Now, in the heat of midsummer, is a good time to see which plants are well-adapted to your landscape and which may not make it.

“Other than tropical plants, which we all know have problems with freezing temperatures, it is often the late-summer heat rather than the cold of winter that takes its toll here,” says LSU AgCenter horticulturist Dan Gill.

If daytime highs in the 90s weren’t bad enough, the nighttime temperatures in the mid- to upper 70s also give plants a particularly hard time.

When night temperatures stay very warm, a plant’s metabolic rate tends to stay high, burning energy and using up food it has created. Tropical plants are well-adapted to this situation, and for them it’s not a problem.

“But plants from cooler climates rely on the cooler nights,” Gill says. “When nights stay warm, these plants become weak because they use up their food too quickly.”

Add high humidity and frequent rain showers, and you have the ideal conditions for weakened, stressed-out plants to be attacked by a variety of insects and diseases — particularly crown and root rots that are so often fatal, Gill says.

“These intense environmental and pest pressures mean that only those plants that are well-adapted to our summer conditions stand a good chance of surviving and thriving here,” he says.

August is a good time to walk around the landscape with a critical eye to how things are going. Even tried-and-true plants that are reliable here may not look their best this time of the year, so don’t be too critical. In particular, Gill says, look at any new or unusual plants you’re trying out.

And keep an eye out for changing shade patterns. The amount of sunlight on any spot can be different where older trees and shrubs have been removed or newer plants have grown taller and fuller.

Many attractive and useful plants that are considered reliable and even easy to grow in other parts of the country will not thrive here. When we choose hardy trees, shrubs, ground covers, lawn grasses and perennials for our landscapes, we must primarily keep in mind the temperatures they will be subjected to during our summers.

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