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Garden Help Desk: Proper watering, shade cloth and more can protect plants from summer heat

By USU Extension - Special to the Daily Herald | Jun 1, 2024
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Twenty-percent to 30% shade cloth may not look like it's providing much shade, but when afternoon sun reaches garden vegetables during summer heat, it can provide a few degrees of protection.
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Tree fruits can be "scalded" by exposure to direct sun during hot summer afternoons. Adequate fertilizer early in the year and proper pruning can provide good leaf coverage that protects tree fruits.
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Using a 3-inch layer of bark nugget mulch in shrub beds and around trees can keep the soil cooler and help trees and shrubs tolerate hot days better.
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Mulch in vegetable and flower beds can help to keep the soil cooler during hot weather. If you're using drip irrigation, the drip line or emitters should be underneath the mulch, not on top.
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There are many heat-tolerant flowering plants, like this brightly hued lantana, that will add color to the landscape while standing up to hot summer weather.

We’re used to taking steps to protect our gardens and flowerbeds from late spring or early fall frosts, but this year we may need to give our plants a different kind of protection — protection from summer heat. We normally have a few weeks of hot summer days, but this year’s summer forecast is for temperatures that may be above our norms.

There may be heat stress for some plants, and insect pests may be seen a bit earlier. High temperatures can temporarily stop photosynthesis and growth, affecting the size and quality of our harvests. Some of our favorite vegetables may have poor fruit set because high temperatures have damaged pollen, preventing pollination. Other vegetables, like tomatoes and peppers, may have fruit damage due to exposure to direct sun during the hottest part of the day. Tree fruits with direct exposure to direct sun and high temperatures may develop sunscald.

Fruits, vegetables and flowers aren’t the only plants that can be challenged by high temperatures. Lawns, trees and shrubs also need careful attention when summer temperatures are frequently above average.

There are several things we can do to reduce the heat stress our landscapes may experience this year.

If you are a container gardener, position your container gardens and potted plants where they will get a few hours of afternoon shade. Use cache pots — plants in pots tucked into slightly larger pots to protect the inner pot, soil and roots from the heat of direct afternoon sun on the containers.

Vegetable and flower gardeners have several strategies they can use this summer. For any vegetables or flowers that haven’t been planted yet, gardeners can look for varieties that are more heat tolerant. Use mulch around your vegetable and flower plants once garden soils have warmed a bit. Not only will this slow evaporation from the soil, but it will also give your plants cooler root zones.

An inch or so of plant-based compost is a good option, but lawn clippings and shredded paper will also work well. Unlike plastic mulch, none of them need to be removed at the end of the season.

Watering deeply, but not frequently, will encourage deeper rooting and more robust, efficient root systems. Adequate fertilizer during spring and early summer will promote good leaf coverage to help protect tomatoes, peppers and other fruits from afternoon sun.

Shade cloth is another tool for areas where good looks aren’t a priority. A 20% to 30% shade cloth can provide a few degrees of afternoon benefit while still providing enough sun for good growth. Suspend the shade cloth a few feet above your crop to allow room for heat to escape instead of building up under the cloth.

You’ll get the best quality for your efforts if you harvest your fruits, vegetables and cut flowers in the morning. Bring them indoors as soon as you can to keep them cool and preserve their quality.

Trees and shrubs need deep, infrequent watering in the morning. Give them a deep soak, but only once a week during the summer and less often in the fall when things begin to cool off. Use a 3-inch layer of organic mulch, such as bark nuggets, in shrub beds and around trees, too.

Even if you’ve reduced the size of your lawn, that green patch can help keep the landscape cooler. Give the lawn a deep, infrequent morning soak (about once every three to five days, depending on your soil type), mow your lawn 3 to 3.5 inches tall and use a mulching mower to help shade and mulch the soil and reduce evaporation.

One last item: Plants use transpiration (evaporation from leaves, flower and stems) to cool themselves. Do your watering for all your plants in the early morning so they’re well hydrated before having to deal with the heat of the day. This is more beneficial for your landscape than trying to do “catch-up” watering later when plants seem heat stressed.


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