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Extension > Garden > SULIS > Maintenance > Sustainable Lawncare Information Series > Weed Management > Control the Weeds or Start Over or Both

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Control the Weeds or Start Over or Both

It has been stated many times that a healthy, vigorous lawn is the best defense against weed invasion. Thin lawns and bare areas are the most common reasons for increased weed presence. Determining the reasons for a lawn’s sparseness or lack of vigor is the first step to managing the encroachment of weeds into the lawn. Table 10.6 lists a few causes for thin and sparse lawns. Figures 10.17 and 10.18 are two illustrations of the same conditions.

Table 10.6. Thin and Sparse Lawns

Sparse and bare areas can be caused by many reasons. Some of the more common ones are:

  • Grass species and/or varieties are not adapted to the particular site conditions or imposed maintenance program
  • Damage caused by animals, diseases, insects or people
  • Damage due to environmental stresses such as drought, shade, heat, cold, and poor drainage
  • Misuse of fertilizers and pesticides
  • Improper mowing height and/or frequency
  • Overuse of the lawn resulting in severely compacted and poorly aerated soils

Figure 10.17. Thin and sparse lawn – sunny area.

Figure 10.18. Thin and sparse lawn – shady area.

If the lawn care practices of mowing, watering, fertilizing and herbicide application have failed to reduce weed populations to less than 40 percent of the lawn surface, renovation may be the answer to restoring a healthy lawn. Table 10.7 discusses some things to consider before beginning a lawn renovation project.

Table 10.7. Criteria for Lawn Renovation

Renovation should be considered if any of the following conditions exist in your lawn:

  • Approximately 20-40% of the lawn is dead or has very sparse growth. This may be due to a variety of factors such as low soil fertility, drought and heat, insect damage, poor mowing practices, disease, moderate soil compaction, or increasing shade and competition from growing trees.
  • Lawn is soft and spongy when walking across it and responds poorly to regular watering and fertilizer applications. This condition usually indicates excessive thatch (greater than ½ inch). Thatch is a layer of partially decomposed grass stems, roots, and rhizomes (not leaves) at the soil surface but below the green vegetation.
  • Broad-leaved weeds such as dandelion, plantain, and knotweed, or grassy weeds such as crabgrass cover about 20-40% of the lawn area.

If it is determined that renovation should occur, see Chapter 6 Renovating an Existing Lawn to Achieve Sustainability for step-by-step renovation procedures.

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