There is no single best carrot planting month for every garden. You get two good windows each year instead. Sow in spring once the soil warms up. Then sow again in late summer for an autumn harvest. The exact month depends on your climate far more than the date on the calendar.
I was kneeling at my raised bed of sandy loam in early April. I pressed a fingertip into soil that had finally warmed past 45°F (7°C). That reading was my green light for spring, so I dropped the first seeds in that morning. Months later I knelt at the same bed in midsummer. I sowed a second round into much warmer ground for a later crop. The two sowings landed weeks apart because the soil told me when, not the month.
Carrots are a cool-season crop. They sprout and grow best in mild, settled soil. For spring carrot planting, wait until the soil reaches at least 45°F (7°C) before you sow. Cold, soggy ground rots the seeds and leaves you with thin, patchy rows. A cheap soil thermometer takes the guesswork out of the whole job. I push mine in about an inch and check it for two mornings before I commit any seed.
In many temperate regions that spring window falls between March and May. Gardeners in warm southern zones can start as early as February. Cold northern areas may need to wait until late May or even early June. Your local last-frost date is a better guide than any fixed month. Carrots handle a light frost without trouble, but young seedlings still want calm, mild weather to settle in and root. My own first-frost date sits in mid October, so I treat late July as my hard deadline for the second round.
Timing matters even more for the second sowing. Hot midsummer soil works against you here. Heat above 85°F (29°C) stalls germination and dries out shallow seeds in a hurry. Aim your summer sowing for July or August in most regions. Pick the cooler end of that range if you can. Keep the seedbed damp every day until the seeds break through, and shade the row with a board or burlap if the sun is harsh.
Now for the math that makes autumn work. Count back 10 to 12 weeks from your first expected frost, then sow. That window is the one University of Maryland Extension points to. The roots need that full stretch of mild weather to size up before the cold sets in. Sow too late and you end up pulling skinny, stunted carrots in November. Sow on time and the roots fill out while the days are still gentle. I lost a whole row one year by sowing in mid September, and they never got past pencil width.
Here is the payoff for that second round. Carrots taste sweeter after a light frost, which makes fall carrots worth the extra planning. Cool nights push the roots to store more sugar as a kind of natural antifreeze. You can leave them right in the ground and pull them as you need them. A thick layer of straw mulch keeps the soil workable, so you can harvest crisp roots well into early winter in many areas.
So skip the rigid calendar and let your local frost dates set the schedule. The right carrot planting month is simply whichever one matches your soil and your frost dates. Check the soil temperature in spring before you put any seed down. Then count back from your first frost in late summer for the fall crop. Adjust earlier in warm regions and later in cold ones, and write both dates on a tag stuck right in the bed. Do that and you can harvest sweet, crisp carrots from two plantings every single year.
Read the full article: Carrot Growing Guide: Seed to Harvest
