Damrosch reports that her farm recently experimented with grafting her favorite eggplant varieties onto an extravigorous rootstock, a technique that combines two different plants: The top of the plant is a variety selected for its high-quality fruit, and the rootstock, or bottom, of the plant is a variety known for its disease resistance and vigor. The result yields a superhealthy,
fast-growing eggplant. "Grafting works great," says Damrosch, "but it's a tricky procedure that only a very adventurous home gardener would want to try." Fortunately, grafted eggplants are now available from some specialty nurseries, including Territorial Seed Company, which plans to ship grafted eggplant seedlings in spring 2012.
Eggplants grow into bushy plants 2 to 3 1⁄2 feet tall. The larger a plant grows, the more fruit it supports. The key to achieving a generous late-summer harvest is to encourage strong, healthy growth as soon as the plants are in the ground. Begin prior to planting by working 2 to 3 inches of compost into the soil, adding a balanced granulated organic fertilizer at the same time (follow the manufacturer's recommended application rates). Plant out seedlings when the soil is 65°F or warmer and all danger of frost has passed.
In climates with long, chilly springs or short summers, black plastic mulch helps eggplants thrive, though it's not the most aesthetically pleasing option. Ground covered by black plastic will be 8°F to 10°F warmer than uncovered soil. Plastic films also help to inhibit weed growth. Recommended brands are Solar Mulch, which is a dark plastic material, and biodegradable black cornstarch-based films such as BioTelo. To use these mulches, stretch the material smoothly across the bed and then pin it into place with landscape-fabric staples. Punch planting holes with a bulb planter or cut Xs through the material at each planting spot.
Transplants should be set no deeper than they were in their pots, and spaced at least 18 to 24 inches apart in rows 2 feet apart. When the first set of flowers emerge, pinch them off, recommends Rosalind Creasy, author of Edible Landscaping (Sierra Club, 2010). In addition to making the plant develop several fruiting branches, this will, she says, "encourage the plant to put more energy into creating leaves and roots instead of one big fruit." Creasy fertilizes her plants with homemade compost and a little chicken manure when planting, and applies fish emulsion about 6 weeks later. To keep plants upright and fruit clean and intact, she recommends staking with bamboo poles.
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.
Sow Your Own
Starting eggplants from seed sown indoors opens the door to an amazing range of varieties that are typically not available as transplants at nurseries.
Opt for fun varieties. Baker Creek Heirloom Seeds lists more than 60 eggplant varieties, including "Listada de Gandia', an Italian heirloom that gardening writer Rosalind Creasy names as one of her favorites. Kitazawa Seed offers a range of Asian varieties, such as 'Konasu', a marble-sized Japanese eggplant with deep purple skin.
Start early. Sow seed about 9 weeks prior to planting-out date—for instance, to plant out in the first week of June, sow seeds the last week of March. Eggplant seeds germinate best in soil that is above 75°F, so place the seed trays on an electric heat mat.
Give them room. Eggplant seedlings grow fairly slowly. When the seedlings reach 2 or 3 inches tall, transplant into 4-inch pots to allow room for strong root systems to develop.
Harden off thoroughly. Before transplanting, transition the seedlings to the garden by gradually lengthening the time they are exposed to outdoor conditions. A 10-day hardening-off period is usually adequate.
Pretty in Pots
Eggplants grow well in containers. The technique is especially helpful in cool climates, because you can move the pot to a sunny, warm, sheltered spot. Rosalind Creasy gives the following advice:
Keep it clean. "I've had great success preventing disease by planting eggplants in containers filled with sterile potting mix," says Creasy. Empty and clean the pots annually before adding fresh potting mix.
Ornament the edibles. Plant the eggplant in the center of the container and surround it with colorful annual flowers, such as purple and pink petunias that will trail over the sides, suggests Creasy.
Go big. "When eggplants are grown in containers that are at least a foot-and-a-half off the ground, the flea beetles don't seem to find them as easily," notes Creasy.