What you need
A metal probe thermometer, either a dial soil thermometer or a digital kitchen probe. Anything with a stem long enough to reach 4 inches works. Push a screwdriver in first if the ground is hard, so the probe does not bend.
How deep
- 2 inches for weed timing. Crabgrass and most annual weeds sprout from seed in the top inch or two, so pre-emergent timing follows this depth.
- 4 inches for seeding and feeding. Grass seed and roots respond to this steadier layer.
When to read it
Soil near the surface swings through the day: coolest around sunrise, warmest in mid-afternoon. A morning reading is the conservative one and the easiest to repeat. Our pages estimate the daily average, which sits between the morning low and the afternoon high. Whatever time you choose, use the same one every day and look at the trend over three to five days rather than one number.
Where to read it
Pick a spot that represents most of the lawn: in turf, away from pavement, walls, mulch beds and downspouts. South-facing slopes and strips next to driveways warm a week or more ahead of shaded lawn, which is also where crabgrass usually shows up first. If your yard has both, read both.
Comparing with our numbers
Our city pages estimate soil temperature from the nearest long-record weather station. Tested against 190 USDA soil sensors on years the model never saw, the 2-inch estimate was off by 3.3°F on an average day, and it put the spring 55°F date within a median of 3 days. Your yard can differ by more than that, especially in shade or under irrigation. If your thermometer and our page disagree, trust your thermometer for your yard, and use the page for the trend and the forecast.
