When to Plant Zucchini: Frost Dates, Soil Temperature and Fall Sowings

Zucchini and other summer squash go into the garden after the last spring frost, once the soil 4 inches (10 cm) down reads at least 60°F (16°C) at 8 a.m. A reading of 70°F (21°C) is the better target. Across most of the country that lands 1 to 4 weeks after the date when the chance of another spring frost drops to 1 in 10.

The plant has no frost tolerance, and seed sown into cold ground rots instead of sprouting, so a week of patience rarely costs anything. The first fruit comes about 6 to 9 weeks after sowing, so you get more than one chance. A repeat sowing keeps the harvest going when squash vine borers take the early plants, and a midsummer sowing gives a fall crop.

Zucchini planting dates by city

Find the city nearest you: the fourth column is the spring window for sowing seed or setting out transplants, and the fifth is the window for the last sowing that still ripens before fall frost.

Frost dates are medians from NOAA 1991–2020 climate normals for each city's main weather station; in half of years the last frost falls later than the date shown. USDA zones are from the 2023 map.

For any other town, find the spring date after which your chance of a 32°F (0°C) freeze falls to 1 in 10 and sow 1 to 4 weeks after it. For a fall crop, count back 90 to 115 days from your median first fall frost. If you know only your median last frost, start about 3 weeks after it, since the dated spring windows above open 20 to 29 days after that date.

Treat each window as the stretch when the soil is usually ready, and let a thermometer pick the day.

Boston and New York show a soil reading instead of spring dates. Their frost figures come from Logan Airport and Central Park, so a count from them says little about a garden's soil. Sow there by the thermometer, once frost is past and the soil reads 60–65°F (16–18°C).

Short seasons squeeze the calendar. Fargo's spring window runs to June 20 while its fall window opens June 7, so there is one long planting season ending in early July. In Denver the spring window closes on June 16, the same day the fall window opens.

The three Zone 9 cities follow soil warmth and summer heat rather than frost. Sacramento uses the California interior valley months, Seattle sets plants out in early June, and Houston sows in spring on the soil reading and in fall around early October. The regional section below covers each.

How to tell the soil is warm enough

Push a soil thermometer 4 inches (10 cm) into the bed at 8 a.m.: 60°F (16°C) is the minimum for sowing, and 70°F (21°C) is the reading worth waiting for.

The thresholds differ by depth and region, so note both when you compare advice. Short-season northern gardens wait for 70°F (21°C) at 2 inches (5 cm), a stricter test than 60°F (16°C) at 4 inches. Seed germinates fastest near 90°F (32°C) and comes up in 3 to 12 days, sooner in warm soil than in cool.

Soil readings decide the sowing date; air temperature decides how fast young plants grow once they are up.

Where the season is short, warm the bed before you plant. Black plastic mulch laid over the bed before planting raises the soil temperature, and you sow or transplant through slits cut in it. Spun row cover over the seedlings warms the air around them and shields them on cold nights.

Hold off on straw or compost mulch until the soil reaches 75°F (24°C). Those organic mulches insulate the ground and slow its warming, which is the opposite of what a newly sown bed needs.

Zucchini planting times by region

North of the Gulf Coast, frost and soil warmth set one spring window that stretches into summer; in Florida and the low desert, summer heat splits the year into a late-winter crop and a late-summer crop.

A dash means the regional calendar gives no separate late date; use the fall count-back from your own first frost. Texas fall dates are statewide averages for each zone.

Upper Midwest and northern Plains. Cold soil, not frost, holds planting back here, and in northern Minnesota sowing slips into early June. With the median first fall frost as early as September 30 in Fargo, a second sowing has to be in the ground by early July.

Midwest. Sowing can go on any time after frost danger, from spring to midsummer. Plan two main plantings, one for early summer and one in late summer for a fall harvest.

Southeast. South Georgia plants 2 to 3 weeks ahead of middle Georgia in spring and about 2 weeks later in fall; north Georgia runs 1 to 3 weeks behind in spring and about 2 weeks earlier in fall.

Texas and the Gulf Coast. Zucchini grows poorly in cool weather, so spring sowing waits until all danger of frost has passed and the soil holds 60°F (16°C). Fall sowing dates step later as winters get milder, from August 1 in Zone 6, at the state's northern tip, to October 1 to 10 in Zone 9. Those zone dates are statewide averages. The North Texas calendar for the Dallas-Fort Worth area sets fall zucchini at August 1 to 25, earlier than the Zone 8 date of September 10 and in line with the city table. Houston's early-October date falls 60 to 70 days before its median first frost.

Florida and the low desert. Summer squash stalls in the heat of a Florida or low-desert summer, which is why the dates above skip June and July. South Florida's mild winters let one long season run from late summer through spring.

Rocky Mountains. Seed can go in around the average last frost, which is May 5 in Denver, if an 8 a.m. reading at 4 inches (10 cm) already shows 60°F (16°C). Transplants wait until frost is no longer possible. The Denver row opens later, on May 26, because the table counts from the 1-in-10 frost date, the safer choice when you have no soil reading.

Pacific Northwest. Frosts end early around Seattle, but cool springs west of the Cascades hold warm-season crops back. Gardeners there sow indoors in mid-April, set plants out at the start of June and pick from late July through September, using row covers, low tunnels and black plastic mulch to gain warmth.

California. The state's planting months are approximate and shift with local conditions, so lean on the soil test where your site runs warmer or cooler than its region.

How to sow zucchini: depth and spacing

Sow seed about 1 inch (2.5 cm) deep in full sun, then thin to 2 or 3 plants per hill or single plants 18 to 36 inches (45–90 cm) apart.

1. Choose a full-sun spot. Zucchini needs at least 6 hours of direct sun a day and does best with 8 to 10.
2. Sow about 1 inch deep. Press seed about 1 inch (2.5 cm) into the soil. Recommended depths run from 1/2 to 1.5 inches (1.3–4 cm), so anything in that range works.
3. Sow extra seed. Drop 5 or 6 seeds in each hill, or several at each single-plant spot. The spares cover losses to cold soil and early pests.
4. Thin to the final spacing. When the seedlings are 2 to 3 inches (5–8 cm) tall, cut the extras with scissors rather than pulling them, because squash resents root disturbance. Leave 2 to 3 plants per hill or one plant every 18 to 36 inches (45–90 cm).
5. Water deeply each week. Give the bed about 1 inch (2.5 cm) of water a week from rain or irrigation combined. Sandy soil needs water more often in dry weather.

Use the wider spacing for big, bushy varieties and the closer one for open, compact plants.

To fit zucchini into a raised bed or lay out a larger patch, the plant spacing calculator works out how many plants fit at these spacings.

Starting zucchini indoors

Start zucchini indoors only where the season is short or the spring is cool, and sow just 2 to 3 weeks before the date you plan to set plants out.

Direct sowing is the better choice almost everywhere. Squash resents having its roots disturbed, and a transplant set into cold soil grows poorly, so the head start is modest: transplants reach harvest about 14 days sooner than seed sown the day they go out.

Sow in 3-inch (7.5 cm) pots and grow the seedlings with days around 70–75°F (21–24°C) and nights around 60–65°F (16–18°C). Set them out small and young, 2 to 3 weeks after sowing, and slide each root ball out whole. Because the outdoor window opens 1 to 4 weeks after the 1-in-10 frost date, the indoor sowing usually lands near your median last frost. The cool Pacific Northwest is the exception, with a mid-April sowing for an early-June set-out.

Transplants follow the same outdoor calendar as seed, not an earlier one. A seedling set out ahead of the window meets the same frost and cold ground that would have stopped seed, and it cannot be put back in its pot.

Repeat sowings and fall zucchini

Sow zucchini two or three times a season, 2 to 3 weeks apart, so young plants are coming into bearing when the first ones falter.

A simple pattern is to sow part of the row at the start of your window and the rest 3 weeks later. Repeat sowings also keep fruit quality high through the season.

Outlasting squash vine borer

The squash vine borer is the main reason to stagger sowings. The moth lays eggs at the base of the stem, the larvae tunnel inside, and the plant wilts suddenly. In Illinois the adults fly from mid-June into July.

Once a larva is inside the stem, no spray can reach it; Bt works only as a preventive treatment before larvae enter, and any product must be used exactly as its label directs. To save an infested plant, slit the stem lengthwise, remove the larva and heap soil over the wound. Burying a stem joint every foot (30 cm) along a sprawling vine lets it root, so the plant survives even if the base is damaged. At the end of the season, pull spent plants and clear the debris from the bed.

The last sowing for a fall crop

For a fall harvest, make the last sowing 90 to 115 days before your median first fall frost, which is the right-hand column in the city table.

The rule comes from counting back from the frost date. Add the variety's days to maturity, about 18 days of picking, and about 14 days because growth slows as fall days get shorter and cooler. A 47-day variety such as Dunja needs 47 + 18 + 14 = 79 days, so a sowing 90 days out leaves about 11 days of margin, and the 52-day Costata Romanesco needs 84. In half of years the first frost comes earlier than the median, so aim for the first half of the window unless you grow a fast hybrid.

Some state calendars set earlier dates. Maryland puts its second crop in from July 1 to 15, and in Georgia the last planting date is August 31 in the middle of the state and about 2 weeks earlier in the north. If your state's calendar gives an earlier date than the table, follow it.

In the Southeast, choose varieties labeled resistant to downy mildew for the last sowings of summer. Once the vines come out, the bed is free for a cool-season crop, and garlic planting times show what can follow.

Varieties that change the timing

Seed catalogs list zucchini at 42 to 52 days from sowing, a 10-day spread that matters most for late and short-season sowings; in a home garden, allow 45 to 65 days.

Days count from direct sowing in seed-catalog trials; take off about 14 days for transplants.

For Fargo-style short seasons and for the last sowing anywhere, a 42- to 47-day hybrid gives you more weeks of picking before frost than a 52-day heirloom. Costata Romanesco is an Italian heirloom grown for its flavor, and it suits an early sowing that has the whole summer ahead of it.

Some hybrids are parthenocarpic, meaning they set fruit without pollination. Check the seed packet, because those can stay under row cover all season.

Planting too early or too late

Planting too early usually costs more than planting late: seed rots in cold soil and one frost kills the plants, while a late spring sowing mostly costs picking days.

Seed in soil still below 60°F (16°C) is likely to rot, and transplants set into cold soil stall, so an early start buys frost risk without a reliable gain.

Late sowings have their own costs. In the South, late plantings face more vine borer and pickleworm, and in Florida and the low desert a sowing pushed into summer meets heat the plants cannot grow through. A fall sowing made too close to frost leaves fruit unripe when the first killing frost ends the crop.

If a late frost is forecast

Lay spun row cover over the plants in the evening and weigh down the edges. A light or medium cover holds off about 4°F (2°C) of frost, enough down to about 28°F (−2°C); on a colder night, expect losses. Leave it in place until the danger passes, but remove it once the first flowers open so bees can reach them. If frost does kill the seedlings, sow again at once: with harvests 45 to 65 days from seed, there is still time for a full crop almost everywhere.

What to expect after sowing

Seedlings come up in 3 to 12 days, the first flowers open a few weeks later, and the first fruit is ready about 6 to 9 weeks after sowing.

Zucchini carries separate male and female flowers on the same plant, and bees carry pollen between them. Where few bees visit and fruit set is poor, move pollen by hand from a male flower to a female one, which has a small fruit at its base. Male blossoms can be picked for the kitchen without cutting the yield.

Fruit is ready 4 to 8 days after its flower opens. Pick elongated zucchini at 6 to 8 inches (15–20 cm) long and 1.5 to 2 inches (4–5 cm) across, or as small as 4 inches (10 cm) for tender fruit. A rind too hard to dent with a thumbnail means the fruit is over-mature. Check the plants daily once they bear and pick every 2 to 3 days.

To plan zucchini alongside the rest of your warm-season crops, see tomato planting times, pumpkin planting times, cucumber planting dates and vegetable planting dates, then add your sowing dates to Sow's garden calendar.