Many lawns deteriorate from poor maintenance, inadequate drainage, heavy traffic, pest problems, weed invasions, or simply because the wrong grass species was planted.
Where lawn quality is unacceptable, renovation may be necessary. Renovation involves planting grass seed into an existing lawn area, often adding new grass varieties to repair damage or increase tolerance to drought, shade, or wear. Renovation usually isn’t necessary until approximately 20-25% of the lawn is bare or covered with weeds. Renovation alone will not be sufficient if problems are too severe. Starting a new lawn may be the best option where removal of the existing turf, tilling, adding topsoil, and changing the soil grade are needed. The following conditions may warrant starting over:
* an excessively compacted soil
* greater than 50% weeds or bare soil
* a thatch problem (discussed later) that isn’t corrected by renovation efforts
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.
The 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.
What is thatch?
Thatch is the layer of living and dead stems, roots, stolons, and rhizomes between the green blades of grass and the soil surface. A thin layer of thatch (less than 1/2 inch thick) can be beneficial to the lawn because it helps to limit weed germination, reduce water evaporation, and protect from frost damage. However, thick thatch layers can prevent water, air, and nutrients from penetrating the soil, causing reduced root growth and increased potential for drought stress. Thatch also favors fungal growth and can harbor insect pests. Some turfgrass species, such as tall fescue and perennial ryegrass, do not produce much thatch. Other turfgrass species, such as bermudagrass, bentgrass, and Kentucky bluegrass, have creeping growth habits and rapidly build thick thatch layers.
If your lawn has a bouncy feel to it when you walk on it, thatch is probably building up. As a general rule, plan to dethatch your lawn when the thickness of the thatch is more than 1/2 inch deep. To determine the thickness, remove a small square of your lawn to a depth of about 3 inches and measure the brown layer between the grass blades and the soil surface.
For both cool and warm-season grasses, the best time to dethatch is mid-to-late spring or early fall. During this time when the turf is actively growing, the grass will quickly recover from injury.
The frequency of thatch removal depends upon how fast the thatch layer builds. Lawns that are overwatered, overfertilized, or growing on heavy clay soils may accumulate thatch quickly. Turfgrass species is also a factor. Grasses such as bermudagrass, bentgrass, and Kentucky bluegrass build a thick thatch layer over several months and may need to be dethatched yearly. Grasses such as tall fescue and perennial ryegrass do not produce much thatch and may not need to be dethatched more than every few years.
Heavy clay soils or soils with heavy foot or equipment traffic often become compacted over time. Soil particles are pressed close together, restricting the movement of oxygen, nutrients, and water to the lawn. As a result, the turfgrass grows slowly and poorly. Turfgrass grown in compacted soils soon become susceptible to drought, disease, and insect damage.
How to alleviate soil compaction
Aerating the soil removes small cores of soil from the lawn, allowing air, water, and nutrients to penetrate the soil.
In general, if you see areas damaged from too much traffic or if water puddles on your lawn or runs off without soaking in, your soil may be compacted and you need to aerate your lawn. Aerify your soil during the spring when grasses are actively growing. Avoid aerifying during the summer months when high temperatures may be detrimental to lawns.
The frequency of aeration depends on soil type, how the turfgrass is used, and its expected appearance. Heavy clay soils need to be aerated a couple of times a year while sandy soils may only need aeration once a year. Lawns with very high traffic may need to be aerated several times a year. For lawns with little or no activity, aeration may not be needed.