(also known as: things you wouldn’t know unless you were on this web site)

* Is thatch on the lawn good or bad? A quarter-inch layer of thatch on the soil surface isn’t bad, so it’s good as long as it doesn’t get any thicker. When thatch gets around three-quarters of an inch, it’s bad. Why? Thatch causes water problems, it restricts the movement of fertilizers and pesticides into the soil, it quickly becomes a haven for turfgrass insects, and it sometimes perpetuates the incidence of diseases that kill grasses.

* Where does thatch come from? Not where you most expect it. Grass blades contain sugar and water, therefore they decompose quickly during the mowing season; ordinarily, clippings will decay in 10-14 days. To make thatch, organic matter must contain the enzyme lignin. You find lignin in the stems and stalks of grass plants, in virtually all broadleaf weeds and obnoxious grasses (crabgrass, etc.). Lignin is the structural backbone of many plant parts, including annuals, perennials, groundcovers, herbs and vegetables. Lignin imparts strength and structure for plants. Organic matter (plant parts) containing lignin take an eternity to decompose because traditional insects are unable to feed on lignified plant material, and lignin happens to be toxic for bacteria which would ordinarily feed on organic matter containing lignin.

* How to reduce thatch? Biological products on the market (and there have been dozens) have not been successful at eliminating thatch. Light applications of composted cow manure to the lawn during summer months have suppressed thatch somewhat, but not eliminated thatch altogether. The best way of reducing thatch is to reduce the fertilizer applied to the lawn, also to make frequent but light applications of pulverized or pelleted limestone to the lawn (no matter what the soil pH tests reveal).

* When should you leave grass clippings behind on the lawn? Because bacteria are responsible for decaying organic matter (changing grass clippings to humus), we need to adjust our mowing practices to coincide when bacteria are working on the lawn. Bacteria function only as long as soil temperatures are above 53 degrees. When soil temperatures fall below 53 degrees, bacteria go to sleep. By this schedule, we should be bagging clippings first thing in the spring (late March onward). By late April and early May, soil temperatures have climbed above 53 degrees, so clippings should be left on the lawn as food for beneficial bacteria. The practice continues until early October when temperatures start to decline. When daytime readings fall into the low 60’s, bacteria are on the verge of going dormant, so clippings should be bagged from then on.

* What’s the benefit of leaving clippings on the lawn? It’s a question of how many clippings are left behind. Clippings contain minuscule amounts of nitrogen, phosphorus and potassium, so the dividends depend on the weight of grass clippings left behind. Some examples:

Clippings - Nitrogen - Phosphorus - Potassium

2 lbs. - 3.8 lbs - 0.44 lbs - 2.4 lbs
4 - 4.3 lbs - 0.44 lbs - 2.6 lbs
8 - 5.2 lbs - 0.48 lbs - 2.9 lbs

* What are the seeding rates for the different grasses? Grasses have been developed for different parts of the nation because environments differ from region to region. Today, grasses are generally divided into “cool-season grasses” and “warm-season grasses.” The seeding rates for grasses differ markedly. Here are seeding rates for the different grasses, assuming you were seeding 1,000 square feet of a new lawn:

Kentucky bluegrass: 1 – 1.5 pounds
Perennial ryegrass: 8 – 10 pounds
Tall fescue: 8 – 10 pounds
Chewings fescue: 3.5 – 4.5 pounds
Creeping red fescue: 3.5 – 4.5 pounds
Hard fescue: 3.5 – 4.5 pounds
Annual ryegrass: 6 – 10 pounds
Bermudagrass: 1 – 1.5 pounds (also with plugs)
Bahiagrass: 7 – 10 pounds
Zoysia grass: 2 – 3 pounds (also with plugs)