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August is Your Last Chance to Prune and Fertilize Many Plants
by Dan Gill
by Dan Gill


Dan Gill earned B.S. and M.S. degrees in horticulture from Louisiana State University in Baton Rouge, and is an Associate Professor in Consumer Horticulture with the LSU AgCenter.

He is the spokesperson for the LSU AgCenter’s Get It Growing project, a statewide educational effort in home horticulture utilizing radio, Internet, TV and newsprint. Gardeners throughout Louisiana read his columns in local newspapers, watch his gardening segments on local TV stations and listen to him on local radio. In the New Orleans area, Dan appears weekly on the Channel 4 Morning News, writes a weekly gardening column for The Times-Picayune and hosts the Saturday morning WWWL Garden Show, a live call-in radio program.

Dan is co-author of the Louisiana Gardener’s Guide and author of Month-by-Month Gardening in Louisiana. His “South Louisiana Region Report” and “Only in Louisiana” columns appear monthly in the Louisiana Gardener Magazine.

August 19, 2012

August is a month when gardeners should think about two important aspects of landscape maintenance – fertilizing and pruning. This month is the latest we fertilize lawns, 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 time to stop pruning spring-flowering trees and shrubs.

You can use granular, general-purpose fertilizers for most fertilizing jobs in the landscape. These fertilizers are relatively inexpensive and easy to use. They provide an immediate release of nutrients and then continue to feed for about six to eight weeks thereafter. If you feel you need to fertilize your lawn, shrubs or ground covers to encourage one last burst of growth, it’s important to do so now. Applications made this month will continue to feed until October, after which time it is not appropriate for hardy plants to continue to receive supplemental nutrients.

This is because as we move into the winter, it is important for hardy plants in the landscape to slow their growth and prepare for the coming cold. 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 us in Louisiana, since fall temperatures are generally warm to mild and do not give plants a strong signal to go dormant.

For lawns, granular fertilizers 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 very 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 the fertilizer in the bed where they are growing. You also may apply the fertilizer by sprinkling it around each plant. The size of the shrub is a factor in determining the amount of fertilizer to use. Rates are generally higher for larger shrubs, but check package recommendations for specific amounts.

It’s not necessary that you should go out and fertilize plants in your landscape now. If your lawn, shrubs and ground cover plantings look healthy and have grown well this summer, there would be little indication that fertilizer would be needed. If, on the other hand, there are some plantings that you have been meaning to fertilize or that you feel would benefit from fertilization to boost their vigor, it’s time to do it now – not later.

Pruning is another activity gardeners need to focus on at this time. Fall-, winter- and spring-flowering trees and shrubs – those that bloom from November through April, such as sasanquas, camellias, azaleas, spireas, Indian hawthorns, cherries and Oriental magnolias, as well as summer-flowering gardenias and hydrangeas – have already set their buds for flowering next year. Extensively pruning or cutting back these plants from now on will generally diminish or eliminate their flower display. It’s alright 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 that will not have time to harden off before winter, and 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 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, scaevola, 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.

Pruning 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.

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