Frost Dates & Planting Calendar for Flagstaff, AZ

The average first fall frost in Flagstaff, AZ is September 28, and the average last spring frost is June 4, giving a growing season of about 115 days.

Plan your garden around Flagstaff, AZ's typical frost-free growing season, using NOAA climate normals and a 42-crop planting calendar built for this location.

Last Spring Frost

June 4

Safe Jun 19 Typical Jun 4 Risky May 21

First Fall Frost

September 28

Safe Sep 16 Typical Sep 28 Risky Oct 9

Growing Season

115 days

Typical last frost to typical first frost.

USDA Hardiness Zone

Zone 6a

A classic four-season climate with cold winters and a solid summer growing season.

Data: NOAA station FLAGSTAFF PULLIAM AP, AZ US, 6.1 km away.

— days until the typical last spring frost

How Flagstaff Compares

Flagstaff's typical last spring frost (Jun 4) comes later than in 99% of the 69 Arizona cities we track.
Its 115-day growing season is 183 days shorter than the Arizona median of 298 days.
July is the warmest month (average high 82°F) and December the coldest (average low 17°F).

Monthly Temperatures

Avg. high Avg. temp Avg. low

Planting Calendar

Vegetables
Crop	Start indoors	Direct sow	Transplant	Fall planting	Maturity	Notes
Tomato	Apr 9 – Apr 23	—	Jun 11 – Jun 18	—	60–85 days	Start indoors 6-8 weeks before last frost; transplant out 1-2 weeks after last frost once soil has warmed.
Pepper	Mar 26 – Apr 9	—	Jun 11 – Jun 25	—	60–90 days	Slow to germinate; start indoors 8-10 weeks before last frost. Transplant only once nights stay above 55F, 1-3 weeks after last frost.
Eggplant	Mar 26 – Apr 9	—	Jun 18 – Jun 25	—	65–85 days	Warm-season crop, similar timing to pepper; needs consistently warm soil (65F+) to transplant.
Cucumber	May 7 – May 14	Jun 11 – Jun 18	Jun 11 – Jun 18	—	50–65 days	Can be started indoors 3-4 weeks before transplanting, or direct-sown 1-2 weeks after last frost once soil is warm.
Zucchini	May 14 – May 21	Jun 11 – Jun 25	Jun 11 – Jun 18	—	45–55 days	Fast-growing squash; direct sow 1-3 weeks after last frost, or start indoors 2-3 weeks early for a head start.
Winter Squash	May 7 – May 14	Jun 11 – Jun 25	Jun 11 – Jun 18	—	80–110 days	Long season; direct sow after soil warms, or start indoors 3-4 weeks before last frost in short-season climates.
Pumpkin	—	Jun 11 – Jun 25	—	—	90–120 days	Direct sow 1-3 weeks after last frost; back-time from your first fall frost so the 90-120 day maturity window lands before it.
Watermelon	May 7 – May 14	—	Jun 18 – Jun 25	—	70–90 days	Needs warm soil (65F+); start indoors 3-4 weeks before last frost, transplant 2-3 weeks after last frost.
Cantaloupe	May 7 – May 14	—	Jun 18 – Jun 25	—	70–90 days	Same warm-soil requirements as watermelon; avoid disturbing roots when transplanting.
Corn	—	Jun 4 – Jun 18	—	—	60–100 days	Direct sow at last frost to 2 weeks after, once soil reaches 60F; does not transplant well. Succession sow every 2 weeks.
Green Bean	—	Jun 4 – Jun 18	—	—	50–65 days	Direct sow at last frost to 2 weeks after, once soil has warmed; frost-tender, do not rush.
Pea	—	Apr 23 – May 7	—	—	55–70 days	Cold-hardy; direct sow 4-6 weeks before last frost as soon as soil can be worked.
Lettuce	—	May 7 – May 21	—	Aug 3 – Aug 17	45–60 days	Cold-hardy; direct sow 2-4 weeks before last frost. Also transplantable from indoor starts.
Spinach	—	Apr 23 – May 7	—	Aug 3 – Aug 17	40–50 days	Very cold-hardy; direct sow 4-6 weeks before last frost as soon as soil can be worked.
Kale	—	May 7 – May 21	—	Jul 20 – Aug 3	50–65 days	Cold-hardy; direct sow 2-4 weeks before last frost or start indoors for earlier transplants.
Arugula	—	May 7 – May 21	—	Aug 17 – Aug 24	30–40 days	Fast-growing, cold-tolerant green; direct sow 2-4 weeks before last frost, succession sow every 2-3 weeks.
Swiss Chard	—	May 14 – May 28	—	—	50–60 days	Fairly cold-hardy; direct sow 1-3 weeks before last frost. Tolerates light frost in fall too.
Broccoli	Apr 16 – Apr 30	—	May 14 – May 21	Jul 27 – Aug 3	55–80 days	Start indoors 5-7 weeks before last frost; transplant out 2-3 weeks before last frost (hardens off to light frost).
Cauliflower	Apr 16 – Apr 30	—	May 21 – May 28	Jul 20 – Jul 27	55–85 days	Fussier than broccoli about temperature swings; start indoors 5-7 weeks before last frost, transplant 1-2 weeks before last frost.
Cabbage	Apr 16 – Apr 30	—	May 7 – May 21	Jul 20 – Aug 3	60–100 days	Cold-hardy; start indoors 5-7 weeks before last frost, transplant 2-4 weeks before last frost.
Brussels Sprouts	Apr 16 – Apr 30	—	May 14 – May 28	—	90–110 days	Long-season crop best timed to mature after a light fall frost for sweetest flavor; start indoors 5-7 weeks before last frost.
Carrot	—	May 7 – May 21	—	Jul 6 – Jul 20	60–80 days	Direct sow only (does not transplant); sow 2-4 weeks before last frost, as soon as soil can be worked.
Beet	—	May 7 – May 21	—	Jul 20 – Aug 3	50–65 days	Direct sow 2-4 weeks before last frost; tolerates light frost.
Radish	—	Apr 30 – May 14	—	Aug 17 – Aug 31	22–30 days	Very fast and cold-hardy; direct sow 3-5 weeks before last frost, as soon as soil can be worked.
Turnip	—	May 7 – May 21	—	Jul 20 – Aug 3	40–60 days	Cold-hardy; direct sow 2-4 weeks before last frost.
Onion	Mar 26 – Apr 9	—	May 7 – May 21	—	90–120 days	Start seeds indoors 8-10 weeks before last frost (or use sets/transplants); set out 2-4 weeks before last frost, very cold-tolerant as seedlings.
Garlic	—	—	—	Aug 31 – Sep 14	240–270 days	Fall-planted crop only; not planted in spring in most climates.
Potato	—	May 7 – May 21	—	—	70–120 days	Plant seed potatoes 2-4 weeks before last frost, as soon as soil can be worked and is above 45F; light frost on emerging foliage is usually tolerated.
Sweet Potato	—	—	Jun 18 – Jul 2	—	90–120 days	Set out slips 2-4 weeks after last frost once soil is thoroughly warm (65F+); very frost/cold sensitive.
Asparagus	—	—	May 7 – May 21	—	730–1095 days	Perennial; plant crowns 2-4 weeks before last frost as soon as soil can be worked. Takes 2-3 years to full production.

Herbs
Crop	Start indoors	Direct sow	Transplant	Fall planting	Maturity	Notes
Basil	Apr 23 – Apr 30	—	Jun 11 – Jun 18	—	50–70 days	Very frost/cold sensitive; start indoors 5-6 weeks before last frost, transplant only after all danger of frost (1-2 weeks after) and nights stay warm.
Cilantro	—	May 14 – May 28	—	Aug 3 – Aug 17	45–70 days	Cool-season, bolts in heat; direct sow 1-3 weeks before last frost, succession sow through spring.
Parsley	Apr 9 – Apr 23	—	May 21 – May 28	—	70–90 days	Slow to germinate; start indoors 6-8 weeks before last frost, transplant 1-2 weeks before last frost (biennial, cold-tolerant).
Dill	—	May 14 – May 28	—	—	40–60 days	Taprooted, does not transplant well; direct sow 1-3 weeks before last frost, succession sow through summer.
Oregano	Apr 9 – Apr 23	—	Jun 4 – Jun 11	—	80–90 days	Perennial herb; start indoors 6-8 weeks before last frost, transplant around/just after last frost date.
Thyme	Apr 9 – Apr 23	—	Jun 4 – Jun 11	—	85–95 days	Perennial herb, slow from seed; start indoors 6-8 weeks before last frost, transplant around/after last frost.

Flowers
Crop	Start indoors	Direct sow	Transplant	Fall planting	Maturity	Notes
Sunflower	—	Jun 11 – Jun 25	—	—	70–100 days	Direct sow 1-3 weeks after last frost once soil has warmed; taprooted, resents transplanting.
Zinnia	May 7 – May 14	Jun 11 – Jun 25	Jun 11 – Jun 18	—	60–70 days	Frost-tender; direct sow 1-3 weeks after last frost, or start indoors 3-4 weeks early for earlier blooms.
Marigold	Apr 23 – May 7	—	Jun 11 – Jun 18	—	45–60 days	Frost-tender; start indoors 4-6 weeks before last frost, transplant after all frost danger has passed.
Cosmos	May 7 – May 14	Jun 11 – Jun 25	Jun 11 – Jun 18	—	60–90 days	Easy from direct seed 1-3 weeks after last frost; can also start indoors 3-4 weeks early.
Nasturtium	—	Jun 11 – Jun 25	—	—	50–65 days	Frost-tender, resents root disturbance; direct sow 1-3 weeks after last frost once soil has warmed.
Dahlia	—	—	Jun 11 – Jun 25	—	90–120 days	Plant tubers 1-3 weeks after last frost once soil is warm (60F+); very frost-sensitive.

Date ranges are estimates based on university extension guidelines and this city's NOAA frost normals — not a guarantee. Scroll to see all columns on narrow screens.

Frequently Asked Questions

When is the last frost in Flagstaff, AZ?

Based on 1991–2020 NOAA climate normals for the FLAGSTAFF PULLIAM AP, AZ US station, the last spring frost in Flagstaff typically falls around June 4. A cautious gardener might wait until June 19 (only a 10% chance of a later frost), while May 21 marks an earlier, higher-risk planting date.

When is the first frost in Flagstaff, AZ in fall?

The first fall frost in Flagstaff typically arrives around September 28. To stay safe, assume frost could start as early as September 16; in milder years it can hold off until October 9.

How long is the growing season in Flagstaff, AZ?

Flagstaff's average frost-free growing season is about 115 days, running from the typical last spring frost (June 4) to the typical first fall frost (September 28).

What USDA hardiness zone is Flagstaff, AZ in?

Flagstaff, AZ is in USDA plant hardiness zone 6a, per the USDA's 2023 Plant Hardiness Zone Map. A classic four-season climate with cold winters and a solid summer growing season.