By Russell T. Nagata
By Russell T. Nagata
University of Hawaii at Manoa
College of Tropical Agriculture and Human Resources
Komohana Research and Extension Center
As we celebrate Easter today, it is only fitting to write about the eggplant, Solanum melongena. The eggplant is an easy-to-grow garden vegetable, or fruit if you like, and can be very versatile in the kitchen. It is of ancient origin, probably domesticated somewhere in Pakistan, India, Bangladesh and Burma some 4,000 years ago.
From this, it slowly spread around the world, first as an ornamental garden plant and later as a food crop. Eggplant is the English name and was used to describe an early English variety that resembles an egg: oval in shape and white in color. Throughout most of Europe, the eggplant is known as aubergine. The eggplant belongs to the nightshade family, Solanaceae, which also includes tomato, white potato, tobacco and peppers.
President Thomas Jefferson is credited with introducing the eggplant to the continental United States at around the same time that it was introduced into Hawaii by Don Francisco de Paula Marin. De Paula Marin brought eggplant to the islands around 1800 along with many of the garden vegetables and fruits we grow today, such as apples, asparagus, avocados, cabbage, carrots, chili pepper, lemons, limes, macadamia, olives, onion, oranges, parsley, peas, peaches, pears, potatoes, rice, tea and tobacco.
When growing eggplant, the best advice to newbies is to plant in well-drained soil. If the spot you selected puddles when it rains or remains soggy for days after it rains, you will have trouble growing eggplant in your garden. While eggplant can be direct-seeded into your garden, it is best to use 5- to 7-inch-tall transplants, since they grow slowly during the seedling stage, usually taking five to seven weeks from seed to transplant size.
Eggplant is a heavy feeder when growing vigorously, and to maximize fruit production, plan accordingly. A soil test can properly determine pH and the amount of fertilizer required for your garden soil. Soil pH should be between 5.5 and 6.8.
Alternatively, if you don’t have a soil test, you can do the following: for infertile soil, use 1 to 1.5 pounds of fertilizer such as 10-30-10, or add 10 to 20 pounds of well-aged compost or manure to 100 square feet of garden prior to planting. At fruit set, apply 1 to 1.5 pounds of 10-30-10 or 10-20-20 fertilizer per 100 square feet of garden. Place the fertilizer in a 6- to 8-inch band around each plant. One to two tablespoons of nitrogen fertilizer such as sulphate of ammonia can be sidedressed 8 to 12 inches from the eggplant stem every two weeks to improve fruit size.
Many insects, mites and nematodes can cause poor plant vigor and loss of fruit yield. Plant hoppers, aphids, stinkbugs and whiteflies can suck the life out of leaves, stems and fruits as well as spread viruses and other diseases. Thrips are attracted to the flowers, where they can damage the stigma and pollen grains, thereby preventing pollination and fruit set. Feeding on the young, developing fruit can cause fruit deformity and zipper-like tracks on the skin.
Some varieties of eggplant are resistant and fairly tolerant of the rootknot nematode, but heavy infestation can cause plant stress, making the plant more susceptible to drought, water-logged soils and infection by diseases.
In Hawaii, diseases on eggplant can be very common, especially when grown under rainy, humid conditions on the windward side of the island. Bacterial wilt is caused by a soil-infesting bacteria that can persist for many years in the garden soil, causing sudden wilting of the entire plant without prior indications of disease infection. In many cases, plant yellowing will not be observed prior to plant death.
Other diseases, such as pythium and rhizoctonia, are common organisms that can cause damping-off of young seedlings. Still, other organisms cause leaf and fruit necrosis, wilts and stem girdling on mature plants.
While different fruit characteristics are favored in different parts of the world, in Hawaii choices abound due to our cosmopolitan population and great growing conditions. In general Europe and the continental United States, gardeners like to grow the large globes with dark purple skins such as Black Beauty. Italian types are smaller-globed. The long, skinny types are noted as Japanese, while the Chinese types are not as skinny as the Japanese types, and the Thai cherish a small, green ping-pong ball sized eggplant.
Some varieties have a stronger, more bitter taste than other varieties, and can be influenced by fruit age and growing conditions. Eggplant is naturally low in calories, with only 28 calories per cup of boiled fruit. It is also a good source of calcium, magnesium, potassium and phosphorous, and the skin of the eggplant is high in soluble fiber.
For more information on this and other gardening topics, please visit the CTAHR electronic publication website at http://www.ctahr.hawaii.edu/Site/Info.aspx, or visit any of the local Cooperative Extension Service offices around the island. I can be reached at russelln@hawaii.edu.