When to Plant Carrots: Sow Early, Allow for Slow Seedlings

Sow carrots about 3 weeks before your average last spring frost, once the soil is at least 40°F, and allow 14 to 21 days for them to come up. Finish a spring sowing about 70 days before your normal daily temperature reaches 75°F, and for fall stop about 74 days before your first frost. In Chicago that is March 20 to April 28 in spring and any day up to August 23 for fall; in Dallas it is February 9 to March 5 in spring and about September 16 for fall.

Carrots differ from lettuce or broccoli: they are sown where they will grow, and they are slow to come up, so the soil sets the start date and a crusted seedbed can cancel a sowing. We tested the common counts against NOAA 1991–2020 normals¹ for 37,563 lower-48 ZIP codes, set twelve published local windows beside them, and built dates for 22 cities in spring and 18 in fall. Everything uses air temperature as a stand-in for soil temperature, because our NOAA data has no soil readings.

Spring carrot sowing dates for 22 cities

Published lead times range from none to six weeks. The Old Farmer’s Almanac and Utah State say 2 to 3 weeks before the last frost,^2,7 Colorado State lists carrots as semi-hardy and says 0 to 2 weeks,¹² and Bonnie Plants says 4 to 6.¹⁴ Illinois Extension simply says as soon as the soil can be worked.⁵ Each window below opens on the later of two dates: three weeks before the median last frost, or the day the normal daily mean air temperature reaches 40°F, the soil minimum named by the Almanac and Utah State.^2,7

It closes 70 days before the daily mean reaches 75°F. Colorado State gives 70 days to harvest, Maryland 65 to 75 and Clemson 65 to 75,^12,8,9 and Utah State says carrots grow best when temperatures do not exceed 75°F.⁷ A sowing after that date finishes in the hot weeks, which the heat section covers.

The window is short in the South and long in the North. Charleston has 60 days (January 14 to March 15) and Houston 44, while Austin has 10 and Macon 16. Minneapolis, Boston, Columbus, Portland and Seattle never reach a 75°F normal mean, so they have no heat deadline at all.

Cold: how early is too early

Three weeks before the median last frost, the normal air mean is under 45°F in 28.5% of lower-48 ZIP codes and under 40°F in 1.2%. Bonnie’s six weeks is under 40°F in 47.4%. Maryland says to plant when the soil has reached at least 45°F,⁸ so the 40°F floor we use is the lower of the two published numbers. Using 45°F instead moves our opening date by 0 days in the median ZIP code.

Cold soil also stretches the wait. Utah State says carrots need 14 to 21 days to emerge, Colorado State 10 to 17, and Iowa State and Minnesota say up to three weeks, Iowa State adding that cold soil makes it worse.^7,12,3,13 The cost of going too early is not only a slow start. Utah State answers the question of why a carrot flowers instead of forming a root:

Carrots require cold weather (chilling) to form flowers.

It adds that this can occur if they are planted too early.⁷ The safe habit is to sow at the opening date or later, not before it, and to sow a little every few weeks: Utah State and the Almanac both say every 4 weeks through midsummer, and Iowa State says every 2 to 3 weeks.^7,2,3

Heat: when a spring sowing is too late

Utah State says high summer temperatures reduce growth, decrease quality and cause bitter or off flavors, and that roots turn pale in hot soil when temperatures go above 85°F. Clemson says carrots near maturity in high temperatures tend to develop a strong flavor and roots that are coarse and fibrous.^7,9 We turned that into a deadline: the last sowing whose roots finish before the air mean reaches 75°F.

The test is mostly a deadline for the South and the Plains. Of the 19,615 ZIP codes whose mean reaches 75°F (52.2% of the 37,563), sowing on the median last-frost date finishes late in 23.3%, while the end of the Almanac’s range (two weeks before the last frost) finishes late in only 1.6%. The median window is 27 days; 7.5% have less than two weeks and 36.2% have 30 days or more. The other 47.8% of ZIP codes never reach a 75°F mean, so for them carrots can be sown in succession all summer without a spring deadline.

Slow germination and crusting

Carrot seed is tiny and slow, which is why most failed sowings are not a calendar problem. Iowa State names the usual cause, especially for summer sowings:³

Crusting of the soil surface and dry soil conditions may result in poor germination.

Iowa State says to lightly cover the row with vermiculite, sawdust or peat moss and water gently in dry weather. Utah State says to put the seed on the surface and cover it with compost or fine sand, and Clemson mixes the seed with dry sand and covers it 1/8 inch deep with sawdust, vermiculite or potting soil.^3,7,9 Illinois adds that heavy rain after sowing can pack the surface so that no seedlings emerge, and that clear polyethylene film warms the soil and holds moisture until seedlings appear, when it must come off at once.⁵

Radishes help twice: Iowa State says they germinate quickly to mark the row and to help prevent crusting, and they are harvested in 3 to 5 weeks.³ Do not start carrots indoors; Iowa State says they do not transplant easily, and our indoor seed-starting guide lists root crops as ones to sow in the garden.³

Fall carrots: the last sowing date for a full crop

Published fall counts agree more than spring ones. The Almanac says to start about 10 weeks before the first fall frost, and Maryland says 10 to 12 weeks.^2,8 Iowa State gives a date for central Iowa instead: the last practical planting date is August 1.³ We use 74 days, the same count-back our fall vegetable planting guide uses for carrots (60 days to harvest plus 14 for slow fall growth), which is 10.6 weeks.

Where summers are hot, a second line applies: Utah State says temperatures above 80°F reduce seed germination.⁷ In places whose mean reaches 80°F, we open the window on the day the mean falls back under it.

Only 23.6% of ZIP codes reach an 80°F mean, so most of the country has no heat gate and can sow from midsummer. Where there is one, the heat line and the count-back leave a median of 9 days, and 16.3% have no date that meets both. Austin shows it: the heat line is September 18, 14 days after the count-back date of September 4. Texas A&M’s commercial crop brief says Texas carrots are planted from August to November, which fits sowing into the heat and harvesting in winter.¹⁵

The last date arrives early. By August 1 it has passed in 26.1% of lower-48 ZIP codes, by September 1 in 83.8% and by October 1 in 98.8%; the median last date is August 11. Carrots are hardier than most guides imply, though. Iowa State lists them among very hardy vegetables that take only minor damage below 28 to 26°F, while Maryland calls them semi-hardy and says light frosts are fine but not heavy ones.^4,8 The median 28°F freeze comes 11 days after the first 32°F frost, and a sowing a few weeks past our date still makes small roots.

Leaving carrots in the ground over winter

Three extension sources say mulch lets you keep harvesting. Illinois says a heavy mulch allows harvest throughout the winter in many areas, but also that straw-mulched rows can be harvested until the ground freezes solid. Maryland says fall-planted carrots can be harvested all winter if mulched with straw or shredded leaves before the ground freezes, and Utah State says many gardeners overwinter them under heavy mulch.^5,8,7 Illinois suggests mulch, row cover or a low tunnel to keep snow off, and digging when temperatures are above freezing.⁵

Our January normals show where that works. The January mean is under 32°F in 51.8% of lower-48 ZIP codes and under 20°F in 12.3%, so in half the country expect the ground to freeze for stretches and plan on weeks of mulch harvest, not the whole winter; that is our reading, not a published limit. The January mean is 45°F or higher in 14.5%, where carrots can stay in the garden as a winter crop, as UF/IFAS’s August to March planting range for north and central Florida suggests.¹¹ There is a taste reward: Illinois Extension’s blog says the sweetness is the carrot’s defense against cold.⁶

The carrot produces more sugars to prevent against ice crystal formation in the cells.

Do not leave them past spring. Carrots are biennials, and the Almanac says the tops flower and set seed the next year if you do not harvest.²

What ten sources say about timing and temperature

The published rules are close but not identical, and they sit in different places: some are about soil, some about air, some about frost dates.

Our windows against published local calendars

Twelve published windows from extension services, converted to dates with the NOAA median frost, show where the air-temperature rules help and where they miss.

Our dates are inside or close to the Iowa State, Utah State, Colorado State and Maryland guidance. They are weakest where the published calendars sow into heat: Clemson’s Coastal fall dates start 26 days before our 80°F line in Charleston, and UF/IFAS’s August start is a month ahead of ours in Gainesville, which fits Illinois’s note that midsummer seedlings may need some shade.⁵ For Florida and the Gulf coast, follow UF/IFAS and your county office.

Frost-free ZIP codes and Hawaii

Where a ZIP code has no last-frost date, the frost counts cannot be applied, so use the temperature line only. San Francisco and Los Angeles have a normal mean under 75°F in all 12 months, so heat never closes a carrot window there. Phoenix and Miami are under 75°F only in January to April, November and December: those are the carrot months. Our table has no frost dates for 104 of Hawaii’s 135 ZIP codes, so we give no Hawaii dates; ask your county Extension office.

Next steps

Look up your own frost dates with our frost date lookup and read what a last frost date means. Carrots take a frost better than tender crops, as the frost cover guide shows. They share their early spring window with peas, lettuce, spinach and broccoli. More crops are in our vegetable guides.