How to Grow Summer Squash

Squash zucchini on slatSummer squashes are frost-tender, warm-season annuals. The most popular are crookneck, straightneck, scallop, and zucchini. Sow squash seeds in the garden–or set out seedlings started indoors–only after the soil has warmed to at least 60°F, usually no sooner than 3 weeks after the last frost in spring. Summer squashes grow best in air temperatures ranging from 60° to 75°F; established fruit will ripen in temperatures as high as 100°F but flowers will drop in high temperatures.

Description. Squashes are a large group within the cucumber family, Cucurbita, and include gourds, pumpkins, and summer and winter squashes. Summer squashes are eaten when they are immature, usually when their skins are soft and thin; winter squashes are eaten mature after their skins have thickened and hardened. Summer squash commonly grows as a bush or smaller weak-stemmed vining plant. Squashes have large, broad leaves; 4 to 6 stems or short vines grow from a central root. Fruits vary in shape from round to cylindrical to scalloped much as their names imply: crookneck, straightneck, scallop, and zucchini. Separate male and female flowers appear on the same plant.

Yield. Grow 1 or 2 summer squash plants per household member.

Site. Plant squash in full sun. Grow squash in loose, well-drained soil rich in organic matter. Prepare planting beds in advance working in plenty of aged compost. Add aged manure to planting beds the autumn before growing squash. Squash prefers a soil pH of 5.5 to 6.8. Summer squashes will sprawl slightly; if space is tight train them over small A-frame trellises.

Planting time. Summer squashes are frost-tender, warm-season annuals. Sow squash seeds in the garden–or set out seedlings started indoors–only after the soil has warmed to at least 60°F, usually no sooner than 3 weeks after the last frost in spring. Start squashes indoors as early as 4 weeks before the last average frost date in spring. Sow seed indoors in biodegradable peat or paper pots that can be set directly in the garden so as not to disturb plant roots. Summer squashes grow best in air temperatures ranging from 60° to 75°F; established fruit will ripen in temperatures as high as 100°F but flowers will drop in high temperatures. Squashes are warm-season crops and very sensitive to cold and frost. Summer squashes require 50 to 65 days to reach harvest.

Planting and spacing. Sow squash seeds 2 to 3 inches deep. Sow squash in raised hills or inverted hills 4 to 5 seeds set 3 to 4 inches apart; thin to the two strongest seedlings. Space hills 6 to 8 feet apart. In rows, plant 2 squash seed 10 inches apart in rows 3 to 5 feet apart; thin successful seedlings in rows to 3 feet apart. Thin seedlings by cutting off weak seedlings at soil level with scissors so as not to disturb fragile roots. Hills or mounds should be 6 to 12 inches tall and 20 inches across. This will allow plants to run down the hill away. Inverted hills–which can be used to retain moisture in dry regions–can be made by removing an inch of soil from an area about 20 inches across and using the soil to form a ring or circle. Plant 4 or 5 seeds in each inverted hill. Summer squashes can be trained up a fence or trellis. Set supports in place at the time of planting so as not to disturb growing roots.

Water and feeding. Squash grow best in soil that is kept evenly moist. Squashes require a lot of water in hot weather. Plants may wilt on hot days as they use water faster than the roots can supply. As long as water is regular and deeply applied, wilted plants will liven up as the day gets cooler. Squash that is wilted in the morning needs immediate water. Add aged compost to planting beds before planting and side dress squash with aged compost at midseason. Side dress squash with compost tea every 2 to 3 weeks during the growing season. Avoid feeding squash with a high nitrogen fertilizer, 5-10-10 is best.

Companion plants. Nasturtiums, bush peas, beans. Avoid planting summer squashes in the shadows of taller plants.

Care. Squash have separate male and female flowers. The first flowers to appear are male flowers which will not produce fruit. Female flowers appear slightly later and are pollinated by the male flowers commonly with the help of insects. If pollination is slow or does not occur, use a soft-bristled brush to dust inside a male flower then carefully dust the inside of a female flower (a female flower will have an immature fruit on its stem, a male won’t).

Once fruits form set each one on a wooden plank so that it does not have direct contact with the soil; this will allow squashes to mature with less exposure to insects.

Container growing. Bush-type summer squash can be grown in containers. Sow 2 or 3 seeds in the center of a 10-inch container; thin to the strongest seedlings once plants are 3 to 4 inches tall. Extend the growing season by planting early and moving pots indoors when frost threatens. Set a cage or trellis in place at planting to save space.

Pests. Squash can be attacked by squash bugs, squash borers, and cucumber beetles. Hand pick or hose away beetles. A small hole in the stem or unexplained wilting may indicate the presence of borers. Slit the stem, remove the borers, and dispose of them. Cover the slit stem with soil to encourage root development from that point.

Squash borers or bacterial wilt can cause squash plants to suddenly wilt and die just as they begin to produce. Bacterial wilt can be spread to squash by cucumber beetles; handpick and destroy cucumber beetles.

Diseases. Squashes are susceptible to bacterial wilt, mosaic virus, and mildew. Plant disease-resistant varieties. Keep the garden clean and free of debris where diseases and pests may harbor. Water at the base of plants to keep water off the foliage, and do not handle plants when they are wet to avoid the spread of fungal spores. Remove and destroy infected plants before they spread disease to healthy plants.

Powdery mildew, a fungus disease, will cause leaves to turn a gray-white color late in the season. Proper spacing and increased air circulation will help reduce this problem.

Mosaic virus can cause squash plants to become mottled yellow and stunted. Mosaic virus is spread by aphids. Control aphids and remove affected plants.

Blossom end rot will cause squash fruit to rot from the blossom end. Blossom end rot is caused by fluctuations in soil moisture. Water evenly and regularly and mulch around plants to conserve soil moisture.

Harvest. Summer squashes are ready for harvest 50 to 65 days from sowing. Pick summer squashes young when rinds are still tender and before seeds have formed. Harvest zucchini and crookneck varieties when they are 5 to 10 inches long (4 to 7 inches long for yellow varieties); harvest scallop and round types when they are 3 to 5 inches in diameter. Break the squashes from the stem, or use a clean knife to cut the fruit away. Do not let summer squash mature; that will suppress flowering and reduce the yield.

Squash flowers are edible. Pick and eat male flowers so as not to reduce the productivity of the plants. Squash flowers are often dipped in a batter and deep-fried.

Varieties of summer squash:

Crookneck: Aztec (55 days); Bandit; Crescent (53 days); Early Summer Yellow (53 days); Golden Dawn; Horn of Plenty; Medallion; Milano (42 days); Sundance (52 days); Supersett (50 days).

Straightneck: Butterstick (50 days); Early Prolific (50 days); Enterprise; Gold Slice; Goldbar (50 days); Multipik; Precious; Seneca Prolific (51 days); Sunbar (43-54 days).

Scallop or pattypan: Benning’s Green Tint (54-63 days); Butter Scallop (50 days); Golden Bush (68 days); Patty Pan (50 days); Peter Pan (60 days); Scallopini (60 days); Sunburst (50 days); Yellow Custard (50 days).

Zucchini: Ambassador (55 days); Aristocrat (48 days); Arlesa (45 days); Black Beauty (58 days); Black Jack (55 days); Chefini (51 days); Clarimore Lebanese (44 days); Cocozelle (striped-45 days); Condor (48 days); Costata Romanesco (80 days); Dark Green (44-60 days); Elite; Embassy (49 days); Gold Rush (50 days); Golden Dawn (45 days); Goldfinger (41 days); Greyzini (55 days); Jackpot; Lebanese Light Green (40 to 50 days); Magda (45 days); Midnight; Milano (42 days); Onyx; Raven (42 days); Ronde de Nice (45 days); Round Green (52 days); Seasons; Seneca (47 days); Spacemiser; Spineless Beauty; Tatume (52 days) ; Tipo (55 days); Viceroy.

Storing and preserving. Summer squashes will keep in the refrigerator for up to one week. Do not wash squashes until you are ready to use them. Cooked squash can be frozen, canned, pickled or dried.

Common name. Summer squash, crookneck, pattypan, straightneck, scallop, zucchini.

Botanical name. Cucurbita species.

Origin. American tropics

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