CORVALLIS - Eggplants are tropical in origin, therefore they are sensitive to cool temperatures. Members of the tomato family (Solanaceae), eggplants will not grow much or set fruit unless night temperatures are above 50 degrees.
In most parts of Oregon, eggplants should be planted as "starts," young plants with six to seven leaves. The best time to plant young eggplant starts out in the garden in Oregon is mid-May to mid-June, according to Jim Myers, Oregon State University professor of vegetable breeding.
To ensure vigorous plants that produce fruit earlier in the summer, protect eggplants with a cloche or water wall until June 1 or until the weather stays consistently over 50 degrees.
Depending on the variety and location of your garden, eggplants take about nine to 11 weeks of warmer weather to produce harvestable fruits. If you live in a coastal area or the mountains and plateaus of central and eastern Oregon, or in a cold pocket, you must help young eggplants along with a cloche, spun fiber row cover (example: Remay), or some other heat enhancing method.
Try making a cloche or hot cap by cutting out the bottom of a gallon plastic milk jug. Cover your plants until the first hot stretch of summer.
Home gardeners all over the state can also help eggplants reach maturity sooner by warming the soil at planting time. Try mulching eggplant starts with black plastic or by covering them with spun fabric row cover. Plant eggplants about two feet from each other in fertile soil. Four to six plants should produce enough eggplants for a family of four.
A common mistake is to harvest eggplants too late. Eggplant should be harvested after they reach the proper size and color for their type, but before their fruit becomes seedy and bitter.
"The luster of the skin is a good indicator of readiness for harvest," said Myers. "If they are glossy, the fruit should be good. If the skin looks dull, then it is over the hill. If left on the plant too long, they will become tough and off flavored."
With white and light-colored varieties of eggplants, don't wait until the fruits turn yellowish, as this indicates they are over mature. In purple or black fruited types, this over maturity is difficult to see.
There are several types of eggplants including the classic large pear-shaped black-colored varieties, the elongated pear small fruited types and the small to medium round black fruited types. There are many new different colored varieties and shapes on the market as well.
Verticillium wilt is the main disease in eggplants in Oregon, according to Myers.
"There's not much we can do about it, though," said Myers. "It causes leaf browning and necrosis (tissue death) that is evident at the end of the growing season. All varieties are susceptible, some more than others."
The OSU Extension Service recommends the following varieties of eggplants as growing well in most areas of Oregon, except at the coast or the higher elevations of the state, where a protective cloche is needed: Dusky, Epic, Bambino (round), Cloud Nine, Black Bell, Calliope, Burpee Hybrid, Millionaire, (elongated) Megal, Bride, Orient Express. All of these varieties have shown tolerance to verticillium, said Myers.