When to plant carrots in zone 9a

Sow outdoors between Feb 17 and Mar 2. That is from 2 wk before to on the zone 9a's median last frost, Mar 21. Across most of zone 9a that date falls between Feb 2 and Mar 18.

Why a range: zone 9a is defined by winter lows, not frost dates. Its ZIP codes have median last frosts from Feb 16 to Mar 182, 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 9a's frost dates.

Last reviewed: 2026-11-02
Stations: 432
ZIP codes: 1,671

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: Feb 2 to Mar 18Sow outdoors at the zone median: Feb 17 to Mar 2 (Colorado State)
Plant for fallTexas A&M (E-502)Plant for fall across most of the zone: Aug 10 to Sep 16Plant for fall at the zone median: Aug 20 to Sep 3 (Texas A&M (E-502))

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 9a. 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: Feb 17range Feb 2 – Mar 18
Fall planting: Aug 2012-14 weeks before first frost

What each source says, applied to zone 9a

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 9a's median frost dates.

Table 1. Carrots rules from every source, at zone 9a's median last frost (Mar 2) and first frost (Nov 26).
Source	What	Rule	Zone 9a median
Colorado State1Used above	Sow outdoors	From 2 wk before to on the last frost	Feb 17 – Mar 2
Utah State3	Sow outdoors	2 weeks before last frost	Feb 17
Oregon State, eastern OR4	Sow outdoors	4 weeks before last frost	Feb 3
Texas A&M (E-502)5	Sow outdoors	4-6 weeks before last frost	Jan 20 – Feb 3
Texas A&M (E-502)5Used above	Plant for fall	12-14 weeks before first frost	Aug 20 – Sep 3

Frost across zone 9a

Last spring frostmedian Mar 2Full range across the zone: Jan 6 to Jun 3Most of the zone (10th to 90th percentile): Feb 16 to Mar 18Zone median: Mar 2
First fall frostmedian Nov 26Full range across the zone: Sep 14 to Feb 1Most of the zone (10th to 90th percentile): Nov 16 to Dec 9Zone median: Nov 26

Frost-free season (median)

Figure 2. Frost dates across zone 9a, from 432 NOAA stations matched to 1,671 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.