Seed Starting Calendar for Arizona

University of Arizona Cooperative Extension plants Arizona by region and month (see the months below), and transplants are sown 4 to 10 weeks ahead of the month they go out. Counted from the frost instead, Tucson's median last frost of February 5 puts spring 2027 tomato seeds at Dec 18 to Jan 1 and peppers at Dec 11 to Dec 25.

It depends on the station. The earliest median last spring freeze in Arizona is January 4 at Bullhead City; the latest is June 23 at Flagstaff 4 SW. A median is a coin flip: at Tucson the last 32°F freeze comes after February 5 in half of years, and has passed by March 2 in 9 of 10 years (NOAA 1991 to 2020 normals).

UNH Extension sets tomatoes out 1 to 2 weeks after the last frost, which at Tucson is Feb 12 to Feb 19 in 2027. Tomatoes are frost tender, so the date to watch is March 2, when 9 of 10 springs at Tucson have had their last 32°F night. Hardening off starts two weeks before setting out (Jan 29 to Feb 12).

University of Arizona Cooperative Extension publishes planting months by region (Low desert). For Low desert, tomatoes go in during February, March, July and August. Seeds for transplants go in 4 to 10 weeks ahead of those months, depending on the crop.

University of Arizona Cooperative Extension's Vegetable Planting Calendar for Maricopa County puts it this way: "In the low desert regions of the southwest, including Maricopa County, most any type of vegetables and fruits can be grown successfully when appropriate varieties are selected and planted at the right time." The guide is linked below with the date it was read (September 21, 2026).

UNH Extension gives 8 to 10 weeks from seed to transplant for both, and sets peppers out 2 weeks after the last frost and eggplant 2 to 3 weeks after, so the sowing date is 6 to 8 weeks before the median last frost. At Tucson that is Dec 11 to Dec 25 for peppers.

About two weeks. University of Missouri Extension: "Hardening should be started about two weeks before planting in the garden." University of Minnesota Extension adds that seedlings should go out on a cloudy day or in the late afternoon.

Phoenix passes its median last frost around Jan 5 and Tucson around Feb 5, while Flagstaff on the Colorado Plateau waits until about Jun 4; the low desert follows a planting calendar more than a frost date. Each station carries its own dates: Phoenix Jan 5 and Flagstaff Jun 4 at the median.