Do grass clippings contribute to thatch?

    The most common issue concerning people in grasscycling is letting the grass clippings lay on the lawn and not bagging them. Their concern is 'won't this 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 develop between the green vegetation and the soil surface. Thatch has high lignin content and resists microbial breakdown.


    Thatch may cause the following problems:
    • Thatch tends to shed water, preventing infiltration and creating localised dry spots.
    • Thatch can minimise the movement of air and fertilisers into the soil layer, weakening the turf, and making it more susceptible to insect and disease problems.
    • Diseases are enhanced by thatch.
    • 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 and tear.
    • The soil is less susceptible to compaction because of thatch's 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 exceed their decomposition rate. Heavy nitrogen fertiliser applications and over-watering frequently contribute to thatch; they cause the lawn to grow excessively but prevent the development of 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 fertilising and watering. These plant materials contain large amounts of lignin and decompose slowly. 
    Grass clippings are very high in water content, approximately 85 %, and contain only small amounts of lignin; they decompose quickly, leaving nitrogen and other beneficial nutrients for the turf.

    Grass clippings should be left on the lawn because: 
    • Nitrogen and other nutrients in clippings are recycled into the lawn. An additional 1 to 2 lbs of nitrogen per 1000 square feet (0.5 to 1 kg per 100 square meters), as well as supplemental potassium, will usually need to be added each season where the clippings have been removed.
    • The decomposition of clippings encourages beneficial earthworms and microbes responsible for the breakdown of thatch.
    • The bagging of clippings will be reduced or eliminated - clippings may occasionally be collected to add to your compost pile.
    • The volume of garden waste that typically ends up at the local landfill is reduced by 25% when leaving grass clippings are left on the lawn. This helps preserve vital landfill space.