Introduced to North America by Thomas Jefferson, the aubergine (Solanum melongena) became known as eggplant because of the resemblance of a popular cultivar to a goose's egg. The aubergine originated in Asia, and the cultivar common in Japan -- called nasu in Japanese -- is the one known in the rest of the world as Japanese eggplant. Its fruit -- which is technically classified as a berry -- is smaller and more slender than North American varieties, and it has a distinctive, delicate taste. Japanese eggplant is hardy is United States Department of Agriculture zones 4 through 10, and it grows well in containers.
Planting Japanese Eggplant
Japanese eggplant is a warn-season crop and thrives in full sun, well-drained soil and the soil should be slightly acidic, with a pH between 6.2 and 6.8. Dig up the soil before planting and turn it with with a rich compost and an application of 5-10-10 fertilizer applied at the rate of 3 pounds per 100 square feet. Water the fertilizer into the soil after applying. Space the holes 24 to 36 inches apart to accommodate the large, bushy plants.
Japanese eggplant does best in warm soil, so if you live in a cooler climate, cover the holes with black plastic for a few days prior to planting or consider growing them in large black plastic containers, which retain heat better than open soil. In colder climates. it's also a good idea to protect the young plants with row covers you can open during the day. This also provides protection from pests, primarily flea beetles. Wait until any unexpected frosts or freezes leave your region before growing heat-loving eggplants as they will not perform well in cool weather.
Prepare for Bounty
Japanese eggplant is a prolific producer, and it's common for mature plants to fall over when they are full of fruit. It's wise to prepare for this by staking the young plants when you plant them, even though they won't really need the stakes until they grow to a height of 24 inches. Installing the stakes at the time of planting ensures the root system isn't damaged. Tomato cages also work well in supporting the eggplants. To create bushier growth and more fruit, pinch the juvenile growth tips any time after the plants reach 6 inches high.
Watering and Fertilizing
The soil should not be allowed to dry out during the growing season, especially during fruiting or the plant may wilt and the fruit will be small and bitter. Supply 2 inches of water per week; it's best to to keep the soil moist to a depth of 6 inches. Plants grown in containers may require daily watering as the soil dries quicker. If the top inch of soil is dry, water the plant. Fertilize twice during the growing season -- once when the fruits are the size of quarters and once three weeks later -- using 1 1/2 ounces of calcium nitrate for every 5 feet of garden bed. Water the fertilizer into the soil after applying.
Harvesting the Fruit
It's important to avoid allowing the fruit to overmature on the plant -- it tastes bitter, and the practice discourages the plant from producing more fruit. Harvest can occur 16 to 24 weeks after planting. Pick the fruit when the skin is a shiny purple and it bounces back when you press it with your thumb; the fruit is underripe if you can't push in the skin and overripe if the depression remains after you remove your thumb. Cut close to the fruit, leaving about an inch of stem attached. Japanese eggplants can be harvest when they are the size of a finger to the size of a hotdog, depending on the cultivar.