Arizona planting calendar

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

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

Watermelon planting timetable for Arizona

Stage	When in Arizona	Anchor
Start seeds indoors (spring crop)	mid-January (January 18)	4 weeks before the last frost (mid-February (low desert))
Transplant outside (spring crop)	early March (March 1)	14 days after the last frost (mid-February (low desert))
Spring-crop harvest	mid-May onward, before peak summer heat	80-day crop — finishes before mid-summer
Plant the fall crop	early September (September 2) — once the worst heat breaks	~94 days before the first fall frost (early December (low desert))
Fall-crop harvest	late November into early winter	80-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 watermelon 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 3–5 weeks before last frost; transplant only after all frost danger is gone and soil is consistently 65–70 °F (18–21 °C) — cold soil causes stunted growth and root rot. Days to harvest range 70–90 from transplant depending on variety (icebox types ~70 days, full-size ~85–90 days). In zones 9–11 direct sowing is practical; in zones 3–5 choose early-maturing varieties (≤80 days) to beat first fall frost.

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 — 8+ hours direct.
Soil temperature for germination: 21–35 °C (70–95 °F).
Spacing: 36–48 inches (90–120 cm) in-row; 72–96 inches (180–240 cm) between rows between plants.
Days to harvest: ~80 days from planting out.

Frequently asked questions

When is the best time to plant watermelon in Arizona?

In Arizona (mostly USDA zone 9a), sow watermelon indoors around mid-January, set the spring crop out early March, harvest before peak summer heat, then plant a second crop early September for an autumn harvest. Avoid mid-summer. Watermelon are frost-tender — a single light frost kills seedlings, so they only go outside once frost danger has fully passed and the soil is warm.

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 watermelon in Arizona?

Yes. Arizona's dominant zone 9a supports watermelon — the key is timing. Watermelon are frost-tender — a single light frost kills seedlings, so they only go outside once frost danger has fully passed and the soil is warm.

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.