Growing Degree Days in Arizona

Arizona has accumulated about 4442 growing degree days (base 50°F, since January 1), averaged across 4 NOAA USCRN stations. Station totals range from 2298 to 6410 GDD. The total climbs through summer and levels off as temperatures fall.

These are base 50°F growing degree days accumulated from January 1, the turf-industry convention. Each day adds the amount its average air temperature runs above 50°F, floored at zero. Totals from a different base or start date are not interchangeable, so the model is stated explicitly wherever a number appears.

Turf managers track the running total to time temperature-driven tasks: crabgrass pre-emergent before germination, annual bluegrass seedhead suppression, plant growth regulator reapplication, and grub control. Growing degree days are a timing signal read against a model, not a fixed calendar date.

Arizona has banked 4442 GDD (base 50°F) through August 16. That is 525 GDD ahead of 2025, when Arizona had banked 3917 GDD by August 16, based on 4 stations with records for both years.

This page reads Arizona's accumulation against the published turf models, each on its own base temperature and start date: Michigan State's crabgrass pre-emergent timer (250 to 500 GDD base 32°F from February 15) and germination timer (200 to 600 GDD base 50°F), Purdue's spring broadleaf windows by formulation, Iowa State's Japanese beetle emergence range, and the professional models for annual bluegrass seedhead suppression, early-season dollar spot, and growth regulator intervals. A target range means nothing without its base and start date, so both travel with every number.