I use mulch whenever and wherever I can. In times past, I made some rough measurements with a thermometer and measured 12 to 15 degrees difference with only a small amount of mulch. I have read that many writers have seen a 25 to 30 degree difference. So lately in this hot and dry summer we have been having, I decided to take some serious measurements. I started making temperature measurements and found some interesting results out here in what is left of my garden. I have all my tomatoes mulched with four inches of ground up chips. These were chips from commercial tree shredders that I then ran through my chipper/shredder for smaller size chips.
I am pleased to tell you that I have matched the 25 - 30 degree difference in soil temperature and surpassed it! I made measurements in the top one or two inches of unmulched (bare) soil (dark charcoal color clay) and there was a reading of 127 degrees! I made this with three different thermometers (no wonder everything is dying). At this same time I was reading outside air temperature on our front porch (in the shade) of 103 degrees. In the root zone of the tomatoes and under the mulch, the soil temperature read from sunrise to sunset, 85 degrees, with no more than a 1 or 2 degree change. The soil under the mulch was moist (not damp, but moist!) and I could push the thermometer down into the soil at least 8 inches. I certainly could not do that in the soil that was not mulched. I had another thermometer reading the top of the soil but under the mulch. It started out cooler at 80 degrees (at sunrise) and went up to 86 degrees in the peak of the heat, which is still an acceptable temperature.
It is quite obvious this mulch is working as an insulator against the heat and helping retain some moisture in the root zones of these plants. The plants have good color and are blooming. I feel confident that when this heat lets up they will again start producing on into the fall. The lesson here is that mulching does make a difference! Take heart in this heat and begin mulching if you're not already doing so!
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Copyright - © 1999, Mary J. Tynes. Note that the copyright for the article content above belongs to Leon Brandon.