Arizona planting calendar

When to plant thyme in Arizona — sow, transplant & harvest dates

Arizona is mostly USDA zone 9a (range 4b-10b). Dates below are derived from thyme's frost tolerance and Arizona's frost window — not generic national averages.

Thyme planting timetable for Arizona

Stage	When in Arizona	Anchor
Start seeds indoors (spring crop)	late December (December 21)	8 weeks before the last frost (mid-February (low desert))
Transplant outside (spring crop)	mid-February (February 15)	0 days after the last frost (mid-February (low desert))
Spring-crop harvest	mid-May onward, before peak summer heat	85-day crop — finishes before mid-summer
Plant the fall crop	late August (August 28) — once the worst heat breaks	~99 days before the first fall frost (early December (low desert))
Fall-crop harvest	late November into early winter	85-day crop — often the more productive of the two

Dates are state-wide averages for the dominant zone. Local microclimates — elevation, urban heat, coastal moderation — can shift the window by 1-2 weeks. Use the frost-date calculator for a date tuned to your town.

Why Arizona's climate shifts the thyme dates

Arizona's long hot summer shuts down fruit set, so locals run two short crops — a spring planting and a fall planting — around a deliberate mid-summer pause, instead of one long northern-style season. Arizona ranges from snowy mountain forest to frost-free low desert. In the desert, summer heat is the binding constraint and winter is the prime growing season.

Start seeds indoors 8–10 weeks before the last spring frost; germination takes 14–21 days at 18–21 °C (65–70 °F). Harden off transplants and set out around the date of last frost — thyme is perennial in USDA zones 5–9 (RHS H5) but resents waterlogged soil far more than cold. In the first growing season allow only light harvesting so the plant can establish; full harvests from the second year onward, cutting stems back to 4–5 cm above woody growth.

Frost-risk note

A light frost in the high country around Flagstaff (zone 4b-6a) can clip an early spring planting; the bigger risk is mid-summer heat sterilising flowers.

Regional variation within Arizona

the low desert around Yuma and Phoenix (zone 10b) can start the spring crop weeks earlier and may garden almost year-round; the high country around Flagstaff (zone 4b-6a) runs a shorter, more northern-style single season.

Phoenix — USDA zone 10a
Tucson — USDA zone 9b
Flagstaff — USDA zone 6a
Yuma — USDA zone 10b
Mesa — USDA zone 10a

What else to plant in Arizona around then

Pair the spring slot with other heat-lovers (peppers, squash, beans); use the cool October–February window for greens and brassicas.

Quick-grow guide

Sun: Full sun — 6+ hours direct.
Soil temperature for germination: 18–21 °C (65–70 °F).
Spacing: 6–8 inches (15–20 cm) between plants.
Days to harvest: ~85 days from planting out.

Frequently asked questions

When is the best time to plant thyme in Arizona?

In Arizona (mostly USDA zone 9a), sow thyme indoors around late December, set the spring crop out mid-February, harvest before peak summer heat, then plant a second crop late August for an autumn harvest. Avoid mid-summer. Thyme are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

What USDA zone is Arizona?

Most of Arizona sits in USDA hardiness zone 9a, with the state spanning roughly 4b-10b from the high country around Flagstaff (zone 4b-6a) to the low desert around Yuma and Phoenix (zone 10b). The last spring frost averages mid-February (low desert) and the first fall frost early December (low desert).

Can you grow thyme in Arizona?

Yes. Arizona's dominant zone 9a supports thyme — the key is timing. Thyme are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

Does the planting date change across Arizona?

What else can I plant in Arizona around the same time?

Pair the spring slot with other heat-lovers (peppers, squash, beans); use the cool October–February window for greens and brassicas.

Source and methodology

State zone spans from the USDA Plant Hardiness Zone Map (2023); frost-date averages from NOAA Climate Data Online. Hot-state two-season timing cross-checked against the UF/IFAS Florida Gardening Calendar and the University of Arizona Cooperative Extension planting calendar. Curated by the Growli editorial team.