Do grass clippings contribute to thatch?

    The most common issue people concern in grasscycling is letting the grass clipping lay on the lawn and not to bag them. Their concern is won't that contribute to thatch and make the lawn look bad? The answer to this question in a word is - NO!

    What is Thatch?
    Thatch is an intermingled organic layer of dead and living shoots, stems and roots that develops between the green vegetation and the soil surface. Thatch has high lignin content and resists microbial breakdown.

    What is Thatch? 

    Thatch may cause the following problems:
    • Thatch tends to shed water, preventing its infiltration and creating localized dry spots.
    • Thatch can minimize the movement of air and fertilizers into the soil layer weakening the turf and making it more susceptible to insect and disease problems.
    • Diseases are enhanced by thatch.
    • Thatch can provide an ideal environment for turf damaging insects. Thatch is an ideal layer for disease-causing organisms to produce spores and other infectious bodies and build up. Thatch is also reported to attract chinch bugs.

    Are there any benefits from thatch?
    A moderate level of one-quarter to one-half inch thickness has the following advantages:
    • The grass is more tolerant of wear.
    • The soil is less susceptible to compaction due to the cushioning effect.
    • The layer of thatch acts as a mulch preventing accelerated drying of the soil surface.

    Causes of Thatch
    Thatch accumulates because the growth of the roots, crowns and lateral stems exceeds their decomposition. Heavy nitrogen fertilizer applications or over watering frequently contribute to thatch, because they cause the lawn to grow excessively fast but prevents the development of those soil microbes responsible for the decomposition of thatch. Other factors that influence thatch and mat buildup include:
    • Soils with a pH above 7.2 or below 6.
    • Heavy and salty soils.
    • The use of fungicides and other pesticides that kill or impede the growth of soil microbes and earthworms.

    Do grass clippings contribute to thatch?
    In a word - NO! Clippings and thatch are simply not connected; research has shown that grass roots are the primary cause of thatch, not grass clippings. Thatch is composed mainly of roots, stems and crowns; it results from the abnormally fast growth of roots and other plant tissues and is caused by improper fertilizing and watering. These plant materials contain large amounts of lignin and decompose slowly.
    Grass clippings are very high in water content, approximately 85 percent water, with only small amounts of lignin, and decompose quickly leaving nitrogen and other beneficial nutrients for the turf.

    Grass clipping should be left on the lawn because:
    • Nitrogen and other nutrients in clippings are recycled into the lawn. An additional 1 to 2 pounds of nitrogen per 1000 square feet (.5 to 1 kg per 100 square meters), as well as supplemental potassium, will usually need to be added each season where the clippings are removed.
    • The decomposition of clippings encourages beneficial earthworms and microbes responsible for the breakdown of thatch.
    • Bagging of clipping will be reduced or eliminated - clippings may be collected on occasion to add to your compost pile.
    • The volume of yard waste that typically ends up at the local landfill is reduced by 25% by leaving grass clippings on the lawn. This helps preserve vital landfill space.