Daniel Gill, Merrill, Thomas A.
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. It also is 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 that are still actively growing to encourage one last burst of growth, but do so now. As we move into the winter, it is important for hardy plants in the landscape to begin to slow growth and to prepare for the coming cold and the possibility of freezes.
Fertilizer applications made after early September, especially with nitrogen, may keep plants actively growing into early winter. This increases the possibility of cold damage even to plants that normally would be hardy – especially since our fall temperatures generally are 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 go out to 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 they are growing. With shrubs you also may apply the fertilizer around each plant.
I am not necessarily saying that you need to 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 you have been meaning to fertilize or that you feel would benefit from fertilization to boost their vigor, now is the time to do it, not later.
Pruning is another topic 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, have already set their flower buds for flowering 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 on will diminish their flower display.
It is OK, however, 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 also is 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.
Hedges, such as ligustrum, boxwood, dwarf yaupon, photinia and viburnum, should receive their final shearing now through mid-September. Pruning any later will stimulate new growth during warm fall weather. But that growth 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, these plants are cut back about one-third their height. After pruning, apply a fertilizer to stimulate vigorous new growth.
In addition, many perennials that have finished blooming may be cut back now as well.
Get It Growing is a weekly feature on home lawn and garden topics prepared by experts in the LSU AgCenter. For more information on such topics, contact your parish LSU AgCenter Extension office or visit our Web site at www.lsuagcenter.com. A wide range of publications and a variety of other resources are available.