Lawn care calendar for Arizona: when to fertilize and seed

The source guide covers the low elevation desert around Phoenix, Tucson, Casa Grande and Yuma; northern Arizona lawns run on a cool-season calendar not covered here.

Which grasses grow where in Arizona

In the low desert, bermudagrass is the best-adapted lawn grass for heat and water use. Common bermudagrass can be seeded or planted as sod, plugs or sprigs. Hybrid bermudagrasses are sterile, so they have to be planted vegetatively. Both grow hard in summer and go dormant in winter, and several frosty nights in November or December turn them blonde.

Zoysiagrass and St. Augustinegrass also go dormant in winter, but the University of Arizona says they generally are not suited to overseeding. The ryegrasses (perennial, annual and the intermediate hybrid) are the usual winter lawn.

Frost dates from NOAA

Dates are the NOAA 1991-2020 normals for the last spring and first fall 32 F freeze at 50% probability. Tucson International Airport averages February 5 and December 9, about 307 days apart by our count. Flagstaff Pulliam Airport averages June 4 and September 28, about 116 days apart.

Phoenix Sky Harbor lists January 5 and January 3, two days apart in the same cold week. There is no frost-free season to count in Phoenix. The University of Arizona ties winter color loss to several frosty nights in November or December instead.

Spring

Non-overseeded bermudagrass starts greening in February when the air warms, but soil is not ready. When soil temperature is consistently 60 F, usually in April, growth picks up and light fertilizing and watering can begin. Hot, dry May and June weather starts the strongest growth.

On an overseeded lawn, the spring job is to hand the grass back to the bermudagrass. Lower the mowing height by 35 percent, mow more often, apply 0.25 pound of nitrogen weekly, keep watering, and once 80 percent of the lawn is bermudagrass, verticut lightly and fertilize at 0.25 to 0.5 pound with a week of drier soil to stress the ryegrass.

Summer

Summer is the time to plant a new bermudagrass lawn. Seed needs about a month and multiple waterings a day; sod gives a usable lawn in a week; sprigs fall in between. A new lawn should not be overseeded its first winter. After that, mow at least weekly, fertilize with half a pound of nitrogen per 1,000 square feet each month, and water deep every three days instead of daily. Use a higher-phosphate fertilizer the month you seed or sod.

Aerify or dethatch in summer when the grass is actively growing. Bermudagrass needs about 100 days of active growth to build roots and rhizomes before it can be overseeded.

Fall

October is the ideal overseeding month, when daytime highs are 80 to 85 F and nights are near 55 F. Seeding too early favors the bermudagrass, and too late risks frost on the seedlings. In the weeks before: stop nitrogen on the bermudagrass 30 days ahead, raise the mowing height 30 to 40 percent and cut irrigation 30 percent two weeks ahead, then mow back down and lower the cut another 25 to 30 percent just before seeding, and leave the clippings.

On the day, spread 12 to 15 pounds of ryegrass per 1,000 square feet in two directions and rake it in. Water three to four times a day for 7 to 10 days, then taper to about weekly, and fertilize two weeks after emergence with 16-20-0 at 5 pounds per 1,000 square feet, watering it in. First mowing is when ryegrass reaches 2.75 to 3 inches.

Winter

An overseeded lawn needs far less water than the bermudagrass did in summer, with amounts driven by soil type, temperature and rain. The university points to AZMET, the Arizona weather network, for a daily watering guide.

A dormant lawn that was not overseeded generally needs no extra water, unless winter rains are missing, in which case run the system about once a month from December through February. The lawn fertilizer calculator on this site is handy for turning the 0.5 pound monthly target into pounds of a particular bag.