Growing guidelines: Mulch immediately after transplanting, and gently hand pull any invading weeds. Interplant an early crop, such as lettuce, between the eggplant transplants. When the eggplants bloom, apply more liquid fertilizer and repeat monthly. For best production, plants need 1 to 1½ inches of water a week.
Problems: Flea beetles, which chew many tiny holes in leaves, are eggplant's worst pest. To avoid this problem, keep plants indoors until early summer, or cover outdoor plants with floating row cover or dust the foliage with kaolin clay (reapply it after rain). If plants become infested, spraying Beauveria bassiana or spinosad may knock back the population of flea beetles and save your plants.
Hand pick and destroy yellow-and-black-striped Colorado potato beetles and the yellow masses of eggs they lay on leaf undersides. Hand picking is also effective for tomato hornworms, 4-inch green caterpillars with white stripes. Don't destroy those covered with tiny white cocoons; these contain the parasitic offspring of the beneficial braconid wasp. Tiny spider mites cause yellow-stippled leaves; control these pests by knocking them off the plant with a spray of water.
The most common eggplant disease is Verticillium wilt. Avoid it by planting resistant cultivars and by rotating crops.
Harvesting: Pick eggplant when the skin takes on a high gloss. To test, press the skin. If the indentation doesn't spring back, that fruit is ready for harvest. To harvest, cut the stem with a knife or pruning shears. Eggplants will keep for 2 weeks if refrigerated. If you cut open an eggplant fruit and find that the seeds inside have turned brown, the fruit is past prime quality and the flavor may be bitter. The best way to avoid this is by picking fruits on the young side, when they are 1/3 to 2/3 of their fully mature size.