September is time to prune and fertilize

Richard Bogren, Gill, Daniel J.

For Release On Or After 09/02/11

By Dan Gill
LSU AgCenter Horticulturist

In late summer gardeners need to think about two important points of landscape maintenance – fertilizing and pruning. This time of year is the latest we should fertilize lawns, hardy shrubs and ground covers in the landscape. Now is also the time to prune many shrubs, cut back overgrown tropicals and trim some bedding plants.


You may fertilize your lawn and shrubs or ground covers while they’re still actively growing to encourage one last burst of growth, but do so now.

As we move into winter, it is important for hardy landscape plants to begin to slow their growth and prepare for the coming cold and the possibility of freezing temperatures. After early September, fertilizer applications, especially with nitrogen, may keep plants actively growing into early winter. This increases the possibility of cold damage even to plants that would normally be hardy and is especially true in Louisiana because fall temperatures are generally mild and do not give plants a strong signal to go dormant.

Granular lawn fertilizers should be applied evenly to freshly mown lawns and immediately watered 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 of the area before you purchase your lawn fertilizer. That way you will know how much you need to buy.

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 the plants are growing. With shrubs you may also apply the fertilizer around each plant.

It’s not really necessary that you need to fertilize plants in your landscape now. If your lawn, shrubs and ground covers 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 meaning to fertilize or you feel would benefit from fertilization to boost their vigor, now, not later, is the time to do it.

Pruning shrubs

Pruning is another topic that gardeners need to 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 – already have set their flower buds for next year and should not be pruned. Fall- and winter-blooming sasanquas and camellias have also set their flower buds. Extensively pruning these plants from now on 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 it is critical to do more extensive pruning, the sooner you do it, the better. But expect to see diminished flowering from those plants next year.

It’s also important to prune ever-blooming 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. Pruning later will stimulate new growth during warm fall temperatures, and they won’t 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 about one-third 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.

Rick Bogren

8/30/2011 12:43:47 AM
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