Growing conditions. Plant zucchini in full sun in compost rich, well-drained soil. Zucchini likes to get its start in the spot where it will grow, but if you want to get a jump on the season, start seed indoors 3 to 4 weeks before the last expected frost in 4-inch biodegradable pots (that can be set directly in the ground at planting time so that the roots are not disturbed). A week before transplanting, harden off seedlings by cutting back on water and lowering the nighttime temperature to 65°F.
Sowing or setting out starts. Zucchini wants warm soil and air temperatures for growing—in the 70s°F is optimal. Zucchini seed won’t germinate in cold soil. Wait until the soil temperature has reached 60°F before direct seeding or setting out starts. Lay down a sheet of black plastic to warm the soil before sowing or planting. Plants started in chilly temperatures may become stunted.
Avoid too much zucchini. You can avoid too many zucchinis at harvest by simply not overplanting. One zucchini plant will produce 6 to 10 pounds of fruit over the course of the season. Stagger plantings so that you have a continuous harvest but are not overwhelmed.
Spacing. Space plants 2 to 4 feet apart to provide air circulation and discourage disease. A good planting strategy is to plant zucchini on low hills that easily warm in spring. Sow three seeds to a hill and when seedlings have one true leaf, thin the starts to one per hill—just snip off the weakest plants with scissors so as not to disturb the roots of the one that remains.
Pollination. Zucchini is a monoecious plant, meaning each plant has both male and female flowers. A female flower has a small swelling (the ovary) at the base of its short-stem. A male flower has a long, thin stem—and is usually larger than the female. Bees and insects must visit the male flower then the female flower for pollination.
Cross pollination. Do squash plants easily cross pollinate? Yes! But cross-pollination affects next year’s crop, not this year’s crop. If you grow zucchini from newly purchased seed each year, you won’t have to worry about plants cross pollinating. Only if you save seed, should you grow just one variety at a time.
Chilling injury. Temperatures too cold will pit the skin of zucchini. This is called chilling injury. Keep a floating row cover handy to cover seedlings and young plants if the temperature dips below 65°F at night.
Watering. Keep the soil evenly moist. Give zucchini 1 inch of water a week. The critical time for watering is during bud development and flowering. Once plants are established, mulch with straw, hay, or dried leaves to retain soil moisture and suppress weeds. Drought stressed plants are more susceptible to insect attacks.
Feeding. Zucchini are heavy feeders. Prepare the planting bed with lots of organic matter—a few inches of aged compost spread across the bed and then turned under. If leaves grow pale or plants seem weak, side-dress zucchini with well-aged compost or use a foliar spray of liquid fish or kelp fertilizer—high in phosphorus for fruit production. Don’t use a fertilizer too high in nitrogen; it will diminish your yield.
Lots of flowers, no fruit. If your plants are flowering but not producing fruit, there is may not be enough bees around for pollination. Hand pollinate flowers with a cotton swab—gather pollen from the male flower and dab it on to the golden stigma in the center of the female flower.
Harvest. Zucchini should be picked young and tender for the very best flavor. Once fruits are 4 inches long, it’s time to start the harvest. Zucchini can grow 1 to 2 inches a day so check your plants every day at harvest time. Zucchini that grows very large will be pulpy, seedy, and bitter flavored.
Cucumber beetles. Cucumber beetles emerge from dormancy in spring before the weather is warm enough for cucumbers or zucchini to begin growing. When zucchini starts growing, cucumber beetles will begin feeding on leaves and fruits. Check cucumber beetles–little yellow beetles with stripes or spots–with yellow sticky traps or cover plants with a floating row cover, but be sure to remove the cover when flowers appear and it’s pollination time.
Squash vine borers. Squash vine borers (the larvae of wasp-like moths) bore into zucchini stems and eat their way through stems. Look for sawdust-like excrement near small holes to know they are present. Plants suddenly wilt and may die. Slit the damaged vine with a sharp knife and remove the borers with a tweezers. Cover the damaged section with well-aged compost and the plant will grow on.
Blossom-end rot. Irregular watering and a soil calcium deficiency can result in poor water uptake that will result in the blossom end of the fruit (opposite the stem) becoming leathery and sunken; this is called blossom-end rot. Use ground oyster shells or a calcium-rich fertilizer to counter blossom-end rot.
Zucchini Varieties to grow:
- Ambassador: cylindrical, dark green early variety; 50 days to harvest.
- Costata Romanesco: great tasting, nutty flavored Italian zucchini; ribbed, gray-green with pale green flecks; 52 days to harvest.
- Eight Ball: nutty, buttery flavor from dark green globe fruit; 40 days to harvest.
- French White: white fruit on small bushes for small gardens; 50 days to harvest.
- Gold Rush: uniform, cylindrical fruit, AAS winter; 45 days to harvest.
- Spacemiser: high yield from small bush, green fruit can be harvested as baby squash; 45 days to harvest.
- Seneca: dark green, cylindrical fruit on small bush; 42 days to harvest.