Zucchini

Zucchini, also called courgette, is a type of summer squash (Cucurbita pepo). Like other summer squash, it’s a warm-season crop that grows best at average temperatures between 65 and 75 °F (18–24 °C), and it’s very tender: frost damages the plants.

Summer squash plants are generally bushy rather than vining, though some zucchini varieties form large trailing plants while others stay compact. They crop heavily: in good weather, one plant can give three or four fruits a week.

Wait until it’s warm. Squash seeds don’t germinate well in cold soil. Don’t plant until the last chance of frost has passed and the soil is 60 °F (16 °C) at 4 inches (10 cm) below the surface. Gardening experts wait for soil of 65 °F (18 °C).

Sow outdoors or start indoors. You can plant seeds or transplants. For a head start, sow indoors in 3-inch (7.5 cm) pots about 3 weeks before planting time, and handle the young plants gently so the roots are disturbed as little as possible. Indoors, sow each seed on its side about ½ inch (13 mm) deep; the seeds need 18–21 °C (65–70 °F) to germinate.

Sowing depth outdoors. Sources differ: gardening experts sow ½ inch (13 mm) deep, gardening experts 2.5 cm (1 in) deep, and gardening experts 1 to 2 inches (2.5–5 cm) deep.

Give plants room. Zucchini plants get big. Gardening experts allow about a square meter (roughly 11 square feet) for each plant and spaces them at least 90 cm (3 ft) apart. Gardening experts thin seedlings to 12 to 15 inches (30–38 cm) apart in rows 3 feet (90 cm) apart.

Choose full sun. Grow zucchini in full sun: at least 6 hours of direct sun a day, and ideally 8 to 10.

Growing in pots. Choose a compact or bush variety and a container at least 45 cm (18 in) wide, with one plant in the middle, and keep it in a warm, sunny spot. A growing bag can hold one or two compact plants.

Watering. Zucchini are thirsty plants. Keep the soil consistently moist, especially in containers and while the plants are fruiting; in hot weather, pots may need watering every day. The most important time for moisture is while fruit sets and develops. Water around the base of the plant rather than over the leaves, because wet leaves encourage powdery mildew.

Feeding. Don’t overdo nitrogen: it gives lots of leafy vine and less fruit. Plants in the ground don’t usually need feeding unless the soil is poor. In containers, feed every 10–14 days with a high-potash liquid fertilizer once the first fruits start to swell.

Mulching. A 2 to 3 inch (5–8 cm) mulch of grass clippings, pine straw or leaves stops the soil drying out quickly, which helps prevent blossom-end rot.

Pollination. Zucchini have separate male and female flowers, and bees must carry pollen from one to the other. Poor pollination means misshapen fruit or none at all. Plants usually produce only male flowers for the first week or two, which is normal.

Common insect pests include spotted and striped cucumber beetles, squash bugs, squash vine borers, pickleworms and aphids. Vine borers can make a whole plant collapse, and aphids spread viruses. Powdery mildew and viruses are common diseases, along with downy mildew, bacterial wilt and phytophthora; good drainage, airflow, pest control and crop rotation help prevent them. Slugs and snails may eat young plants, flowers and young fruit.

Blossom-end rot is a dark, dry rot at the flower end of the fruit, caused by a lack of calcium in the developing fruit. In cool early-summer weather, fruits may also rot while very small because of poor pollination; this usually sorts itself out once the weather improves.

Gardening experts put zucchini at 50 to 65 days from transplanting to harvest. Pick the fruits young and tender, about 6 to 8 inches (15–20 cm) long, or smaller, at 10–12.5 cm (4–5 in), for the best flavor. Check plants daily once they start bearing, and don’t leave large fruits on the plant, because they hold back new ones.

The flowers are edible too. Pick male flowers (the ones without a small fruit behind them), so you don’t reduce the crop.

Store zucchini in a plastic bag in the refrigerator for up to a week. In cool, humid conditions of 32–50 °F (0–10 °C), they keep for 5 to 14 days.

Pet poison experts list zucchini as non-toxic to dogs and cats.