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By Jeff Floyd
Certified horticulturist and arborist
Controlling weeds while they are small is easier and less expensive than trying to get rid of them after they have matured. One of the best ways to control them involves fertilizing and watering the yard properly to give lawn grass a competitive advantage. In flowerbeds, maintaining a three- or four-inch layer of wood chip mulch is an attractive way to suppress weeds. However, in both flowerbeds and lawns, pre-emergent herbicides should be your number one choice to prevent weeds.
Fall and spring temperatures are ideal for weed seed development. Therefore, the months of February and September are excellent times to apply these preventative herbicides in anticipation of weed development. The active ingredients in pre-emergents disrupt the growth of very young cells but has little effect on cells that are less vigorous.
Weeds seedlings are dependent upon actively dividing cells located at their root and shoot tips to get established. Pre-emergents often stop cellular division and effectively short-circuit the growth of young weeds. In this sense they are selective, only harming young tender plants. Even their misuse is not likely to destroy your lawn. Pre-emergents have little if any effect on mature plants because established trees, shrubs and grasses are not entirely dependent upon rapidly dividing cells to stay alive.
On the other hand, the use of a post emergent is more likely to result in accidental damage to desirable landscape plants. The injury caused by many post-emergent herbicides is not isolated to seedlings. For example, glyphosate, which is the active ingredient in Roundup, kills plants by stopping the production of an essential protein that virtually all plants require. Misuse of glyphosate can lead to the wholesale destruction of any plant it contacts.
Labor Day and Valentine’s Day are simple to remember and excellent dates for applying pre-emergents. Granular pre-emergents are readily available in home improvement stores and garden centers. This formulation is easy to use because it can be applied with a common fertilizer spreader.
If you decide to get out this Labor Day and apply a granular pre-emergent, as with all herbicides, read and follow the label directions. It’s the law.