Over the years, even a well-maintained lawn produces thatch. It is made of undecomposed grass stems, blades, roots and rhizomes, which collect between the green vegetative part of the lawn and the soil. Several factors make for a faster build-up of thatch – heavy, compacted soil, inadequate soil preparation prior to seeding, excess of undecayed organic matter, grass sown too densely, incorrect fertilisation and mowing. The build-up of thatch starts when dead grass and other organic remnants accumulate faster than they decompose naturally.
A thin layer of thatch causes no particular damage, quite on the contrary – it traps moisture thus reducing the need to water the lawn. It also reduces soil temperature fluctuations. However, an excessive layer of thatch prevents water from penetrating the soil, absorbs nutrients, impedes growth of new grass, all of which affects the lawn, and it often stays yellow for a very long time in spring. If the soil is very heavy and compacted, thatch only worsens the situation – it sticks to the soil thus creating a solid layer, which is impermeable to water and air. Grass roots start to grow more shallowly, lawn becomes susceptible to traffic damage, frost, drought and riddled with diseases.
An excessive layer of thatch must be raked and removed every year. Special rakes or scarifiers (electric, petrol) are used for this purpose. These are compact machines, which resemble lawnmowers, and are often wrongly referred to as aerators. Special blades rake out thatch and moss, cutting up any lumps in the process.
Rake the lawn in early spring, depending on the weather (late March to early April) before the growing season. This must be done in dry weather, since wet grass sticks to the rake tines or the scarifier blades. If grass was not mown in the autumn, now it has to be cut on the lowest setting. The scarifier blades have to be lowered so that they would remove thatch and slice the soil simultaneously. Lawns are almost never completely even, so the height of blades must be constantly monitored and adjusted. The raked out thatch is collected into a special scarifier container, so if thatch is very thick it fills up quite quickly. It might be a better idea to rake out thatch without collecting it and leave to dry for a while. Raked out and dry thatch can be easily collected with an ordinary garden rake. Collect it into bags and remove from the garden, or else you can put it on a compost heap.
Having removed the thatch, fertilise the lawn, which is best done just before the rain. If the soil is very compacted and heavy it is advisable to aerate it as well. A household scarifier costs in the area of 600 lt, and since it is used only once a year, budget-minded gardeners might consider renting scarifiers and aerators. Most companies trading in garden tools and machinery often offer them for rent.
© Giedra Bartas, 2011