How To Keep Garden Soil Cooler During Extreme Heat

Even if you enjoy every minute, gardens take a lot of work to establish and maintain. It can be disheartening to see plants in the vegetable garden and flower beds suffer during extremely hot temperatures that often coincide with periods of drought. Keeping garden soil cooler can help plants survive these conditions more easily. Let’s take a look at ways you can help garden soil beat the heat this summer.

Why Does Garden Soil Temperature Matter?

Every plant has a temperature requirement for its system to wake from dormancy, take in nutrients, and thrive. Most seeds will not germinate if the soil is too cold. However, if the soil is too hot, water evaporates too quickly, roots are unable to take in nutrients from dry soil, and organic matter begins to decompose more quickly.

Water Deeply And Correctly

Watering your garden soil the right way will help it retain more cooling moisture. Consider using drip irrigation rather than quick, daily overhead sprinkles. Short watering sessions only dampen the top layer, and the water evaporates quickly, leaving soil cracked and dry. Longer weekly or bi-weekly sessions applied directly at soil level will benefit plants and promote healthy roots that are more likely to survive extreme temperatures. The soil should be nearly saturated to a depth of at least 6 inches deep, so it will remain cooler longer.

Mulch, Mulch, Mulch

Mulch is a garden’s best friend during extreme heat. A layer of organic mulch— straw, tree bark, compost, leaves, or pinestraw—applied in early spring will offer protection throughout the growing season. It helps the soil retain moisture and prevents crusting, regulates soil temperature, suppresses weeds that steal water, and provides shade for shallow-rooted plants. The mulch should be applied in a layer that is 2 to 4 inches deep.

If you have a bare area in your garden, add mulch or a ground cover to reduce erosion risks and nutrient run-off, moderate soil temperatures, and slow the evaporation of water from your soil that can affect planted beds.

Avoid Over-Working The Soil

If you plan to till or turn the soil in your vegetable or flower garden, get it done in the early spring or wait until fall. Tilling or plowing in the summer disturbs the soil’s delicate ecosystem and exposes moist soil to rapid water loss. When planting in the summer, consider a no-dig garden to disturb the soil as little as possible.

Create Some Shade

Trees, hedges, and shrubs provide shade that affects soil temperature. If the sun patterns have changed in your garden due to tree removal or trimming, or you don’t have any shade, there are ways to add shade to keep the soil cooler and to protect plants that suffer from the punishing afternoon sun.

• Practice companion planting so that tall crops like corn will provide shade for more tender plants such as sprawling squash vines. The shade will also help prevent produce from becoming sunburned.
• Add an arbor or trellis covered with a sun-loving vine like bougainvillea or a climbing rose to protect plants that prefer cooler roots and soil temperatures.
• Construct a simple shade structure with a PVC frame and a 30% to 50% shade cloth covering to prevent sun-baked soil and dramatically lower soil temperature.

Reduce The Amount Of Hardscape

Large boulders, concrete paths, and driveways that are exposed to direct sun all day increase daytime and overnight temperatures of the soil nearby. Removing the concrete and using gravel for paths and driveways can help cool the soil. The gravel does store heat during the day, but it allows water to penetrate the soil, keeping soil temperatures lower for planted areas nearby.

Tend To The Soil Year-Round

Plan ahead for next year by protecting and enriching the soil during cooler fall and winter temperatures. Leave vegetable and annual plant roots in place until the spring. The roots leak sugars and other compounds that support microbial populations to build organic matter that helps improve the texture of soil and help keep it cooler. Plant cover crops in the fall to prevent erosion, build up organic matter, and improve soil texture to help maintain moisture when the extreme temperatures arrive.