When to Plant Zucchini

Spring planting: wait for warm soil

Zucchini is frost-tender and germinates poorly in cold soil. Clemson plants once the soil reaches 60°F at a 4-inch depth, and Utah State waits for 65°F. Colorado State’s vine-crop rule is to delay at least a week after the average last frost, longer if the weather is chilly. In most areas that puts spring planting 1 to 3 weeks after the frost date, which is where the dates for your zone above begin.

Iowa State gives a regional example: summer squash is sown in mid-May in central Iowa. Use a soil thermometer in mid-morning and look for several days in a row at or above 60°F before sowing.

Getting an earlier start

Two methods gain time in spring. Transplants started indoors 3 to 4 weeks before your planting date, in peat pots or other plantable containers, give an earlier first picking (Iowa State). Harden them off for a few days before setting them out. Black plastic mulch laid over the bed warms the soil, and combined with row covers it lets you plant 2 to 3 weeks before the last frost date (Utah State). Vent covers when it gets above 80°F underneath and remove them once flowers open so bees can pollinate.

A second crop in midsummer

Zucchini is fast: plants flower 35 to 45 days after sowing, according to Utah State, and each fruit is ready 3 to 5 days after its flower opens. That speed makes a second planting practical almost everywhere. Spring plants tend to slow down by late summer, and the University of Nebraska notes that midsummer sowings of summer squash give vigorous plants that bear up to the first frost.

To find your last sowing date, count back from your average first fall frost the variety’s days to harvest, plus about 14 days for slower growth in shorter, cooler days, plus 14 more because the crop needs to mature at least two weeks before frost (Nebraska’s method). For 40- to 55-day zucchini, that is about 10 to 12 weeks before the first frost. Iowa State’s last practical sowing date for central Iowa is July 20.

Timing around squash vine borers

Where squash vine borers are common, they often decide how long a spring zucchini planting lasts. The adult moths emerge in late spring and early summer and lay eggs at the base of the stems. Iowa State notes that a crop planted in late June or early July, after egg-laying is over, can escape much of the damage, and that this works for zucchini because it matures in well under 90 days. UConn agrees that delayed planting is most successful with fast-maturing summer squash. UConn also cautions that the tactic works less well where the growing season is short.

Cover fall plantings with row covers while they are young: Nebraska warns that squash bug and cucumber beetle numbers peak in August and can destroy seedlings.

The South and desert Southwest

In the Southeast, zucchini fits a long spring window and a late-summer one. Clemson plants from April 15 to July 31 in the South Carolina Piedmont and March 15 to July 31 on the coast, with fall plantings from July 15 to August 15 in the Piedmont and through August on the coast.

In the low desert around Phoenix, the University of Arizona sows summer squash from mid-February to early April and again from mid-August to early September, skipping the hottest part of summer.

Warm-winter zones 9 to 11

In frost-rare areas, zucchini is a cool-season crop. UF/IFAS plants summer squash in late March to April and again in August to September in North Florida, January to April and August to September in Central Florida, and from August all the way through March in South Florida.