When to Plant Potatoes: Spring Dates and Soil Temperature by City

Plant potatoes about two to four weeks before your average last spring frost, once the soil 4 inches down has reached about 45°F. In most of the US that falls between early March and late April: about March 7 in St. Louis and Washington, D.C., March 28 in Chicago and April 12 in Minneapolis.

Most guides give one of those two rules and stop. We tested them against each other with 12 springs of measured soil temperature from 28 NOAA stations. At the typical station, 4-inch soil reached 45°F 26 days before the median last frost, so the rules usually agree. But at a single station the soil date moved by a median of more than five weeks from one spring to the next, which is why a soil thermometer beats the calendar.

Potato planting dates for 22 US cities

Each window starts on the later of two dates: four weeks before the median last frost, or the day the soil 4 inches down typically reaches 45°F. It runs for two weeks. Frost dates come from NOAA’s 1991–2020 normals for the station nearest each ZIP code.¹ The soil date is our estimate from those normals, explained in the next section.

The last column matters because potato shoots come up two to four weeks after planting, depending on soil temperature, according to Cornell.⁵ Until the 10% date, there is still about a one-in-ten chance of a frost on them. For any other ZIP code, look up your frost dates and their odds, then count back four weeks from the median date.

The two rules: weeks before frost, or soil temperature

Extension services agree on the idea but not the numbers. On the calendar, Cornell says two to four weeks before the last frost,⁵ Utah State says 14 to 21 days⁶ and Texas A&M says about three weeks.³ On soil temperature, Cornell’s minimum is 40°F,⁵ the University of Maryland, South Dakota State and UGA Extension in Colquitt County use 45°F,^7,12,13 and Utah State and Texas A&M use 50°F. The Texas A&M fact sheet gives the depth too:

Plant potatoes when the soil temperature 4 inches deep reaches about 50 degrees F

The same fact sheet offers “about 3 weeks before the last spring frost” as the alternative, as if the two dates were the same. Our measurements say they often aren’t.

What 12 springs of measured soil show

NOAA’s U.S. Climate Reference Network records soil temperature at 4 inches (10 cm) at open, rural sites.² We took 2014–2025 data from 42 stations and found the first day each spring that the five-day average reached 40, 45 and 50°F, then compared it with the NOAA median last frost for the nearest ZIP code. At 45°F, 28 stations had usable dates. Thirteen, from Kentucky and Virginia south, were left out because their soil was already that warm in early February in at least one spring, and one in Alabama had too few complete springs.

Three findings stand out:

• The 45°F rule and the calendar rule usually agree. The median station reached 45°F 26 days before the median last frost, and 23 of 28 stations reached it at least two weeks ahead.
• The 50°F rule is later. At the typical station, the soil had reached 50°F three weeks before the frost date in only one spring in three. Planting “about three weeks before frost” usually means planting before Texas A&M’s 50°F.
• The far north is the exception. In northern Minnesota, North Dakota and Maine, 4-inch soil reached 45°F within about a week of the median last frost, and one Minnesota station did so after it. There, wait for the soil.

Across 30,706 ZIP codes with regular spring frost, our estimate puts 45°F soil at or before the middle of the two-to-four-week window in 76% of them. It lags by more than a week in about 7%, mostly in New York, Maine, Minnesota, Massachusetts and New Jersey, where cool springs follow a fairly early frost date.

How to check your own soil

Push a soil thermometer to planting depth, about 4 inches. Our dates use a five-day average, so one warm afternoon doesn’t count. Normals describe a typical spring, and the soil date at a single station moved by a median of 37 days between its earliest and latest springs. Cold, wet soil is the real risk: seed pieces can rot if planted into prolonged cold weather, warns the University of Maryland.⁷ The same soil-warming method drives our guide to when to plant grass seed in spring, and the methodology page explains the frost data.

Why frost still matters after planting

Potato tops can’t take frost, though the plants often recover. Cornell notes that late spring frosts can damage the foliage, but growth usually rebounds.⁵ LSU AgCenter says light frosts won’t harm the plants, while hard freezes may hurt the tops and delay harvest.¹⁷ Recovery has limits. Texas A&M warns that plants killed by a late frost will not come back if the seed piece has rotted,³ and organic grower Alley Swiss told A Way To Garden that each regrowth means a smaller, later harvest.²⁰

That is why Table 1 shows the 10% last-frost date. Plant at the start of the window and shoots typically appear around the median last frost, when a frost is still a coin flip. If one is forecast once they are up, cover them for the night.

How our dates compare with local extension calendars

We lined our windows up against 12 published local calendars. Seven fall fully or mostly inside the published window: all three Iowa regions, central Illinois, Maryland, Dallas and north Florida. The misses go both ways:

Sources: University of Minnesota,⁴ Iowa State,⁸ Illinois,¹¹ Maryland,⁷ Clemson,¹⁵ NC Extension in Pender County,¹⁶ Oregon State,¹⁹ Texas A&M,³ LSU AgCenter¹⁷ and UF/IFAS.¹⁸ Where your county publishes a date, follow it.

Two patterns explain most of the gaps. In the Southeast, calendars plant five to seven weeks before the median last frost, when the soil is already warm and only the tops are at risk. In the Pacific Northwest, Oregon State waits for daytime temperatures of 60°F, so its Willamette Valley window runs late March through May, after the median frost date.¹⁹ Minnesota is the third gap. The University of Minnesota’s advice is simple:

Plant tuber pieces as soon as the soil warms

It puts that at early April in the Twin Cities, a week or more before our April 12 soil estimate for downtown Minneapolis. NOAA’s soil stations sit on open, rural ground, and a sheltered city garden can differ.

Southern winter planting and fall potatoes

Where winters are mild, extension services plant in winter so the crop finishes before summer heat. Tubers stop forming when the soil reaches 80°F, says the University of Illinois.¹⁰ Texas A&M and LSU AgCenter also recommend a fall crop; Clemson advises against one in South Carolina because of pests and disease.¹⁴

Windows: Texas A&M,³ LSU AgCenter,¹⁷ UF/IFAS,¹⁸ Clemson¹⁴ and NC Extension.¹⁶ The NOAA columns are our calculation.

Fall potatoes: count back 110 days from the first frost

Texas A&M’s rule is to plant a fall crop about 110 days before the first expected frost, or mid-August in most of Texas, using small, uncut potatoes because they resist rotting in hot weather better than cut pieces.³ It notes that many gardeners buy extra seed potatoes in spring and hold them for fall planting. The same count-back from the first frost sets the deadline for other fall crops; see our fall vegetable garden planting dates.

How late can you plant potatoes?

Later than most calendars suggest, if the crop has time to finish before heat or frost. The University of Illinois says midseason and late varieties may be planted as late as July 1, and that medium-early plantings in dried, warmed soil may do as well as very early ones.¹⁰ New potatoes can be dug about seven to eight weeks after planting, says the University of Minnesota.⁴ For a late crop, straw mulch keeps the soil about 10°F cooler, according to Illinois.¹⁰

How to plant seed potatoes

1. 1

   Buy certified seed potatoes

   Grocery potatoes may be treated to stop sprouting or may carry disease, say the University of Minnesota and Iowa State.^4,9 Small potatoes can go in whole.

   

2. 2

   Cut and cure larger tubers

   Cut big seed potatoes into chunks of about 1¼ inches, each with at least one eye and preferably two or three. Leave them at 60–70°F for a few days so the cut surface dries and toughens.⁴

3. 3

   Plant 3 to 5 inches deep

   Set pieces cut side down, 10 to 12 inches apart, in rows 30 to 36 inches apart, and cover with about 4 inches of soil.⁴

   

4. 4

   Hill as they grow

   Once shoots emerge, pull soil up around the stems. Hilling keeps shallow tubers out of the light, which turns them green.⁴

Potatoes are one of the earliest crops in the garden. For the rest of the spring plan, see when to start seeds indoors and when to plant tomatoes, which go out weeks after your potatoes. In fall, garlic goes in around the time late potatoes come out. Our guide to what a last frost date means explains the 10%, 50% and 90% odds, and the vegetable guides cover more crops.