By William H. Johnson
August is a month when gardeners should think about two important aspects of landscape maintenance—fertilizing and pruning.
August is the last month in the summer growing season to fertilize hardy shrubs and ground covers in the landscape. Now is also the time to finish up pruning many shrubs, cut back overgrown tropicals and trim some bedding plants. But it’s also time to stop pruning spring-flowering trees and shrubs.
You can use general-purpose granular fertilizers for most fertilizing jobs in the landscape. These fertilizers are relatively inexpensive and easy to use. If you feel you need to fertilize your shrubs or ground covers to encourage one last burst of growth, it’s important to do so now.
This is because as we move into the winter, it’s important that hardy plants in the landscape slow their growth and prepare for the coming winter season. Late fertilizer applications, especially with nitrogen, can increase the possibility of cold damage, even to plants that would normally be hardy. This is especially true for the Texas Upper Gulf Coast growing region because fall temperatures are generally warm to mild and don’t give plants a strong signal to transition to a dormant state.
For lawns, an application of a nitrogen-only fertilizer granular fertilizer (such as 21-0-0) should be applied evenly to dry, freshly mowed turf and immediately watered in. Pay careful attention to the rate of application and spread the fertilizer evenly. This is difficult to do by hand, so use a fertilizer spreader to ensure even coverage.
Shrubs and ground covers may be fertilized by sprinkling fertilizer over the entire bed where they are growing. You may also apply fertilizer by sprinkling it around each plant. The size of the shrubs is a factor in determining the amount of fertilizer used. Rates are generally higher for larger shrubs, but check package recommendations for specific amounts.
I’m not advising that every gardener should go out and fertilize plants in your landscape now. Most landscape plants don’t need to be fertilized at this time. Spring fertilizer applications are more important. If your lawn, shrubs and ground covers look healthy and have grown well this summer, there should be little indication that fertilizer is needed.
If, on the other hand, you have some plantings you have been meaning to fertilize or you feel would benefit from fertilization to boost their vigor, now is the time to do it and not later in the summer growing season.
Pruning is another topic that gardeners need to focus on at this time. Fall-, winter- and spring-flowering trees and shrubs that bloom from November through April have already set their flower buds for next year. Examples of such plants include camellias, azaleas, Indian hawthorns, and Oriental magnolias as well as summer-flowering gardenias and hydrangeas. Extensively pruning or cutting back these plants from now on will generally diminish or eliminate their flower display in the spring. It’s all right to selectively remove specific shoots or branches to shape these plants without affecting the flowering of the remaining growth. Just don’t get carried away.
Hedges, such as ligustrum, boxwood, photinia and viburnum, should be pruned by mid-September. Later pruning stimulates new growth during warm fall temperatures, and the plants will not have time to harden off before winter. This can increase the chance of freeze damage.
Hybrid tea and grandiflora roses should be cut back fairly hard in late August or early September. Other types of everblooming roses may also be pruned back one-third to one-half their height as needed to shape, stimulate vigorous new growth, remove dead or diseased canes, or control the size of the bush.
Our long growing season allows for the abundant growth of tropicals and tender perennials used as bedding plants in our gardens. In many cases, they look somewhat overgrown now, but they will continue to grow and bloom until October or early November. Now is an excellent time to trim them back or even cut them back fairly hard so they will be shapelier, fuller and not so tall for the fall-blooming period.
Popular bedding plants that benefit from trimming now include periwinkle, salvia, lantana, Mexican heather, blue daze, pentas, purslane, begonia, impatiens and ornamental peppers. How far back you prune them depends on how overgrown you think yours are. Generally, plants are cut back about one-third to one-half their height, but I have cut many of the plants listed above back farther with good results.
I have sizable plantings of blue plumbagos in my home landscape that are overgrowing the space allotted to them. I plan to prune them back by one-half of their height sometime this weekend as I know they will bounce back with new flushes of flowers as the fall season approaches.
I must admit this takes some determination and a strong will. Your plants will certainly not look their best immediately after the procedure. In many instances, though, it is well worth the down time. If some of these plants look overgrown now, think of how they will look by October. ?
William Johnson is a horticulturist with the Galveston County office of Texas A&M AgriLife Extension Service. Visit his website at aggie-horticulture.tamu.edu/galveston/index.htm.