How to grow warm-season vegetables successfully - includes article on how and when to harvest crops - Special Issue: Spring-Summer 1994 Garden Guide - Planting & Maintenance Guide

Sunset, Spring-Summer, 1994

Timing is the key to success when you plant warm-season crops like corn, peppers, and tomatoes. Many, such as peppers, need warm soil from the beginning; without it, seeds won't germinate, and plants will grow slowly--if at all. In cold-winter climates, plant too early and the lightest frost can kill these crops; plant too late and they may not mature before the short growing season ends. In hot-summer areas (low and intermediate deserts), plant too late--after daytime temperatures have begun to rise into the 90s and nighttime temperatures stay above the high 70s--and pepper and tomato blossoms usually drop off the plant, preventing fruit set; high temperatures can also shrivel corn pollen so ears aren't pollinated.

But no matter where in the West you live, the time to plant warm-season crops is mid- to late spring. The charts on pages 72 through 75 show approximate planting dates for popular warm-season crops in the West's major climate zones. Find your zone in the listing below the charts, then look at the charts to find the planting dates for the various crops.

Earliest planting times for specific vegetables are based on average dates of last spring frosts and predicted soil temperatures (soil needs to be warm enough for seeds to germinate). Use them as guidelines only. Even though Sunset climate zones are quite specific, the microclimate of your garden may be different because of orientation to the sun, soil type, and trees and surrounding structures. Also, weather varies from year to year. If you're unsure about frost dates in your area in spring and fall, call your cooperative extension office or a nearby nursery.

Keep in mind that the varieties you grow also contribute to your success with warm-season crops; some varieties, for example, are bred for short-season climates.

Planting seed versus transplants

The charts recommend planting either by directly seeding outdoors (S) or using transplants (T). Starting vegetables from seed offers a wider selection.

Most warm-season crops can be started from seed indoors, then transplanted as seedlings into garden beds. Corn is one exception. Sow it directly in the ground. You can start melons indoors, but be careful not to damage the delicate root system when transplanting melon seedlings.

To grow transplants, sow seed in flats or sixpacks filled with sterile potting soil. Place in a warm, well-lit location and keep moist. If needed, move seedlings to larger pots when they develop their first true leaves. Fertilize all crops weekly with dilute liquid fertilizer until transplant time.

Finally, don't be fooled by the weather. A spring heat wave can damage young plants as much as a cloudburst, but weather doesn't affect planting dates much. (Remember, it's the soil temperature that really matters.) Use season extenders such as row covers, raised beds, cloches, or mulches to modify weather effects and protect plants.

The warm-season vegetables listed in the charts on the following four pages can be planted in spring. To learn approximate planting dates for your area, find your climate zone in the lists below the charts, then look up the crops on your climate zone's chart.

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Zone 1: Coldest winters in the West. Here (Bend and Billings are good examples), latitude and elevation contribute to biting, snowy winters. Frosts can occur any day of the year; a typical growing season lasts not much longer than 100 days, but can go up to 180 days in some parts.

Zone 2 and 3: Milder, snowy winters. In zone 2 (Denver, Salt Lake City, Spokane, Yakima), growing season averages 150 days. In more moderate zone 3, it averages 160 days; in Walla Walla, about 220 days.

Zone 4: Cold-winter parts of Western Washington. West of the Cascades (Bellingham, Olympia, Puyallup), this zone has a greater frequency of low temperatures than zone 5; it also has more rainfall and a shorter growing season (average 200 days).

Zone 5: Marine influence along the Northwest coast and Puget Sound. Mild ocean air and relatively warm winters characterize this area (Everett, Seattle, Tacoma). Growing season may run to 250 days in some parts, but many waterside areas don't accumulate much heat in summer (the reason lima beans, eggplant, and watermelon don't thrive at all). For other crops, choose hottest spots to grow such heat lovers as peppers.

Zone 6: Willamette Valley. This zone is warmer than zone 5, and the growing season lasts about 200 days.

Zone 7: Oregon's Rogue River Valley. In this area of hot summers and mild but pronounced winters, growing season lasts about 175 days.

TABULAR DATA OMITTED

Zone 7: The foothills. Here, elevation and microclimates dictate planting times. Areas quite close to one another could have very different dates for last frost. For example, near Auburn, last frost usually occurs in mid-March. But near Nevada City, less than 30 miles north, frost doesn't usually end until the second week of May; gardeners there have to wait several more weeks to plant. Even with these fluctuations, most regions have enough summer warmth for bumper crops.