Zucchini and squashes are tender plants which need heat to germinate, so are best sown indoors in mid- to late spring, right about when the last frost is expected. Sow single seeds 1 in (2 cm) deep into cells or small pots filled with potting mix, water well, label, and cover with a clear plastic bag or a lidded propagator and place on a warm windowsill.
Direct outdoor sowing into soil improved with plenty of organic matter is possible in early summer. Place two seeds into one hole 2 in (5 cm) deep at stations 3 ft (90 cm) apart. Cover with soil, water, then protect under a cloche for additional heat.
PLANT OUT: Before transplanting, prepare the soil for these hungry plants by incorporating plenty of well-rotted manure or compost. Create a mound of soil about 6 in (15 cm) high on heavy soils to aid drainage. Harden off plants by acclimating them to outdoor conditions over 2—3 weeks. Zucchini and squashes can also be grown in large containers or grow bags.
Space plants 3 ft (90 cm) apart; place them in the soil at the same depth as they were growing in their pots, firm the soil gently around their roots, and water. Cover with cloches to protect their delicate stems from breezy conditions.
WATER AND FEED: These soft plants are prone to stem rots, so only water them in dry weather or if growing in sandy soil. Plants grown in pots, however, will need frequent watering—daily or even twice daily in summer—to support their rapid growth. Feed container grown plants with a liquid tomato fertilizer twice a week after their first fruits have formed. Plants growing in the open soil only need feeding if they are not growing vigorously.
POLLINATE: Zucchini and squashes produce separate male and female flowers, and insect pollination needs to occur for fruits to form naturally. Yields can be improved, particularly in cold or wet spells of weather, by hand pollinating the female flowers, which have a small, immature fruit below them. Do this by picking an open male flower with a long, thin stem, removing its yellow petals and pushing it into the center of a female flower.
Zucchini and summer squashes taste best when young. Harvest by twisting or cutting from the plant. Picking when young encourage the production of more flowers and fruits, and avoids having to deal with gigantic watery marrows later in the season.
For large winter squashes, limit each plant to three fruits by pinching out the growing tips of plants and removing all unwanted flowers. Winter squashes should be left on the plant to develop. At the end of summer, remove any leaves shading the fruit and allow their skin to harden in the sun. Harvest before the first frost by cutting, leaving a length of stem attached. Store in a dry, frost-free place and they will keep for several months.