SERVICE Formation of thatching The reason behind unhealthy-looking, mostly pale green lawns whose growth stagnates despite fertilising and watering, which are often plagued by undesirable weeds or shallow-rooted poa, could well be thatching. Thatch is generally a dark-brown, clearly delineated layer of organic matter on the surface of the soil that has not decomposed. It comprises living and dead roots, offshoots and mowing residue as well as leaf and stem debris. Lawns with thatch layers are more vulnerable to fungal diseases. The turf is often very dense, but soft and spongy when wet. The roots don’t grow down into the soil, but rather spread out into the layer of thatch. This means no meshing with the actual turf-bearing layer. Thatching occurs primarily in sand-rich, acid soils with limited biological activity. It heavily restricts the water and nutrient permeability into the deeper zones and lessens the resilience of the grass cover. Some plant species such as red fescue, tall fescue and bentgrass are especially susceptible to thatching, whereas ryegrass and timothy barely form any. Bluegrass and annual and common meadowgrass are somewhere in between. Lawn thatching is also encouraged through the over-application of nitrogen fertilising, especially with physiologically acidic fertilisers such as ammonium sulphate. To prevent the formation of thatching, all measures that restrict the biological activity in the soil should be avoided. For example, repeated fungicide treatments could be the cause of an intensively expanding thatch layer. Under certain disadvantageous circumstances, a thatch layer of up to 1 cm can form within a year. A zone of up to 0.5 cm is not necessarily cause for concern. On areas subject to wear and tear, for example sports fields, it is even desirable, since it minimises erosion and protects the surface. On the other hand, layers of 1 to 2 cm in thickness can retain up to 20 l of water per m2, which in summer then uselessly evaporates. Moss One group of plants that is considered undesirable, especially in ornamental and home lawns, is moss. It appears in lawns mostly when the grass grows slowly, the soil is very wet or in the shade of buildings or, in particular, of trees and shrubs. Moss is also often caused by poor maintenance measures such as cutting grass too short and/or an insufficient supply of nutrients. A chemical treatment to counteract moss is also available. It usually contains iron(II)-sulphate. After the treatment, the moss becomes dark-brown or black and can be removed. Prevent new moss: To prevent new moss from forming, the grass should not be cut to below 4-5 cm (not under 5-6 cm in shaded areas) at weekly mowing intervals, and should be fertilised at least 3 times per year. If the moss cannot be kept at bay by mechanical means, chemical treatment is the last resort. There are a few reliable preparations or combinations of products that can be used on lawns. The range of available products is constantly changing. One way of keeping abreast is the Plant Protection Product Directory (Pflanzenschutzmittelverzeichnis) Part 2 (Cultivation of vegetables, fruits and decorative plants) from the German Federal Biological Research Centre for Agriculture and Forestry (BBA) in Braunschweig. It can be obtained from: Saphir Verlag, Gutsstrasse 15, 38551 Ribbesbüttel. NB: In this regard, please observe the legislation of the individual federal states. 1. strive for a soil pH value of at least 5.5 to 6.0 2. sow species that tend not to form thatching 3. do not overly fertilise with nitrogen 4. avoid any unnecessary chemical treatments 5. water less frequently with greater volumes of water that thoroughly soak the soil rather than more often with lesser amounts 6. take every possible measure for the biological activation of the soil TO SUMMARISE: 66
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