Best Management Practices - Pruning and Mowing

Allen D. Owings, Bush, Edward W., Trawick, Robert C.  |  3/22/2005 7:07:25 AM

Pruning Your Ornamentals

Proper pruning is one of the most neglected and misunderstood of all gardening practices, yet it is one of the most important best management practices in a home landscape when done properly. Pruning is a skill and an art. It is a skill in making cuts that properly callus over to seal off the wound from disease and infection and an art in making the right cuts in the right places to get the plant to take on a more pleasing form. Pruning should be practiced as a vital part of the maintenance program for all shrub and tree plantings. Most shrubs will require some pruning annually and may require special attention to correct defects caused by mechanical injury or attack by insects and diseases. Trees need to be properly trained during their early years and pruned occasionally as they mature.

Reasons to prune:

  • To remove dead, diseased and other unwanted wood
  • To reduce plant size to manageable proportions
  • To maintain size and form for planting design specifications
  • To rejuvenate old plants
  • To produce improved flower quality

Most tree and shrub pruning operations can be taken care of with four basic tools. These include a small pruning saw, lopper shears, hedge shears and hand shears. Use the proper tool for the job. High quality tools are a good investment and will last for many years if properly maintained. Pruning saws are used for branches larger than 1 ½ inches in diameter. Pruning saws have narrower blades with coarse teeth that are designed to cut on the pull stroke. Hedge shears are used for shearing hedges or formally shaped plants. Hedge shears are not satisfactory for other pruning purposes. Lopping shears are designed to cut branches 3/4 to 1 ½ inches in diameter. Hand shears are used for the smallest cuts and for working with annual and perennial flowers.

Emergency pruning may be done any time a problem arises. The keys to successful pruning are timing, location of the cuts, how the cuts are made and the amount of wood removed. Pruning for flowering shrubs depends on the time of the bloom. Prune late winter and spring flowering shrubs after they flower. If spring flowering shrubs are pruned during the winter, flower buds will be removed. Examples in this category include azalea, spirea, mock orange, quince, hydrangea, weigelia, forsythia, gardenia, camellia, viburnum, deutzia and flowering almond.

Summer flowering shrubs are pruned from mid to late winter, before spring growth. Some plants in this group are crape myrtle, oleander, vitex and althea. Most evergreens not selected for flowering should be pruned in the dormant (winter) season, but some pruning may be done throughout the year.

No rules cover all pruning. The important consideration should be preserving the natural form of a particular species. The extent of annual pruning will depend on the plant. Some shrubs may require the removal of a considerable amount of wood each year, while others require little pruning. It is much better to prune lightly each year rather than severely butcher a plant after several years of growth. When pruning, first remove weak and spindly wood inside or near the ground. Next reduce the height of the plant to the desired level by making cuts at various levels, always keeping in mind the natural form of the plant. One rule for cane-type plants like nandina and mahonia is to remove one-third of the oldest and tallest canes near the ground each year. This will keep the height of the plant at a reasonable level. It was once believed that pruning cuts, especially large ones, needed to be painted with special pruning compounds to prevent the entry of insects and diseases. It is now known that these compounds can cause the plant more harm than good. Make all large cuts on the outside of the shoulder wrinkle to promote callus and healing. Cuts made flush with a primary branch or central trunk remove this shoulder wrinkle and healing over never occurs, leaving your plant susceptible to insects and diseases. Several special plant types or categories need special treatment for specific training purposes. These include espaliered plants, topiary work or “poodled” plants and other landscape oddities. They may have some appeal in landscape, and special reference books should be consulted on the subject.

An important best management practice in the annual and perennial flower garden is dead-heading. This is a pruning process that removes old flowers to encourage the plants to continue producing flowers. This is also very beneficial in the rose garden.

Mowing Your Lawn

Mowing has a measurable effect on the way a grass plant grows. The ability of a grass to sustain itself through frequent close clipping is one factor that distinguishes a grass species as a turfgrass. Grasses such as wheat, corn and oats cannot tolerate the harsh treatment of frequent mowing.

How often should a turf be mowed? The rate of growth and the height of cut determine the frequency of mowing. The rate of growth depends on the type of grass, soil fertility (especially nitrogen content) and the weather. Lawns in Louisiana are warm-season grasses. These grasses grow faster and need to be mowed more frequently in the hot summer if moisture is adequate. A general rule is to mow before the grass becomes one and a half times as tall as the cutting height of your mower. Or another way to say this is: Do not remove more than one–third of the grass top at any one clipping. For example, if the height of cut is 1 inch, mow when growth reaches 1½ inches in height. If you continually allow your grass to grow too tall between mowings, a thin, weedy turf may develop.

You can decrease the frequency of mowing by: (1) choosing a slower growing turfgrass, (2) reducing the rate of nitrogen fertilization and (3) raising the cutting height of your mower. The rate of nitrogen fertilization and the frequency and height of cut are major factors that determine the quality of turf.

Mowing height depends on the type of grass, your objectives and your willingness to work. Most people now mow with rotary mowers. These mowers have horizontal blades that flail the grass and fray the leaf blades. A rotary mower becomes noticeably duller after a few cuts and should be sharpened as needed. Some tough grasses like the zoysia will dull a blade quickly. Reel mowers have clean, scissorslike cuts and produce a better quality turf than do rotary mowers. A reel mower is more difficult to sharpen, but it should require less frequent sharpening. A reel mower may be more expensive, but it is normally more rugged and uses less fuel. Most reel mowers are particularly recommended for bermuda and zoysia grasses. A smooth turf, free of sticks, stone and other debris, is necessary when using a reel mower.

Removal of turfgrass clippings is not necessary if you mow as recommended. Research has shown that moderate amounts of small clippings decompose rapidly in warm weather with good moisture. Nutrients in the clippings are recycled without contributing greatly to the thatch layer. Nitrogen fertilization can be reduced if clippings are not removed. Clippings should be removed if they form clumps on the surface. Clumping normally occurs only if the grass is allowed to grow too high before mowing or if mowed when wet. Zoysia and centipede leaves do not decay as readily as leaves of other grasses, so clippings need to be collected and discarded when growth is rapid – especially with zoysia.

BMP Checklist:

  • Identify your lawn species.
  • Mow at recommended heights.
  • Keep mower blades sharp.
  • Prune trees and shrubs according to LSU AgCenter BMP recommendations.
  • Dead-head bedding plants and herbaceous perennials to encourage rebloom.
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