Scarifying rips out the moss and matted dead grass (thatch) that smother a sward, so air, water and light reach the soil again. It’s for mossy, spongy paddocks, lawns and amenity grass where the grass has gone thin underneath.
A tractor-mounted scarifier has rows of rigid or spring tines, or rotating blades, that cut into the surface and drag out moss and thatch. It works much harder than a chain harrow, which only lifts the loosest material.
It leaves a lot of debris. On lawns and amenity areas that material is usually raked or collected; on paddocks it may be left to dry and harrowed in, or gathered up if there is a lot of it.
The field will look scruffy, even brown, for a few weeks afterwards. That is normal. Scarifying is very often followed straight away by overseeding, because the opened surface makes an ideal seedbed.
Early autumn, around September, is the classic time: the grass is still growing strongly enough to recover and there’s moisture in the ground. Spring, once growth has started, is the second choice, and is lighter-touch.
Avoid scarifying in hot, dry weather or when the grass isn’t growing — it won’t recover, and weeds will fill the gaps. Very wet ground tears rather than scratches.