Summer Squash

Sowing: Direct-sow seed after the danger of frost has passed and the soil has warmed, or get a head start by sowing indoors in 3-inch containers about three weeks before planting out, handling the transplants gently since the roots resent disturbance. Thin seedlings by snipping rather than pulling, leave the strongest single plant, give the crop full sun of 6 to 10 hours a day, and sow a second planting in early-to-mid July to keep fruit coming. Space plants in hills of two to three, 3-4 feet apart with 4-6 feet between rows, or as single plants 2-3 feet apart with 3-5 feet between rows.

Feeding and watering: Summer squash has a medium nutrient requirement, so work compost or fertilizer into the soil before planting and side-dress once female flowers begin to appear. Water deeply at the base of each plant, especially in hot, dry weather and once the first fruits start to form, and mulch around the plants to conserve moisture and suppress weeds.

Growth habit and pollination: The plant grows as a bush rather than a true vine, though its stems can sprawl and root where they touch the soil, which increases fruit production and helps the plant tolerate vine borer damage to the main stem. Because it is monoecious, male flowers open first and female flowers follow one to two weeks later; fruit set depends on bees carrying pollen between them, so pesticide use should be avoided during bloom and cool, rainy weather can reduce pollination.

Pests reported on summer squash include cucumber beetles, squash bugs, squash vine borers, aphids, leafminers, cutworms, mole crickets, fruit worms, spider mites and slugs. Diseases include bacterial wilt, Choanephora fruit rot, scab, Phytophthora blight, downy mildew, powdery mildew, mosaic virus and other fruit rots, with mildews and viruses causing the greatest losses in summer and fall plantings; the natural light greenish-gray mottling on zucchini leaves is often mistaken for mildew and should be checked closely before treating.

Poor pollination shows up as wrinkled, misshapen fruit or premature fruit drop, a problem that is more common during rainy spells when bees are less active.

Picking: Harvest fruit while still immature and the rind is tender, checking plants daily once they begin to bear. Elongated types are cut at about 6 to 8 inches long, pattypan types at 3 to 4 inches across, and crookneck types at 4 to 7 inches long; cut the stem so an inch or two remains attached to the fruit, wearing gloves since the stems can carry irritating spines. If the rind can no longer be marked with a thumbnail the fruit is over-mature and should be removed to let new fruit develop.

Storage: Because summer squash keeps far less long than winter squash, fruit should be used within 5 to 14 days when held in cool, moist conditions around 32-50°F and 90% relative humidity.

Culinary: The tender flesh, skin and seeds are all edible, cooked or raw, and the squash is often sliced thin lengthwise as a noodle substitute. The bright yellow male flowers are also harvested for culinary use, sought after by restaurants when picked with intact stamens just before or as they open, and the fruit is valued as a source of folate, potassium, and vitamins C and B6, with unpeeled squash also contributing vitamin A. Summer squash is additionally used in value-added products such as breads and relishes.

Summer squash belongs to Cucurbita pepo, a New World species native to North America that has been cultivated across the Americas for at least 7,000 years. Extensive interbreeding among cucurbit forms over that long history produced the wide range of shapes and colors seen in squash today, and after European contact in the 16th century these cucurbits spread from the Americas to be grown worldwide.