I’ve seen people use herbicides to control weeds in an old, declining lawn. Then, with all the weeds gone, the lawn’s owner suddenly realized that he or she had no lawn left.
Sometimes the best solution is to start over. Many older, thinning, declining, weedy lawns need to be reestablished. As lawns decline and thin, the weeds move in. When you reach the point where there is less than sixty percent desirable cover, reestablishment should be considered.
In the process of redoing a lawn, attempt to determine why the lawn declined and correct mismanagement practices that were contributing factors in the lawn’s demise.
Common causes for lawn decline:
Soil compaction – Mowing equipment, vehicles and foot traffic (from adults, children and pets) all result in the soil becoming compacted within a lawn. Compacted soil results in less water and oxygen getting to the lawn roots and less than favorable growing conditions for the roots.
Nutrient imbalances – Routine fertilization can result in some fertilizer elements building up to excessive levels while other elements may be lacking. It’s common to find high levels of phosphorus in older lawns. Phosphorus does not leach readily even in our sandy soils. Other elements such as potassium leach readily. Over time, we’ll end up with too much of some nutrients and too little of others, which contribute to growth difficulties and possible decline in our lawns.
Tree competition – Trees and larger shrubs can compete with a lawn. As a tree gets larger with time, it becomes more competitive with lawn grass. The tree’s demand for water and nutrients increases as it becomes larger. Its root area becomes more extensive and it progressively produces more shade. Lawns usually thin significantly in association with older, large trees and shrubs.
Root pests’ numbers may slowly build to damaging levels as a lawn ages. Some common examples include nematodes (microscopic roundworms), soil inhabiting fungi such as Gaeumannomyces and ground pearls (a scale insect found in soil).
Improper lawn maintenance practices may be a contributing factor in the decline of an older lawn. Common contributing factors to a lawn’s demise include routinely mowing too low, excessive fertilization and irrigating incorrectly.
Sometimes herbicides are only a “band aid” approach when dealing with an old, mismanaged lawn.
The following UF/IFAS Extension website link provides a wealth of information on growing a Florida lawn. http://hort.ufl.edu/yourfloridalawn
Larry Williams, UF/IFAS Extension Agent, Okaloosa County, March 29, 2012