When to Plant Sweet Corn: Soil Temperature, Dates by Frost and Succession Sowing

Two things decide when sweet corn goes in: soil temperature and the type of corn on the seed packet. Old-fashioned sugary varieties will come up in cooler soil than the newer supersweets, which have small, shriveled seeds that rot easily in cold, wet ground. After that, corn timing is mostly about spreading the harvest out, because a single planting ripens over just a few days.

Step 1: check the soil, not the calendar

A soil thermometer pushed about 4 inches deep settles it. Extension guidance, by type:

Cold soil is the main risk. Clemson says planting in wet early-spring soil promotes seed rot, and UMN notes diseases infect seeds more easily in cool soil; if you use untreated seed, UMN says to wait until the soil is at least 65°F. UMD suggests pre-germinating seed before planting in cool spring soil to help avoid rot and seed-corn maggot.

Step 2: dates by last frost

Our planting calendar gives sweet corn an outdoor window from your average last spring frost to about four weeks after; Texas A&M's vegetable table says 1 to 6 weeks after the frost-free date. Start supersweets toward the later end. The succession column shows three follow-up sowings two weeks apart (UMD), counted from your frost date.

Regional examples: Clemson lists spring planting from March 30 to May 31 in South Carolina's Piedmont and March 1 to April 15 on the coast. In Minnesota, UMN's guidance is simply to wait for warm soil, usually late spring.

Step 3: plant in rounds for a longer harvest

A planting of sweet corn ripens all at once, and sugary types lose sweetness quickly after picking (UMN), so most extension guides suggest more than one sowing:

• Repeat sowings: every two weeks or when the previous planting has three to four leaves (UMD); every 10 to 14 days (Clemson); when the first plants have three to five leaves, usually 2 to 3 weeks (Texas A&M).
• Mix maturity dates: plant early-, mid- and late-season varieties on the same day (UMD, Clemson).
• Late sowings: UMD says to use only the quickest-maturing varieties for July plantings.

Step 4: keep types apart

Supersweet corn crossed with other types gives starchy, tough kernels (UMN). Separate them by distance or time: UMD says 400 yards or two weeks between plantings; Clemson says 400 yards or maturity dates one month apart; UMN says not less than two weeks of difference and, near farm fields, about 300 feet from field corn. In a home garden, the simplest fix is to grow one type, or to stagger plantings so they don't shed pollen at the same time.

The last sowing date

Sweet corn needs about 70 to 90 days (Texas A&M) or 80 to 95 days (Clemson), depending on variety, and it is killed by frost. To find your latest sowing, count the packet's days to maturity back from your average first fall frost, as below. This is simple arithmetic, so leave yourself a margin: growth slows as fall nights cool, and Texas A&M's own fall rule is 12 to 14 weeks before the first frost.

Texas and Florida dates

Texas A&M AgriLife's fall vegetable guide lists sweet corn by region; the spinach column is included for comparison with our spring spinach guide:

University of Florida IFAS lists sweet corn from seed in March and April in North Florida, January through April in Central Florida, and October through March in South Florida.

Planting depth, spacing and harvest

Where corn goes in the garden

Corn is the tall backbone of the Three Sisters with beans and squash. See what to plant with corn for companions, the Three Sisters garden guide for the mound method, and succession planting for fitting repeat sowings into the season.

Frequently asked questions

What soil temperature does sweet corn need?

Clemson says not below 50°F at a 4-inch depth, and above 55°F reduces seedling rot; UMN says seed germinates best near 60°F. Supersweet (sh2) varieties need about 65°F (UMD, Clemson).

How soon after the last frost can I plant sweet corn?

Once the soil is warm, usually from your last frost date to a few weeks after. Texas A&M lists 1 to 6 weeks after the frost-free date.

How often should I plant sweet corn for a continuous harvest?

Every 10 to 14 days (Clemson), every two weeks or when the previous planting has three to four leaves (UMD). Or plant early, mid and late varieties at the same time.

Can I plant supersweet corn next to regular sweet corn?

Not if they will pollinate at the same time. UMD advises 400 yards or two weeks apart; Clemson says 400 yards or maturity dates a month apart. Crossing makes starchy, tough kernels (UMN).

What is the latest I can plant sweet corn?

Count the days to maturity back from your first fall frost and leave a margin. UMD says to use only the quickest-maturing varieties for July plantings; Texas A&M gives 12 to 14 weeks before the first frost for fall corn.

How deep should I plant sweet corn?

About 1 inch deep (UMN, Clemson). Supersweet seed should go no deeper than ¾ to 1 inch and be kept moist until it sprouts (UMN).