Caring, repairing and top dressing your lawn
Top dressing your lawn has a number of benefits. It helps keep the lawn level, can improve soil structure, stimulate growth and improve drainage. Top dressing is normally carried out in late spring or autumn - sometimes after aeration and scarification (see below). Top dressing has the added benefit of helping to prevent the build up of thatch. Thatch is a layer of living and dead stem stems, leaves and roots, that is normally beneficial, unless it becomes too thick. The topdressing helps encourage its breakdown by soil micro-organisms.
If a patch of turf becomes worn, it should be roughened up with a rake in spring or autumn and re-sown. Lawn repair mix can be used where additional soil is needed and will provide a good medium for grass seeds to germinate. Hollows in the lawn can be repaired by lifting the turf and then backfilling with lawn repair mix. The piece of turf is then replaced and rolled flat. Remember when filling the hollow that loose soil will compact down.
A compacted lawn can be aerated by making holes in the surface to bring in fresh oxygen and improve drainage. Specialist equipment is available for this e.g a wheeled spiker or hollow-tined fork, alternatively or an ordinary garden fork can be used by plunging it about 10cm into the earth.
A build-up of thatch (a thick layer of brown springy material) in your lawn can be detrimental to it. This should be done in Autumn by raking the turf through using a spring-tined, splayed-head rake (or a motorised scarifier if you have a large garden). If you have a moss problem however, this should be dealt with beforehand as scarifying can spread the moss around. Scarifying only removes a small proportion of the thatch (about 30%), so is it best to prevent build-up in the first place. Thatch is caused by incorrect fertilisation when new grass grows before the dead grass and other organic matter can be broken down by mico-organisms .
Mowing helps promote growth and encourages a thick, dense lawn. It also helps keep weeds down. A longer lawn, however, has more surface area for photosynthesis resulting in more plant growth. It also has a more extensive root system; short grass will suffer more in dry weather.