View Full Version : Soil Temperature vs. Air Temperature and Seed

01-16-2008, 06:32 PM
Generally we put down pre-em when the soil temperature is 50-55 or so. Crabgrass germinates between 55-60 when the soil temperature stays in that range for 7-10 days. When using a thermometer to check the soil temp, the probe is down a couple of inches. Weed seed lies much closer to the surface than that. If we wait for the soil temp to rise to the germination temp, then are we behind the curve???? I'm thinking that when the air temps stay around 50-55, the soil temp won't be far behind. Any thoughts on the situation.
Just thinking out loud. Roy

01-16-2008, 09:13 PM
I don't know about south carolina, but in n. indiana when temps during the day are 50-55, that means night time temps are still in the upper twenties and low thirties. Even the first 1/4 inch of soil is going to be pretty cold until maybe the afternoon.

01-17-2008, 12:34 AM
Crabgrass, chickweed, dandelions, etc generally are problems only where turf is not aggressive, and thin.

It's safe to say most people place their soil thermometers in more 'ideal' , and much " thicker " turf...

That extra grass 'canopy', in my experience, is a much bigger temperature 'curve' than the inch or so extra depth you're talking about.

01-17-2008, 06:59 AM
Begining about Mid-February a good thing to do would check air temp, surface temp, soil temp at I", soil temp at 2" and at 3" at 6:00AM and 12:00AM and 6:00PM. Do this about three days apart. Deeper temps should remain constant while the surface will show significant change. The canopy (dormant dry grass) may keep surface a bit warmer.
Anyway, I'm gonna record it and see. Nothing like a little research to see what is going on. After 7-10 days of 60 degree air temp the sand is warm IF night temp do not drop. Another factor to consider for applying pre-em at the right time.
Just thought I share some out loud thinking. I use one of those instant read meat thermometer that goes easily into soil. Roy