Scarifying is best carried out in Spring or Autumn. The process will remove the majority of moss and thatch to enable water and fertilisers to reach the rootzone, it will also lift procumbent growth, thin the sward and reduce trailing weeds such as clover.
Excess thatch can cause surface rooting, therefore the grass will require constant feeding and watering due to lack of root depth. Without thatch removal the lawn can be very susceptible to browning during hot weather and diseases such as Red Thread will thrive. Moss will be dramatically reduced by scarifying but there is usually an underlying problem causing moss invasion, this needs to be addressed if moss return is to be prevented.
Heavy Autumn scarification may leave bare patches, these can be overseeded to prevent invasion of Annual Meadow Grass and weeds.
Verticutting during the growing season will help to reduce build up of thatch and on some lawns this may be a better alternative to annual scarification. It is good practice to verticut once per month during the growing season to thin the sward & lift trailing weeds which in turn will help prevent diseases and keep the sward in good order.
Please contact me if you would like additional information about lawn scarifying or verticutting.