When to plant carrots in zone 5a

Sow outdoors between Apr 19 and May 3. That is from 2 wk before to on the zone 5a's median last frost, May 31. Across most of zone 5a that date falls between Apr 12 and May 20.

Why a range: zone 5a is defined by winter lows, not frost dates. Its ZIP codes have median last frosts from Apr 26 to May 202, 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 5a's frost dates.

Last reviewed: 2026-11-02
Stations: 655
ZIP codes: 2,089

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 12 to May 20Sow outdoors at the zone median: Apr 19 to May 3 (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 5a. 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 19range Apr 12 – May 20

What each source says, applied to zone 5a

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 5a's median frost dates.

Table 1. Carrots rules from every source, at zone 5a's median last frost (May 3) and first frost (Oct 5).
Source	What	Rule	Zone 5a median
Colorado State1Used above	Sow outdoors	From 2 wk before to on the last frost	Apr 19 – May 3
Utah State3	Sow outdoors	2 weeks before last frost	Apr 19
Oregon State, eastern OR4	Sow outdoors	4 weeks before last frost	Apr 5
Texas A&M (E-502)5	Sow outdoors	4-6 weeks before last frost	Mar 22 – Apr 5
Texas A&M (E-502)5	Plant for fall	12-14 weeks before first frost	Jun 29 – Jul 13

Frost across zone 5a

Last spring frostmedian May 3Full range across the zone: Apr 13 to Jun 20Most of the zone (10th to 90th percentile): Apr 26 to May 20Zone median: May 3
First fall frostmedian Oct 5Full range across the zone: Sep 1 to Oct 28Most of the zone (10th to 90th percentile): Sep 26 to Oct 13Zone median: Oct 5

Frost-free season (median)

Figure 2. Frost dates across zone 5a, from 655 NOAA stations matched to 2,089 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.