Counties with the Longest Growing Seasons

A long growing season means more time for grass to establish, more opportunities for overseeding, and a wider window for lawn recovery. For homeowners and landscapers, counties with 300+ frost-free days offer significant advantages over regions where winter shuts down plant growth for months.

Using NOAA climate normals and USDA hardiness zone data, we identified the 25 US counties with the longest growing seasons — places where the last spring frost arrives early and the first fall frost holds off until late in the year.

Counties with the Longest Growing Seasons

Imperial County, CA leads the nation with 352 frost-free days per year. These counties stretch from South Florida to the desert Southwest and coastal California.

What This Means for Your Lawn

Counties with extended growing seasons can support warm-season grasses like Bermuda and Zoysia that go dormant in cooler climates. Homeowners in these counties also have more flexibility with seeding dates and can recover from lawn damage faster due to the longer active growing period.

Methodology

Growing season length is calculated as the number of days between the last spring frost (32°F) and the first fall frost (32°F), based on NOAA 1991-2020 climate normals. Counties missing growing season data are excluded.