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The Cooling Powers of Mulch!


We all know that fresh mulch is like a fresh coat of paint for your garden – instant makeover! But did you know that applying a proper 3” layer of natural mulch keeps underlying soil temps more than 20 degrees cooler?!

Gill’s Landscape Designer, Kathy Hubner recently attended a webinar presented by Bartlett Tree Research Laboratories in which they shared amazing results from a mulch study in San Antonio. Soil temperatures were measured at 6″ deep (where plant roots live) on a 105 F summer day. Bare soil, 6″ down was 102 F. Soil under grass was 92 F. Soil beneath a 3″ layer of mulch was only 76 F!! Mulch for the win!

Before a Fresh Mulch Layer…

Keeping plant roots cool helps them take up water and nutrients and prevents heat stress on the plant. Cooling powers alone are a great motivation to maintain a 3″ mulch layer, but there are lots of other key benefits. Mulch helps you water: it helps retain depth moisture in the soil when you water slow and deep.

A 3″ mulch layer also helps suppress weeds. It allows good water, oxygen, and nutrient transfer, but blocks light that weed seeds need in order to sprout. And speaking of nutrients, natural hardwood mulch or pine straw mulch breaks down over time and helps build healthier soil.

After Fresh Mulch!

To achieve a 3″ layer of mulch takes about 1 bag per 12 sq. ft. Be sure you spread the mulch evenly and avoid creating the dreaded “mulch volcano” around the trunks or main stems of plants and trees. Mounding mulch up against the trunk can invite disease. Best to mulch around trees and plants then pull mulch away from the trunk to create some space.

Pro tip: As your veggies finish their growth cycles this summer, pull them up and use a nice layer of pine straw mulch over your garden beds to keep weeds down and help keep your soil alive and ready for the next season.


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