Fertilize, prune before colder weather

By Dan Gill

LSU AgCenter Horticulturist

We will soon begin to move into fall, and that influences what we do in the garden now. It’s time to finish up fertilizing a variety of landscape plants as well as time to prune many shrubs, cut back overgrown tropicals and trim some bedding plants.


You may fertilize your lawn, shrubs and ground covers that are still actively growing to encourage one last burst of growth. But do it now. As we move into fall and winter, it’s important for hardy plants in the landscape to begin to slow their growth and prepare for the coming cold and possibly freezing temperatures.

Fertilizer applied after early September, especially those with nitrogen, may encourage plants to continue actively growing into early winter. This increases the possibility of cold damage even to plants that would normally be hardy. It’s especially true for Louisiana because fall temperatures are generally mild and don’t give plants a strong signal to go dormant.

Apply granular fertilizer evenly to freshly mowed lawns and immediately water it in. Pay careful attention to the rate of application and use a fertilizer spreader to ensure even coverage. Calculate the square footage of the area to be fertilized by multiplying the length of the area by the width before you purchase your lawn fertilizer. That way you will know how much you need.

Shrubs and ground covers may be fertilized with a general-purpose fertilizer that has a 3:1:2 or 4:1:2 ratio – high first number, low middle number and a third number somewhere in between, such as 15-5-10 or 16-4-8. Sprinkle the fertilizer evenly in the bed where they are growing. With shrubs, you may also apply fertilizer around each plant.

You don’t necessarily need to 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, you have some plantings you have been intending to fertilize or you feel would benefit from fertilization to boost their vigor, now is the time to do it.

Pruning shrubs

Pruning is another activity that gardeners should focus on now. Spring-flowering trees and shrubs, such as azaleas, spireas, Indian hawthorns, cherries and Oriental magnolias, as well as early summer-flowering gardenias and hydrangeas, have already set their flower buds for next year and should not be pruned. Fall- and winter-blooming sasanquas and camellias also have set their flower buds. Extensive pruning of these plants from now until they bloom will diminish their flower display.

It is, however, OK to selectively remove specific shoots or branches to shape these plants without affecting the flowering of the remaining growth. Sometimes azaleas send out long shoots this time of year, and they can be pruned back to make the shrubs shapelier. Just don’t get carried away. If you feel more extensive pruning is critical, the sooner you do it, the better. But expect to see diminished flowering from those plants next year.

It’s also important to prune everblooming roses by early September to get them into shape for the fall blooming season. This can be done even if they are currently blooming. After a long summer of growth, most roses are rather overgrown. Cut the bush back to the desired height – usually 2 to 3 feet for hybrid teas and grandifloras. Make your pruning cuts right above the place where a leaf is or was attached to the cane. Remove all dead wood, diseased canes and twiggy growth.

Shear hedges

Hedges, such as ligustrum, boxwood, dwarf yaupon, photinia and viburnum, should receive their final shearing now through mid-September. Later pruning will stimulate new growth during warm fall temperatures, and the plants will not have time to harden off before winter, which increases the chance of freeze damage.

Trim back bedding plants

Our long growing season allows for the abundant growth of tender perennials used as bedding plants in our gardens. In many cases they look somewhat leggy and overgrown now, but they will continue to grow and bloom at least until November. If needed, now is an excellent time to trim them back so they will be more shapely, compact and attractive for the fall blooming period.

Popular bedding plants that benefit from trimming now include periwinkle, salvia, verbena, lantana, Mexican heather, coleus, blue daze, pentas, scaevola, purslane, begonia, impatiens and ornamental peppers. Generally, plants are cut back by about one-third of their height. After pruning, apply a fertilizer to stimulate vigorous new growth. Many perennials that have finished blooming may be cut back now as well.

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The numbers on a bag of fertilizer indicate the percentages of nutrients in the fertilizer. The first number represents nitrogen; the second number represents phosphorus; the third number represents potassium. Photo by Dan Gill

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Using a drop spreader helps ensure an even fertilizer application. Photo by Dan Gill

9/2/2016 3:29:05 PM
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