What Grows in San Juan County, Colorado

San Juan County sits in USDA hardiness zone 4b, per the USDA Plant Hardiness Zone Map 2023. Zones reflect average annual extreme minimum temperatures from 1991–2020 weather data.

Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Apr 25; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 23 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 2 — long-season crops need about 90 days of runway, quick greens only 30. Even here the calendar’s edges hold value: thirty-day greens late in the window, then garlic and a rested bed for spring.

The last hard freeze (28°F) in San Juan County typically lands around May 23, per NOAA 1991–2020 climate normals — an earlier marker than the light-frost dates many planting charts quote. That marks the hard freeze, not the last light frost — light frosts can still bite for a few more weeks, so tender transplants usually wait another 2–3 weeks.

Measured between 28°F hard freezes, San Juan County sees about 132 frost-free days — roughly May 23 through Oct 2, per NOAA 1991–2020 climate normals. Tender crops get a somewhat shorter practical window, since lighter frosts reach a few weeks past the hard-freeze dates on both ends.

San Juan County's zone 4b supports a wide range — strong performers include Colorado Blue Spruce, Tomato, Penstemon, Apple, and Squash. What actually takes on any one site comes down to its soil, sun, and drainage, and we score each plant against the real conditions at your address.

Officially, San Juan County sits in USDA zone 4b (USDA PHZM 2023) — but a zone is a 30-year average of winter's coldest night across an area, and it can't see any one yard. A south-facing slope, a tree line, or a low frost pocket can shift a single site by half a zone either way, which is why neighboring gardeners often quote different numbers. We read the conditions at your exact address — soil, sun, slope, and frost — and score 1,112 plants against what's actually there.

The federal record around San Juan County runs heavier than most — 558 documented sites — so test the soil before planting food in the ground, and raised beds with clean imported soil grow well in the meantime. Even here, proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what's recorded and where.

With about 132 frost-free days between hard freezes, San Juan County rewards the classic extension moves: floating row cover buys roughly two to four extra weeks at each shoulder, cold frames and low tunnels more, and quick-maturing varieties make the arithmetic work. Starting transplants indoors ahead of the May 23 hard-freeze normal stretches the season without touching the calendar.