croton primer

Tuesday, January 26, 2010

Scorched leaves hanging
from twigs may mean
twig or branch dieback.

Jeff Searle, a nurseryman known for his exotic palms, has been growing crotons rather feverishly over the last five years, and he gave a whole course in growing them for the Tropical Fern and Exotic Plant Society this week.

Cold damage was the hot topic, of course. And he said leaves falling off are a better sign than leaves dying and hanging onto their twigs. Scorched and clinging leaves are not a guarantee that plants will die, but it doesn’t look good if that’s what’s happening. Cut back on watering and keep crotons on the dry side for now, he said.

Generally, crotons like semi-shade and not full sun, Searle told the society. They do best in acid soils. He uses the palm special fertilizer twice a year and sprays his plants with liquid azalea fertilizer once a month. (Azaleas also love acid.)

Yellow and green crotons usually grow larger and faster than the red-leafed varieties. They’ll also do better in full sun. Crotons with pastel leaves do well in shade. (Most crotons thrive in full morning sun or afternoon sun, but not midday sun, especially in summer.)

Mrs. Iceton is a pastel
croton that does best in

There are about nine different leaf shapes, Searle said, and they range from huge broad leaves 

Irene Kingsley is a croton with
oak leaf-shaped leaves.

(General Paget) to recurved leaves (Ramshorn). In between are oak leaf (Irene Kingsley) and semi-oak leaf (Sybil Griffin), spiral leaf (Dreadlocks), narrow leaf (Stoplight), very narrow leaf (Majesticum), small leaf (Aureo Maculatum) and interrupted leaf (Interruptum), which has a narrow piece of  midrib between most of the leaf and a rounded leaf tip. Because crotons are so genetically unstable, different leaf shapes and colors may occur on the same shrub. New to crotons are Thai hybrids, which are wonderfully curly-cued, but very slow-growing.

Croton scale is a new and aggressive problem for the plants. A natural enemy called the mealy bug destroyer does feed on it, but the scale may out-run the enemy. Horticultural oil is recommended for the crawler stage but requires several sprays; Bayer’s Advanced Tree and Shrub insect control can be used as a systemic drench.