When to plant carrots in zone 6a

Sow outdoors between Apr 14 and Apr 28. That is from 2 wk before to on the zone 6a's median last frost, Apr 281. Across most of zone 6a that date falls between Apr 2 and May 10.

Why a range: zone 6a is defined by winter lows, not frost dates. Its ZIP codes have median last frosts from Apr 16 to May 102, so a single zone date can be weeks off for you. The rule comes from Colorado State University Extension, written for CO and applied here to zone 6a's frost dates.

Last reviewed: 2026-11-02
Stations: 924
ZIP codes: 4,375

Photo: Markus Spiske / Pexels

These dates use the typical last frost for the whole zone. Your ZIP code gives a closer answer.

Sow outdoorsColorado StateSow outdoors across most of the zone: Apr 2 to May 10Sow outdoors at the zone median: Apr 14 to Apr 28 (Colorado State)

Start indoors
Plant outdoors
Range across the zone
Frost-free season (median)
Spring frost risk (90% to 10%)
Fall frost risk (10% to 90%)

Figure 1. Carrots in zone 6a. Dark bars: at the zone's median frost dates. Pale bars: across most of the zone's ZIP codes. Hatched blue: where the zone's last and first frosts fall.

Sow outdoors: Apr 14range Apr 2 – May 10

What each source says, applied to zone 6a

The same frost dates give different answers depending on whose rule you follow. These are all the published rules we hold for carrots, worked out at zone 6a's median frost dates.

Table 1. Carrots rules from every source, at zone 6a's median last frost (Apr 28) and first frost (Oct 17).
Source	What	Rule	Zone 6a median
Colorado State1Used above	Sow outdoors	From 2 wk before to on the last frost	Apr 14 – Apr 28
Utah State3	Sow outdoors	2 weeks before last frost	Apr 14
Oregon State, eastern OR4	Sow outdoors	4 weeks before last frost	Mar 31
Texas A&M (E-502)5	Sow outdoors	4-6 weeks before last frost	Mar 17 – Mar 31
Texas A&M (E-502)5	Plant for fall	12-14 weeks before first frost	Jul 11 – Jul 25

Frost across zone 6a

Last spring frostmedian Apr 28Full range across the zone: Apr 4 to Jun 21Most of the zone (10th to 90th percentile): Apr 16 to May 10Zone median: Apr 28
First fall frostmedian Oct 17Full range across the zone: Sep 6 to Nov 12Most of the zone (10th to 90th percentile): Oct 5 to Oct 24Zone median: Oct 17

Frost-free season (median)

Figure 2. Frost dates across zone 6a, from 924 NOAA stations matched to 4,375 ZIP codes.

Planting carrots with others

Onions Tested in a study Intercropped onions reduced carrot fly (Psila rosae) attack on carrots, probably because onion volatiles disrupt host finding; onion thrips on the onions were also reduced.6 6 6 7 8 8
Marigold Tested in a study Claimed: French marigold protects carrots from carrot fly. Tested: mixing carrots with French marigold (Tagetes patula) did not reduce carrot fly.6
Lettuce Extension guidance Deep-taprooted carrots paired with shallow, wide-rooted lettuce use different soil layers, so their roots compete less.7 8 8

Sources

Colorado State University Extension, Vegetable Planting Guide (CMG GardenNotes #720), reviewed September 2024. Retrieved 2026-11-02.
NOAA National Centers for Environmental Information, U.S. Climate Normals 2020: U.S. Annual/Seasonal Climate Normals (1991-2020), 2021. Retrieved 2026-11-02.
Utah State University Extension, Suggested Vegetable Planting Dates for Utah, January 2018; revised May 2025. Retrieved 2026-11-02.
Oregon State University Extension Service, Eastern Oregon seed-starting schedule, Revised April 2025. Retrieved 2026-11-02.
Texas AgriLife Extension Service, The Texas A&M System, Texas Home Vegetable Gardening Guide (E-502), 2/09. Retrieved 2026-11-02.
Entomologia Experimentalis et Applicata 36(2):159-167 (John Wiley & Sons); abstract read via FAO AGRIS, Effect of mixed cropping on some insect pests of carrots and onions, 1984. Retrieved 2026-11-02.
Washington State University Extension, Gardening with Companion Plants (Home Garden Series), EM128E, December 2023. Retrieved 2026-11-02.
University of California Agriculture and Natural Resources (UCCE Master Gardener Program), Companion Planting Chart: Companion planting in the vegetable garden, File dated 2023-09 in URL path; no date printed. Retrieved 2026-11-02.