Dethatching and Scarifying Your Lawn: When and How

A thick, spongy lawn might feel great underfoot, but that bounce is often a warning sign. Underneath the green there is usually a layer of dead stems and runners called thatch, and once it builds up too far it starts to choke your lawn. Dethatching is how you clear it out and let the lawn breathe again. Done at the right time, dethatching can turn a tired, spongy lawn into a healthy one that soaks up water and feed properly. Here is everything you need to know about dethatching and scarifying, and how to do it without setting your lawn back.

Thatch is the spongy layer of dead and living stems, roots and runners that sits between the green leaf and the soil. A thin layer, up to about a centimetre, is completely normal and even helpful, insulating the soil and cushioning wear. The problem starts when it builds up thicker than that, and that is when dethatching earns its place.

A heavy thatch layer acts like a barrier. Water, air, fertiliser and nutrients struggle to get through to the roots, so the lawn dries out, gets hungry and starts rooting into the thatch instead of the soil. It also harbours pests and disease and makes the lawn scalp easily when you mow. That is the point where dethatching becomes worth doing, and where a bit of dethatching pays off fast.

Not every lawn needs dethatching, and doing it when it is not needed just causes unnecessary stress. Look for these signs before you reach for a rake or scarifier.

• A soft, spongy feel. If the lawn feels bouncy or springy underfoot, there is likely a thick thatch layer building up.

• Water runs off. When water beads and runs away instead of soaking in, thatch may be blocking it from reaching the soil.

• The lawn scalps easily. If the mower keeps exposing brown, stemmy patches, the grass is sitting up on a layer of thatch.

• It looks thin despite feeding. A lawn that stays hungry no matter how much you fertilise may have the feed trapped in the thatch.

• Check the depth. Cut a small wedge out with a knife and look. More than about a centimetre of brown, matted material means it is time for dethatching.

TIP: Give the lawn a good water a day or two before dethatching. Slightly moist grass and soil tear less and recover faster than a bone dry lawn, and the thatch lifts out more cleanly.

Timing is everything, because dethatching is a stress on the lawn and it needs to be growing strongly to bounce back. For warm season lawns like couch, kikuyu, buffalo and zoysia, the sweet spot is spring through early summer, once the soil has warmed up and growth has taken off. That gives the lawn months of good growing weather to recover and fill back in.

• Avoid the cooler months or a hot, dry spell. The lawn is either dormant or already stressed and cannot recover.

• Do not scarify hard late in the season, roughly after January, as there is not enough warm growing time left for the lawn to knit back together before winter.

Dethatching can be as simple as a thatching rake for a small lawn, or a powered dethatcher or scarifier for a bigger one. Scarifying is the more aggressive version, using vertical blades that cut down into the thatch, while a rake or dethatcher lifts the looser surface layer. Match the tool to how much thatch you actually have.

1. Start by mowing the lawn a little lower than usual.

2. Then work across it in rows, and go over it a second time at right angles if the layer is heavy.

3. Rake up and remove all the loosened material, since leaving it on defeats the purpose.

4. Go gently on soft leaf buffalo, which does not like being cut back hard, and only lift the dead leaf rather than scalping it.

5. Couch and kikuyu are tougher and recover quickly from a harder scarify.

A lawn always looks worse right after dethatching, and that is completely normal. The recovery is where dethatching pays you back, so give it what it needs. Water it in well and keep it moist while the new growth comes through.

This is also the perfect time to feed, because everything you apply now reaches the soil instead of getting stuck in the thatch. A seaweed tonic like Pure Seaweed+ helps the lawn shrug off the stress of dethatching and pushes strong root growth, while a high nitrogen fertiliser like Dominate or Pure Balance drives the fresh, thick growth that fills the lawn back in. With warmth, water and feed, most lawns bounce back within two to three weeks of dethatching.

Dethatching looks brutal on the day, but it is one of the best things you can do for a tired, spongy lawn. Clear out the built up thatch at the right time of year, match the tool to the job, go easy on buffalo, then feed and water well, and your lawn will come back thicker and healthier than before. Do it only when the thatch calls for it and dethatching becomes a reset button for the whole lawn.

Want to know exactly when to tackle jobs like dethatching through the year? Download our Free Lawn Calendar. It maps out every seasonal task, with the right products for each one.