I don’t know about you, but by the time we hit mid-August, I’ve had quite enough of the heat. And don’t imagine that the plants in your landscapes like the heat any better. Other than tropical plants, which love this time of year, most plants are as ready as we are for cooler weather.
The heat takes its toll over the summer. By this time, many plants, particularly those that do not deal with the heat well or were planted in the last year or two, may be showing stress symptoms. Heat-stressed plants are weakened, and we often see an increase in disease and insect problems at the end of the summer.
Trees and shrubs planted within the last year may be showing stress symptoms such as wilting, brown leaf edges, poor leaf color and leaf drop. These recently planted plants have not yet become established. Establishment occurs when the roots in the original root ball grow out into the surrounding soil. Until that happens — and it takes a year or two for trees and shrubs to become established — plants cannot access moisture in the soil much beyond the original root ball.
To help these plants, pay careful attention to water. We have had fairly regular rainfall this summer and no pronounced drought periods. But anytime a week passes without significant rain, it’s a good idea to water deeply and generously once a week until it rains one-half inch or more.
Also make sure beds with newly planted shrubs are mulched. Mulches help maintain even soil moisture by preventing evaporation from the surface. Mulches also help moderate soil temperatures, keeping the soil cooler than if the sunlight shines directly on it. If frequent afternoon rains keep the soil in beds soggy, pull back the mulch to allow the soil to dry.
Keep your eye out for pests such as mealybugs, aphids, leaf hoppers, scales and whiteflies. Another pest, spider mites, can also be very damaging to a wide variety of plants. A good low-toxicity spray for these pests is a light horticultural oil spray (Year Round Spray Oil, All Seasons Spray Oil, Neem Oil and others) during the early morning hours when temperatures are cooler.
Diseases will be particularly bad with frequent afternoon rain showers. Root rots are common in bedding plants and even shrubs when frequent rains keep the soil wet; they are best prevented by making sure that beds are well drained.
Cercospora leaf spot on crape myrtles is already widespread due to frequent rains over the last few weeks. This disease causes the leaves to become spotted and then turn yellow or orange and fall off. My Natchez crape myrtles are dropping lots of leaves. Although the dropping leaves may be a nuisance, there is no need to take any action. Cercospora leaf spot does not significantly hurt the trees and is not life threatening.
In August, our yards and gardens may look a little tired (after our long, hot summer gardeners look a little tired, too). Continue to do most of your work in the cooler morning and evening hours. Do be aware that gardeners are particularly prone to mosquito bites when we work in the early morning and evening hours. Don’t forget to use insect repellent to keep them from biting you if you are out at those times.
Uprooted irises with rhizomes showing.
Divide Louisiana irises
Louisiana irises should be divided and transplanted now through September. Each year, Louisiana irises grow and spread, creating more rhizomes and shoots. Eventually, the plants can become crowded, and that leads to lower vigor and poor flowering. This generally occurs three or more years after the bed is planted, depending on how close they were planted to begin with.
Unlike most plants, Louisiana irises are at their most dormant stage in late summer, making now the ideal time to divide them. To divide your irises, dig up a clump using a shovel or garden fork. Be careful not to damage the rhizomes. Break or cut off the young rhizomes — which have new green growth at their tips — from the large, old rhizome. Discard the old rhizome and replant the young rhizomes.
Before replanting, take the opportunity to improve the bed by digging a 2-inch layer of compost or other organic matter into it. Do not let the exposed roots of the irises dry out while you do this. When the bed has been reworked, plant the rhizomes horizontally with the fan of foliage facing the direction you want the plant to grow, and carefully cover all the roots. The top of the rhizome should barely show above the soil surface. Mulch the bed about two inches deep and water thoroughly.
A worker trims a tree away from utility lines.
Hurricane season precautions
August and September tend to be the most active months for hurricanes. Before a hurricane threatens, it is important for shade trees in the landscape to be carefully checked to make sure they are in good shape. Look for any large dead branches in the tree. These should be removed. In addition, branches that hang close to or touch the roof of your house may need to be pruned or removed.
Look at the overall condition of the tree. A tree that is sickly, low in vigor and shows significant signs of rotten or decayed areas in the trunk should be cut down if it poses a threat to buildings.
Local licensed arborists and tree removal services can do this work for you. Do an internet search using "Louisiana licensed arborist list" and click on the link to the list provided by the Louisiana Department of Agriculture and Forestry.
Also make plans now for how you'll pick up and store any loose objects in the landscape, such as toys, tools, hanging baskets, potted plants and garden art. These objects can become deadly projectiles when winds reach over 100 mph.