From the Help Desk of the Master Gardeners of Contra Costa County

Client– Thank you for stopping by the Master Gardeners table at the recent Lafayette Harvest Festival with your request for information on increasing your eggplant yield. 

MGCC Help Desk Response:  One key factor for growing more eggplants is temperature. Eggplants like warm temperatures:  a daytime temperature between 75 and 85 degrees ^oF and a nighttime temperature at or above 65 degrees ^oF. Those temperatures are key to blooming, pollination, and fruit growth. Colder temperatures can stop plant and root growth, reducing plant vigor and yields.

To avoid the cold, make sure that you hold off setting out plants for at least a month after the last frost date. For Lafayette, the recommendation would be to wait until after April 15^th to plant; just after May 1^st is even better. If possible, select a warm, sheltered spot in your yard. However, this can be somewhat complicated by the guidance that you should not plant eggplants (or members of the Solanaceae family… tomatoes, potatoes, etc.) in the same place but once every three years to prevent the buildup of soil pests. A warm spot is particularly important in Lafayette since it typically has cool nights. Early in the season, you may want to use hot caps or row covers to increase the temperature. Note that any protection that covers the plants must be removed when the plants begin to flower.

For greater yield, make sure that your eggplants have a lot of space in the garden. Plants should be spaced in rows three feet apart, allowing two feet between plants. Eggplants have deep roots. Make sure the soil is loose and well pulverized. Digging deep helps make essential nutrients more available and helps plants grow deeper roots. Information on preparing the soil and adding amendments is available in this University of California document on vegetable gardening (see page 2):  http://anrcatalog.ucanr.edu/pdf/8059.pdf.

Make sure that you keep the bed weed free. Mulching will help cut down on the weeds and preserve moisture, although you may not want to mulch too deeply since mulch can keep the soil cool.

Eggplants are moderate users of nitrogen and phosphorus. Fertilizer or manure should be thoroughly mixed into the top six inches of soil before you plant.  Recommended fertilizer levels are 10 pounds of dry manure (make sure it is well composted) or 1/3 pound of commercial 12-12-12 fertilizer per 10 square feet of garden. After flowering begins, make additional light nitrogen applications as fruit grows. Maintain moderate nitrogen levels until harvest. Too much nitrogen will lead to excessive vegetative growth at the expense of eggplant production.

eggplant growing in pot
pix: ourhappyacres.com

Even watering is needed. Drip irrigation works well. Water is particularly important during bloom, fruit set and fruit enlargement. Plants lacking water will be stunted and develop fruit that is pithy. Mature plants have roots to 3 feet deep so wet soil deeply during the fruiting period.

Plants will need warm nights and long hot days to ripen the slowly developing fruit. For the standard varieties that yield large, plump fruits, thin the fruits so that there is only one per the main branch, or three to six per plant. It is not necessary to thin the smaller varieties or the Oriental types.

Plants will stop fruiting as fall cool temperatures take effect.

For overviews on growing eggplants, please see:
http://ucanr.edu/sites/ucmgnapa/files/153890.pdf
http://vric.ucdavis.edu/pdf/eggplant.pdf

For more detailed information on eggplants, see http://www.ipm.ucdavis.edu/PMG/GARDEN/VEGES/eggplant.html. 

Good luck with your garden. Please let us know if you have further questions.

Master Gardeners of Contra Costa County (ECS)

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Note: The  UC Master Gardeners of Contra Costa's Help Desk is available year-round to answer your gardening questions.  Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA  94523. We can also be reached via telephone:  (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog.