PlantAlong

When to plant carrots in zone 5b

Sow outdoors between Apr 17 and May 1. That is from 2 wk before to on the zone 5b's median last frost, May 11. Across most of zone 5b that date falls between Apr 7 and May 17.

Why a range: zone 5b is defined by winter lows, not frost dates. Its ZIP codes have median last frosts from Apr 21 to May 172, 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 5b's frost dates.

Last reviewed
Stations
687
ZIP codes
2,445
Photo: Markus Spiske / Pexels
These dates use the typical last frost for the whole zone. Your ZIP code gives a closer answer.
  1. Sow outdoorsColorado 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 5b. 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 17range Apr 7 – May 17

Five digits. The calendar is computed on your device.

What each source says, applied to zone 5b

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 5b's median frost dates.

Table 1. Carrots rules from every source, at zone 5b's median last frost (May 1) and first frost (Oct 11).
SourceWhatRuleZone 5b median
Colorado State1Used aboveSow outdoorsFrom 2 wk before to on the last frostApr 17 – May 1
Utah State3Sow outdoors2 weeks before last frostApr 17
Oregon State, eastern OR4Sow outdoors4 weeks before last frostApr 3
Texas A&M (E-502)5Sow outdoors4-6 weeks before last frostMar 20 – Apr 3
Texas A&M (E-502)5Plant for fall12-14 weeks before first frostJul 5 – Jul 19

Frost across zone 5b

  1. Last spring frostmedian May 1
  2. First fall frostmedian Oct 11
  • Frost-free season (median)
Figure 2. Frost dates across zone 5b, from 687 NOAA stations matched to 2,445 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.666788
  • 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.788

Sources

  1. Colorado State University Extension, Vegetable Planting Guide (CMG GardenNotes #720), reviewed September 2024. Retrieved 2026-11-02.
  2. NOAA National Centers for Environmental Information, U.S. Climate Normals 2020: U.S. Annual/Seasonal Climate Normals (1991-2020), 2021. Retrieved 2026-11-02.
  3. Utah State University Extension, Suggested Vegetable Planting Dates for Utah, January 2018; revised May 2025. Retrieved 2026-11-02.
  4. Oregon State University Extension Service, Eastern Oregon seed-starting schedule, Revised April 2025. Retrieved 2026-11-02.
  5. Texas AgriLife Extension Service, The Texas A&M System, Texas Home Vegetable Gardening Guide (E-502), 2/09. Retrieved 2026-11-02.
  6. 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.
  7. Washington State University Extension, Gardening with Companion Plants (Home Garden Series), EM128E, December 2023. Retrieved 2026-11-02.
  8. 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.