How to Grow Summer Squash From Seed

Summer squash is a warm-season crop that will not tolerate any frost, so timing is simple: wait until all danger of frost has passed and the soil has warmed to at least 65 to 70F. In most gardens that means late spring, a week or two after your average last frost. Because plants grow and produce so fast, direct sowing outdoors is the norm. For a steady supply, sow a second round three to four weeks after the first, and in long, hot-summer regions you can plant again in midsummer for a fall crop.

Summer squash is almost always direct-sown right where it will grow. Build a low hill or mound of loosened, compost-rich soil, and sow four or five seeds about an inch deep near the center of each hill. Space hills 24 to 36 inches apart to give the big leaves room and air. Keep the soil evenly moist until seedlings emerge in about a week, then thin to the two or three strongest plants per hill. Mixing a little compost or a pinch of mycorrhizal fungi into each hill at sowing gives the fast-growing roots a strong start.

Summer squash is hungry and thirsty. Give it full sun, rich soil, and about an inch of water a week, always at the base rather than over the leaves to keep powdery mildew at bay. Mulch to hold moisture and feed with a balanced fertilizer at planting and again once fruit starts forming. Watch closely for squash bugs, squash vine borers, and cucumber beetles: check leaf undersides and stem bases often, crush the bronze egg clusters you find, and float a row cover over young plants (lifting it once flowers open so bees can reach them). The plants need pollinators to set fruit, so if bees are scarce you can hand-pollinate.

Summer squash grows well next to plants that pull in pollinators and confuse its pests. Marigolds, nasturtiums, and aromatic herbs like basil are classic partners, while corn and beans make a traditional trio in larger beds. These three are especially easy to add in one click:

Pick summer squash young, tender, and often. Zucchini and marrow types are best at 4 to 6 inches, patty-pans when they are palm-sized, and crooknecks while the skin is still soft enough to nick with a fingernail. Cut the fruit off with a knife or shears rather than twisting, leaving a short stem. Harvest every one to two days at peak season, because frequent picking keeps the plant flowering and producing right up until frost, while a few overgrown fruit will slow it to a stop.

Summer squash is one of the most versatile things you can grow. Slice it into stir-fries, saute or grill it, shred it into fritters and quick breads, or spiralize it into noodles. Patty-pans are wonderful stuffed and roasted, and small tender squash need little more than a hot pan and olive oil. The blossoms are edible too, delicious stuffed and fried. Because plants produce so heavily, it is worth learning to freeze shredded squash or bake it into loaves so nothing goes to waste.

• Blossom drop and no fruit: the first flowers are all male, and later female flowers need bees. If small fruit yellows and rots, pollination failed, so hand-pollinate in the morning.
• Squash vine borer: a plant wilts suddenly and you find sawdust-like frass at the stem base. Slit the stem to remove the grub, or bury the stem to root and use row covers early.
• Squash bugs: gray shield-shaped bugs and bronze egg clusters on leaf undersides. Crush eggs, hand-pick adults, and keep the garden free of debris where they overwinter.
• Powdery mildew: white powder on leaves late in the season. Space plants for airflow, water at the base, and remove the worst leaves; a fresh succession planting keeps you in squash.
• Bitter or tough fruit: usually from picking too late or from drought stress. Harvest young and keep the soil evenly moist.