Is your soil warm enough for pre-emergent yet?

55°F is when you spray, not when crabgrass germinates

One thing this tool will not tell you: that 55°F means crabgrass is germinating. It does not. 55°F is when you spray; Purdue puts germination itself at 57 to 64°F. Confusing the two is the most common way people end up a season late.

When to apply pre-emergent carries both figures with their sources, and our pre-emergent comparison covers which active to put down once the timing is right.

The depth is part of the number

Michigan State's trigger is measured at the 0 to 2 inch depth. This tool reads 6 cm — 2.4 inches — which is the closest modelled depth to the bottom of that band. It does not show the model's surface value: that figure is bare ground in full sun and behaves nothing like soil under a turf canopy, so it reads alarmingly high without telling you anything useful about your lawn.

What this tool is

Soil temperature and place lookup from Open-Meteo, licensed CC BY 4.0. Values are numerical weather model output for the coordinates given, not observations from a sensor at your address.

For the researched date rather than today's reading, pre-emergent timing by state puts every state's window in one table. The two answer the same question from opposite ends: that page has the date, this one has the temperature.

For the whole season rather than one number, the lawn care calendar builds a state-and-grass programme from the same research this tool reads its local windows from.

FAQ

Is this my actual soil temperature?

No, and the distinction matters. The number comes from a numerical weather model that estimates soil temperature for a set of coordinates. It is a good regional estimate and a poor reading of one lawn, because shade, slope, thatch depth, irrigation and hard surfaces nearby all shift real soil temperature by several degrees. Treat it as the regional trend, and use a soil thermometer for a decision you are actually spending money on.

Which depth should I be looking at?

Michigan State Extension's application trigger is soil temperature at the 0 to 2 inch depth, and this tool reads the modelled value at 6 cm — 2.4 inches — the closest depth to the bottom of that band. It deliberately does not show the model's 0 cm surface figure: that is bare ground in full sun, it can read 40 degrees above the soil under your grass, and it would look like a malfunction rather than a measurement.

Does 55°F mean crabgrass is germinating right now?

No. That is the single most common misreading of this number. Michigan State's 50 to 55°F is the recommended application temperature — the point at which you want the pre-emergent down. Purdue puts crabgrass germination itself at 57 to 64°F, with the heaviest germination around 73°F. The application figure is deliberately earlier than the biology, because a pre-emergent has to be in place before the seed germinates.

One warm day and the number crossed 55. Do I spray today?

Not on one day. The published wording is that soil temperatures consistently reach 50 to 55°F, and a single warm afternoon in February is not that. Michigan State also frames the optimum as a range in growing degree days — 250 to 500 GDD — and notes you do not have to apply on one exact day. The window is wider than the panic suggests.

Does this work outside the United States?

The temperature lookup will return a number for coordinates anywhere, but the interpretation on this page is built on US extension guidance and our own state-by-state research, and the place search is restricted to the United States. Outside the US, treat the reading as a raw number and get the timing from your own local extension service.