Weeding around the young transplants is essential. "Weeds will outcompete eggplants until warm summer temperatures come," says Kole Tonnemaker, who grows eggplant at Tonnemaker Hill Farm in Washington State. So stay on top of weeds by regularly hand-pulling or carefully weeding with a hoe or cultivator. Once the soil is warmed up, a mulch of straw or compost can be used. Grass clippings, too, make a good antiweed barrier, but make sure the clippings are from untreated lawns.
Aphids tend to cluster on the undersides of the eggplants' foliage but are easily controlled with insecticidal soap. Flea beetles—skittish, tiny black or brown insects—chew small, shotlike holes in the leaves of eggplants. Larger plants tolerate this damage, but the beetles usually strike in early summer, when the plants are still small and vulnerable. Planting arugula or mustard greens nearby can lure flea beetles away from eggplants, as the pest prefers to feed on the greens. Colorado potato beetles can cause significant damage, chewing large holes into the soft green, somewhat fuzzy foliage. "We remove them by hand," says Tonnemaker. "When adults are present, we check the undersides of leaves for egg masses and squish them. A thorough job on the first generation (late May to June here) has given us season-long control." Neem-oil spray is a good multipurpose defense if applied routinely.
Placing a floating row cover over seedlings right after planting offers a twofold benefit: It forms a physical barrier between the plants and insect pests, and the row cover acts as a greenhouse, heating the air around the plants above the ambient temperature. This lightweight, nonwoven material can be draped directly onto the plants or tented over the row, supported by wire hoops. Eggplants are self-fertile, so the cover may be left on all season if necessary, but the plants will produce more fruit if it's removed to let pollinating insects cross-pollinate the flowers.
Eggplants are susceptible to a number of plant viruses and fungal diseases. If these are a recurrent problem, try one of the resistant varieties: 'Dusky' resists mosaic virus, and 'Nadia' resists verticillium wilt. Once the plants flower and begin to set fruit, take care to keep the soil moist, watering from the base in cool moist zones, which will also help to prevent fungal disease. Use a drip-irrigation system or soaker hose.
Eggplant fruits typically form from the bottom of the plant up and can be harvested at any time. The fruit is best, however, when the skin is glossy and the flesh still tender, before the seeds begin to harden. To determine if it is time to harvest, press the fruit with your thumb: If no indentation occurs, the fruit is not ready; if the indentation remains, the fruit is overripe; if it rebounds, it is time to harvest. Clip the eggplants off the plant with pruning shears, keeping the cap and about 1 inch of stem intact. Watch out for the small prickles that line the stems and the cap of some varieties, as they are a skin irritant.
Temperatures below 50°F cause the seeds and flesh of eggplants to brown and the skins to take on a bronzy cast. To refrigerate, individually wrap the eggplants in plastic film and store in the warmest part of the fridge for no more than 2 days. An eggplant is at its very best when used just after picking, however, so make that the goal. It is an excellent source of dietary fiber and has valuable minerals and antioxident compounds, and can even help to reduce cholestrol when part of a controlled program of diet and exercise.