Eggplant is a tropical perennial shrub, a relative of the tomato and the pepper, and, like them, one that gardeners here in North America grow as an annual. It is a warm-weather crop and demands a long, hot growing season to be truly productive. Yet grown on a spring-planted, summer-harvest schedule it will succeed just about anywhere in the continental United States, with the exception, perhaps, of coastal Washington and Oregon.
We put eggplants in the second part of our rotation, when the soil is mellow and well endowed, but not loaded with nitrogen. High levels of that essential nutrient lead all members of the nightshade family (Solanaceae) to produce luxuriant foliage but little fruit.
Like its relatives, most gardeners will need to sow seed indoors to guarantee the conditions young eggplant seedlings need. If there is one plant you would buy rather than start yourself from seed, however, this might be it, because the seedlings need both high temperatures and plenty of light to thrive, and there is a fairly wide range of types now available as transplants.
Start eggplant seedlings eight to ten weeks before the frost-free date. Germination temperature should be above the normal 72˚ F/122˚ C (our compromise level for the range of kitchen garden vegetables). Seedling growth is also much faster at higher temperatures. Each time the leaves of adjacent plants touch they should be transplanted to a larger container, finishing in a four- to six-inch pot.
Two weeks before transplanting prepare the bed by covering with black plastic to help raise soil temperatures; if you have drip irrigation tubing, lay it along the center of the bed first, and dump a shovelful of compost every 18-24 inches; that will guide you where to set the plants and give them an extra boost.
The plants should be hardened off gradually before being set out; they are more sensitive to transplant shock than just about any other garden vegetable. Come planting time, slit a hole in the plastic, gently set the plants just a tiny bit deeper than they were in the pot, and then turn on the water to settle them in their holes. We like to interplant basil and gem marigold plants along the edge in the bed, in alternation with the eggplants.
Once the plants are in, we cover them immediately with a floating row cover to moderate the normal June temperature swings and keep flea beetles at bay. The covers can generally be removed within about three weeks. From then on the plants won’t really require any attention beyond an occasional inspection for potato beetles, which consider eggplants their favorite food, even over potatoes. In fact, it is worth putting any extra eggplant seedlings you might have in the potato patch to attract them so they can be picked off and crushed.
The yellow-orange eggs of this beetle are laid in masses on the underside of leaves, and stretch in a cylindrical, bowling-pin fashion down from the leaf as they mature. Crush them before they hatch and you’ll save yourself a lot of trouble. Once the young grubs get going they can eat a lot of foliage before you even notice they’re there, and eggplants need all the leaf surface they’ve got if they’re going to ripen a decent crop.
In northern sections of the country, standard eggplants will bear four to six fruits per plant; warmer-climate gardeners can count on eight to ten, and in hot climates the plants may bear twelve to fifteen fruits. The smaller kinds bear proportionally more fruits, but the yield by weight is basically the same. There are an enormous number of varieties out there, though most are not easy to find. In 2002 we grew more than 80 kinds, and most ripened some fruit, even in northern Vermont!
Eggplants can be harvested anytime after they are about one-third their final size, which varies from the size of a marble to the size of a softball, depending on cultivar. I have found that, if conditions aren’t right, they will simply set fewer fruit, not smaller fruit. During a poor growing season we have had eight-inch-tall plants with a single twelve-inch-long fruit jutting unceremoniously from beneath its paltry leaves.