How to Help Your Plants Survive Summer's Heat
In the heat of the summer, there is nothing I like better than relaxing on the deck, drinking a mojito and admiring my garden. However, the long, hot days of summer can make the plants in our landscape look straggly and tired. With a little bit of care, you can revitalize them, enjoy the scenery and some of those mojitos.
The most common stress on our plants is desiccation, or drying out. The dry winds and heat may cause plants to sag and wilt. Spraying or misting the leaves with water will revive most plants. The water will cool the leaves and increase the plant’s efficiency at drawing water up from the soil. If you are going to use your garden hose, be sure to let the water run on the lawn until the water cools so that you’re not spraying hot water on already heat-stressed plants.
After giving your plants their shower, check your irrigation system. Make sure your drippers, emitters and sprinklers are not clogged, and that there are no breaks in your lines. Pay close attention to your watering regime. Most plants in your landscape will benefit from less frequent, deeper watering. During the heat of summer, deeply water your plants about twice a week. Deeper soaking encourages deep root growth and allows plants to draw water from deeper in the soil.
You also want to reduce the amount of water lost from evaporation. Many people are surprised to learn that water can be wicked up and out of the soil through evaporation. To reduce soil evaporation, cover your soil with an organic mulch, such as wood chips, compost or straw. Put down at least 3 inches of mulch, taking care to pull it back from the plant bases. The mulch will help keep the soil cool and moist, as well as suppress weed growth.
Why is it that so many weeds seem to do just fine in the scorching heat, while our landscape plants struggle? You can try hand pulling weeds that aren’t too difficult to remove or abundant. You can also cut them to the ground and try smothering them with a thick layer of mulch. As a last resort, you can spot spray difficult or aggressive weeds with an appropriate herbicide. However, it is very important to use herbicides when temperatures are low and winds are still.
Never spray an herbicide in the heat of the day or when it is windy. Herbicides will volatilize, meaning they will go directly from a liquid to gas, in the presence of heat and sunlight. When an herbicide is a gas, it is less likely to make direct contact with plants and more likely to be inhaled by you. Remember to always read and follow the label directions and wear appropriate protective clothing.
These same precautions also apply to using insecticides. Spider mites flourish in hot, dry summer weather. We also often see aphids all season long on their favorite plants. Fortunately, it is not necessary to spray insecticides to control spider mites or aphids, as both are easily controlled with water. Simply spraying infested plants with water will remove many of the insects and raise the humidity, thus altering the habitat of the insects. Spraying with water also has the added benefit of cooling off your plants. If you have herbaceous (nonwoody) perennials that aphids seem to especially love, such as milkweed and columbine, you can install a few micro-jet sprayers directed at the plants to discourage pests. Remember, insecticides are nonselective. They will kill all insects, even the beneficial ones. You want a robust population of beneficial insects in your garden for natural pest control, so use insecticides only as a last resort.
Deadheading, or removing dry, spent flowers, will instantly make your plants look better. For most flowering plants, you can cut low on the stem, or to the nearest bud. This will encourage a second bloom.
Once you’ve deadheaded, weeded, sprayed off the insects, and improved your watering regime, you may be tempted to give your plants some fertilizer. Don’t. Fertilizing in the heat of the summer can stress plants by increasing the salt content of the soil, and encouraging rapid and unsustainable growth. Besides, most woody plants (trees and shrubs) don’t even need fertilizer. With regular applications of organic mulch, most perennials don’t need fertilizer either.
What you can do during these hot summer months is notice where you have bare spots in your yard, and create a plan for filling them. For a quick fix, you can temporarily fill them with heat-tolerant annuals, such as cosmos, salvia, lobelia, or alyssum. Herbs such as basil, parsley, and borage also fill in nicely and provide tasty additions to meals. For a long-term solution, consider planting some ornamental grasses when the weather cools down a bit. Ornamental grasses are especially nice because they increase the biodiversity of your garden, typically use less water, and are interesting to look at year-round. Taller varieties can also be used to shade more heat-sensitive perennials.
Providing good cultural care, such as proper planting, pruning, mulching and watering, is the best way to help your plants survive summers hot spells. Also, choosing plants that are native, drought-tolerant or adapted to southwestern Montana will reduce maintenance and water requirements.
This is a reprint of an article I wrote when I was the commercial horticulture program coordinator for the western area of University of Nevada Cooperative Extension.
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