June 6, 2023
by Cara Bergschneider
The dog days of summer is when temperatures rise and soaking rains become less dependable. If you grow vegetables, one of the best ways to prepare is to apply a natural mulch to your crops. Mulching can improve plant health by reducing heat stress, improving water efficiency and minimizing weed pressure.
The ideal temperature for most summer vegetables is between 59 and 86 degrees F. As temperatures creep past 90 degrees for multiple days, plant growth slows. For example, curled tomato leaves mean plants are reducing surface area to conserve water. Other effects of sustained heat stress include blossom drop and increased susceptibility to disease. Mulching buffers heat stress by reducing soil temperature.
Temperatures in the upper few inches of the soil can fluctuate up to 35 degrees throughout a 24-hour period and reach highs of 115 degrees. A covered soil undergoing the same conditions will fluctuate by less than 10 degrees and stay below 86 degrees — the ideal growing temperature of summer vegetables.
Cooling effects of mulch also benefit micro- and macrobiology. These soil organisms convert nutrients into a form that plants can use, recycling plant residues into organic matter and reducing plant disease. Mulch provides a stable, comfortable soil environment for these organisms.
To see for yourself, pull back a layer of mulch on the hottest day of summer. You will find earthworms, beetles and centipedes actively moving underneath the mulch. They are consuming mulch and converting it into soil organic matter. You will not find a single earthworm, beetle or centipede on the surface of bare soil on that same scalding day.
Mulch is also good for your pocketbook. Mulching provides a barrier between the air and soil, reducing evaporation and increasing soil moisture. Less watering is needed, saving time and money.
Mulching can also greatly reduce weed pressure by providing a light barrier and reducing weed seed germination. Weeding in vegetable production is labor intensive. Pulling weeds from a mulched area is also easier and more likely to result in the roots being attached to the weed you’ve just pulled.
The type of mulch will depend upon availability, cost and crop to be mulched. The most commonly applied natural mulches are straw, leaf mold, compost, alfalfa hay and grass clippings. No matter what type of mulch you apply, a few rules of thumb hold across the board.
When using mulch, follow these simple rules:
Apply mulch correctly. Always apply mulch to a well-weeded, well-watered soil. Leave a few inches of mulch-free area around stems of plants to prevent disease and rot due to increased moisture.
Know mulch condition. Never apply mulch that has been recently treated with a herbicide or pesticide.
Know mulch source. Determine if weed seeds will be an issue. For some mulch material such as straw, germination of a small amount of wheat can be easily dealt with. Germination of yard grass from weedy grass clippings is a no-no.
Test first. If mulching is new to you, try a test area where you compare the same crop with and without mulch. Observe benefits, discover potential challenges, and see if mulching is a good fit for you.
Bergschneider is the state urban and small-scale conservationist with the Natural Resources Conservation Service in Indiana. She writes on behalf of the Indiana Conservation Partnership.
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