Idaho · zones 5b–7b
When to plant carrots in Idaho.
Sow between Apr 3 to May 6 in a typical year, keyed to Idaho's median last frost around May 11. A second, fall sowing fits Jul 3 to Jul 29. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Carrots dates for a typical Idaho season.
Direct sow
Apr 3 to May 6
Keyed to the ~May 11 last frost. Sow 0.25" deep, 2" apart.
Fall round
Jul 3 to Jul 29
Counted back from the ~Sep 28 first frost.
Harvest
~68 days later
~0.2 lb per plant over ~2 weeks.
Idaho spans more than one climate: Zone 6 is the most common zone, but the state runs 5b to 7b. That's why the planner works from your ZIP code's frost dates, not your zone: mountain and coastal gardens in the same state can be three weeks apart.
Idaho growing notes
A carrot root here is only as straight as the ground it grows in, and Idaho's deep valley loam is about as good as that ground gets.
The soil decides the shape before the seed does
Carrots go into the ground directly, sown a quarter inch deep and thinned to about 2 inches apart, and reach harvest size in around 68 days, well inside the state's roughly 140-day frost-free run. What decides how that root turns out has less to do with the calendar than with what sits under it. A carrot can only push through soil it can move, and the Treasure Valley's deep, fine loam lets it do exactly that: roots come out long, straight, and about as good as this crop gets anywhere in the state.
Higher, rockier ground tells a different story. A root that meets a stone, a clay lens, or compacted soil doesn't stop; it forks into two or three legs or twists around the obstacle and comes up stubby instead of straight. Pulling one test root partway through the season answers the question before the whole bed gets dug: a forked or stunted root that early is the soil talking, not a sign the planting needs more water or feed. Working the bed a full spade deep before sowing, and picking out stones as they turn up, matters more than anything added after the seed goes in.
Choosing the shape that matches the ground
A long, tapered Nantes type, Scarlet Nantes is the classic example, rewards exactly the deep, loose loam described above, running its full length without resistance. Where the ground runs shallower or stonier, which describes a fair amount of high-country soil and plenty of ordinary yard dirt, a shorter, blunter type such as Danvers or Chantenay reaches the same roughly 68-day finish line while tolerating heavier ground that would fork a longer root. The choice comes down to what is already in the bed, not what a gardener wishes were there.
A lot of the state's irrigated ground also tests toward the alkaline side. Carrots tolerate that better than some vegetables do, but working an inch or two of compost into the bed before sowing loosens heavy ground. At around a fifth of a pound per root, filling a kitchen's carrot bin takes real row footage, and four separate sowings fit into a single season here, spaced a few weeks apart through spring and again in late summer for a fall root.
Four things that go after the roots and the tops
Carrot rust fly is the one that does real damage: the adult tucks her eggs into the soil right beside a young seedling, and within days the hatched grubs are already boring straight down into the taproot, a wound that stays hidden until harvest pulls up a carrot laced with rusty tunnels. Cool, damp air draws this fly in, which makes the northern panhandle's wetter climate a bigger risk than the drier valley floor, and a fine mesh cover left in place from sowing through most of the season keeps the adult from ever reaching bare soil to lay in. Parsleyworm goes after the foliage instead of the root: the green, black-and-orange-banded caterpillar strips the ferny tops as the larval stage of a swallowtail butterfly, and the orange forked horn it flashes when disturbed looks worse than it actually is.
Aphids cluster on the same ferny foliage and rarely amount to more than a light water spray can handle. Alternaria leaf blight shows up as dark, ragged spots starting at the leaf tips and working inward, spreading fastest on foliage that stays wet, which makes watering at the soil line instead of overhead the simplest way to keep it from getting much further.
In Idaho: watch for
The pests that find carrots here.
The short season here, about 140 frost-free days, keeps carrot in front of carrot rust fly only briefly. One early row cover usually carries a planting through the worst of it.
Rusty tunnels in the roots and stunted tops.
Organic fix: Cover the row; rotate away from last year's carrots.
Big green-and-black striped caterpillars on the foliage.
Organic fix: Handpick (or leave for swallowtails); Bt if heavy.
Brown spots ringed in yellow on the oldest leaves first, darkening until the tops look scorched.
Organic fix: Water at the base rather than overhead, turn under old carrot tops, and leave 2 years between carrot crops.
Your season math: Idaho gives carrots about 140 frost-free days, and it needs roughly 68 days to a first harvest. That fits about 4 re-sown rounds across the season, so you can keep it coming instead of picking once.
Planting carrots in Idaho: questions
When should I plant carrots in Idaho?+
In a typical Idaho year, sow carrots between Apr 3 to May 6, keyed to the state's median last frost around May 11. There's also a fall window: Jul 3 to Jul 29. Your exact dates shift with your ZIP code and microclimate.
What USDA zone is Idaho?+
Idaho spans zones 5b–7b, mostly zone 6. But frost dates, not zones, set planting time. The free planner uses your ZIP code's actual frost dates.
How many carrots plants do I need?+
Depends who you're feeding. The crop page has exact counts per household size, or the free planner does the math for your family in about 60 seconds.