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Thatch is the layer of dead and living organic matter that accumulates between your grass blades and the soil surface. A thin layer is normal and beneficial, but too much creates serious problems. Understanding what thatch is and how to manage it is essential for a healthy lawn.
What Exactly is Thatch?
Thatch consists of stems, roots, rhizomes, and other plant material that builds up faster than it decomposes. It’s not the same as grass clippings, which break down quickly. Thatch is tougher, more fibrous material that accumulates over time.
Look at a cross-section of your lawn. Between the green grass blades above and the soil below, you’ll see a layer of brown, spongy material. That’s thatch.
A thin layer of thatch, around 10mm or less, is actually beneficial. It insulates roots from temperature extremes, retains moisture, and provides some cushioning. Problems arise when this layer grows thicker.
How Thatch Builds Up
Thatch accumulates when organic matter is produced faster than soil organisms can break it down. Several factors contribute to this imbalance.
Grass species vary in their thatch production. Vigorous spreading grasses that produce lots of stems and runners tend to create more thatch than bunch-forming species.
Over-fertilising, particularly with nitrogen, promotes rapid top growth that outpaces the soil’s ability to decompose dead material.
Acidic soil conditions slow decomposition. The bacteria and fungi that break down organic matter work best in neutral to slightly alkaline conditions.
Compacted soil limits the activity of earthworms and microorganisms that would otherwise process dead material.
Frequent, shallow watering keeps the surface moist, encouraging shallow root growth and surface organic matter accumulation rather than deep rooting.
Problems Caused by Excessive Thatch
When thatch exceeds 15-20mm, it causes multiple issues.
Water can’t penetrate. Thick thatch acts like a sponge, absorbing water before it reaches the soil. Your lawn may wilt even after rain because moisture never reaches the roots.
Shallow rooting develops. Grass roots grow into the soft, moist thatch layer rather than down into soil. These shallow roots make grass vulnerable to drought and heat stress.
Disease and pests thrive. The damp, organic-rich thatch layer provides ideal conditions for fungal diseases and insect pests. Problems like red thread and fusarium often worsen in thatchy lawns.
Fertiliser and treatments don’t reach the soil. Products you apply sit in the thatch layer rather than reaching grass roots or soil, reducing their effectiveness.
The lawn feels spongy underfoot. Walking on thick thatch feels bouncy and soft rather than firm.
Checking Your Thatch Level
To measure thatch, cut a small plug from your lawn using a knife or trowel. Go deep enough to see the full profile from grass through thatch to soil.
Measure the brown, spongy layer between the green grass above and the actual soil below. Under 10mm is healthy. 10-15mm is moderate. Over 20mm needs attention.
You can also simply push your finger into the lawn. If it sinks into soft, spongy material before hitting firm soil, you likely have a thatch problem.
Removing Thatch: Scarification
The primary method for removing thatch is scarifying. This involves using blades or tines to cut through and pull up the thatch layer.
Powered scarifiers are most effective for thick thatch. Electric or petrol machines with rotating blades slice through the thatch and lift it to the surface for removal.
Hand raking works for light thatch but is hard work for significant accumulations. A spring-tine rake pulled firmly across the lawn will bring up loose thatch.
The best time to scarify is early autumn when grass is actively growing and can recover quickly. Spring is the second-best option. Avoid summer heat and winter dormancy.
What to Expect After Scarifying
Scarifying produces shocking amounts of debris. A typical lawn can yield several wheelbarrow loads of dead material.
Your lawn will look terrible immediately after scarifying. Bare soil, thin grass, and scratch marks are normal. Don’t panic, as this is expected and temporary.
Recovery takes 2-4 weeks with proper aftercare. Water well, feed to promote recovery, and overseed any thin areas. By the following month, the lawn should look better than before.
Preventing Thatch Build-up
Prevention is easier than cure. Good lawn care practices reduce thatch accumulation.
Regular aeration improves soil conditions and helps decomposition. Annual aeration keeps thatch in check on most lawns.
Balanced fertilising promotes steady, healthy growth rather than the rapid flushes that contribute to thatch. Follow a sensible feeding schedule rather than over-applying nitrogen.
Correct soil pH supports the organisms that break down organic matter. If your soil is very acidic, lime applications can help.
Deep, infrequent watering encourages deep rooting rather than surface growth. Shallow daily watering promotes the conditions that create thatch.
Light annual scarification prevents thatch building to problematic levels. A gentle pass with a rake or light scarifier setting removes accumulation before it becomes severe.
Thatch vs Moss
Thatch and moss often occur together but are different problems. Moss is a living plant that colonises lawns, particularly in shade, damp conditions, or where grass is weak.
Scarifying removes both thatch and moss, but the underlying causes differ. Treating moss requires addressing the conditions that favour it, shade, drainage, soil acidity, and grass health.
Our guide to removing moss covers this separately.
After Thatch Removal
Following scarification, help your lawn recover strongly.
Feed immediately after scarifying to promote recovery. A balanced fertiliser or specialist post-scarification product gives grass the nutrients it needs to regrow.
Overseed any thin or bare areas. Scarifying creates the perfect conditions for seed germination, with good soil contact and reduced competition from thatch.
Water regularly until new growth establishes. The exposed soil dries out faster than a thatchy lawn, so keep moisture levels up.
Maintain good practices going forward to prevent thatch returning to problem levels.
For more lawn care guides and seasonal advice, visit our complete lawn care guide.
Our Pre-Seed Foundation Feed is perfect for post-scarification recovery. High phosphorus promotes root development, helping grass re-establish quickly after the stress of thatch removal.
