Scarifying
Conventional wisdom is that lawns (particularly couch varieties), need to be cut back hard once a year in summer to reduce the thatch which builds up under the greenery. The grass needs to be cut right back to ground level with a scarifier or vertical mower, and chicken manure then spread thickly over the surface.
Traditionally scarifiying (heavily cutting back the thatch) was done in summer, although there are advantages to doing it in mid-winter. Winter is a much more comfortable time of the year to do the job, without the summer heat to dry out lawn which may become initially stressed from the heavy cut. The lawn does take a little longer to regenerate in winter from scarifiying, but new grass should be growing through in about a month.
More frequent and light scarifying can often overcome the need for deep annual de-thatching. Earthworm activity can also be beneficial in reducing the build-up of lawn thatch since the worms eat their way through the mat of dead plant material. Worms can be encouraged by increasing the soil's pH level, relieving compaction and improving drainage, and by using organic forms of nitrogen such as urea. Avoiding the use of fungicides and weed reducing chemicals is also helpful in the build-up of worm populations.
Scarifying revitalises lawns by thinning the dense thatch, saving water and promoting new root growth for a healthy lawn.
Coring
If you've ever noticed the lawns at a bowling green, and wondered why they always look so much better than yours, the following steps are the ones used to get that degree of perfection. Coring is carried out by a specially developed machines.In the old days, (and still in use by some lawn maintenance people) a few holes were poked into a lawn with a fork. This method of coring creates small holes by compacting the area around the hole and thus compounding the problem of hard soils. The coring machine actually extracts plugs of soil at 2 to 3 inch intervals, to a depth of around three inches. By removing the plug to form a hole, water and nutrients are able to penetrate deep into the root system and when done regularly, can save up to 50% watering.