Soil Temperature in Guayama, PR

For warm-season grasses, yes. The 2-inch soil temperature near Guayama, PR is currently 87.8°F, measured in the ground at the Fortuna station (USDA SCAN #2122), 28 mi W, read 3 days ago (Sep 30, 2026). That is at or above the 65°F threshold where Bermuda and zoysia establish, and above the 50–65°F cool-season band, so hold cool-season seeding until soil cools back through 65°F.

The soil at 2 inches near Guayama, PR is at 21% volumetric water content, around the 53rd percentile of the Fortuna station's own history for this time of year, so the ground is about normal for this date. This is a direct ground measurement from 326 active USDA and NOAA in-ground monitoring stations, not a forecast or a model.

Soil temperature outside the germination band is the most common cause. The 2-inch soil temperature near Guayama, PR is currently 87.8°F, measured in the ground at the Fortuna station (USDA SCAN #2122), 28 mi W, read 3 days ago (Sep 30, 2026). Cool-season seed germinates at 50–65°F and warm-season seed at 65°F or higher; outside those bands seed sits dormant rather than sprouting. If the temperature is right, the usual culprits are seed buried too deep, topsoil that dried out during the sprout window, or a pre-emergent herbicide applied the same season, which blocks grass seed the same way it blocks weeds.

Cool-season grasses like fescue and bluegrass germinate best when soil at 2 inches stays between 50–65°F for several consecutive days. Warm-season grasses like Bermuda and Zoysia need soil temperatures of 65°F or higher before seeding. If you are seeding, a high-phosphorus starter fertilizer goes down in the same window; regular established-lawn fertilizer follows different timing.

Apply pre-emergent herbicide, the product sold at retail as crabgrass preventer, when soil at 2 inches reaches 55°F for several consecutive days. This is the threshold where crabgrass and other summer annual weeds begin germinating, and applying after that point reduces effectiveness significantly. Weed-and-feed products that include a pre-emergent follow the same window. The pre-emergent timing page for Guayama tracks this threshold against the current reading.

Guayama, PR is in USDA hardiness zone 13a, mild enough that warm-season grasses like Bermuda, zoysia, and St. Augustine come through winter reliably; they go tan and dormant rather than dying. Cool-season grasses survive winter here easily but struggle through the hot summer instead.

Use 2 inches for germination decisions, since that is where seeds sit. Use the 4 inch soil temperature for established lawn and garden timing: it reads the root zone, changes more slowly than the surface, and is the depth most fertilizer, aeration, and disease guidance references. The 8 inch reading shows deeper root-zone trend. The 20 and 40 inch readings track deep soil and frost depth where federal stations report them.

Soil changes temperature much more slowly than air due to thermal mass. A warm afternoon does not mean the ground is warm. Soil temperature lags air temperature by days or weeks, making it a more reliable indicator of when biological processes like germination actually begin.

It is a direct ground measurement. The 2-inch soil temperature near Guayama, PR is currently 87.8°F, measured in the ground at the Fortuna station (USDA SCAN #2122), 28 mi W, read 3 days ago (Sep 30, 2026). Soil Temps reads from 326 active USDA and NOAA in-ground monitoring stations, which report daily at depths from 2 to 40 inches.