Aerating vs. scarifying: the difference and when you need which
Almost everyone knows scarifying, far fewer people know aerating. Yet the two methods work in completely different places: the scarifier takes care of the surface, the aerator takes care of the soil below. Here you can read what each method does, when you need which one and how to combine them.
In short
- Scarifying removes moss and thatch from the surface. It treats the symptom.
- Aerating relieves compaction in the root zone. It changes the conditions in which moss and thatch develop.
- Raking out with spring tines is the gentle option for in between.
- Best time for both: late August to early October, in spring from about mid April.
- Combined: scarify first, then aerate, top-dress with sand and overseed.
The three methods compared
| Raking out | Scarifying | Aerating | |
|---|---|---|---|
| Tool | spring tines | rotating or fixed blades | spoons (hollow or solid) |
| Working depth | surface, thatch layer | thatch layer, a few millimetres into the soil | about 6 to 10 cm |
| Acts on | loose thatch, moss, clipping residues | compacted thatch and moss | compaction, air and water balance in the root zone |
| Stress for the lawn | low | high, the lawn often looks bare afterwards | low to medium |
| How often | several times a season | only when needed, usually once a year at most | once or twice a year |
Scarifying: what it can and cannot do
When scarifying, blades pass vertically through the sward and comb out moss and thatch. Thatch is a layer of dead runners, roots and plant residues between the blades of grass and the soil. A thin layer does no harm. Once it gets thicker than about one centimetre, it keeps water and air away from the soil and the lawn becomes susceptible.
Scarifying clears this up quickly. But it does not change why moss and thatch formed in the first place. If the soil is compacted and water drains poorly, both come back. Scarifying is also a harsh intervention. The sward is damaged and needs a few weeks to recover. You should overseed bare patches afterwards.
When to scarify?
- When moss or a clear thatch layer has formed. You can check this with your fingers: if the lawn feels spongy, there is too much thatch.
- When the lawn is growing well, i.e. in spring from about mid April or in late summer.
- Not in heat and drought, and not on wet soil.
By the way, fine clippings from mulching are not the cause of thatch. More on this in Mulching your lawn.
Aerating: tackling the cause
When aerating, spoons go about 6 to 10 centimetres into the soil. Hollow spoons pull out small soil cores. The compacted soil gets air again, water can seep down and the roots find space. If the holes are then filled with sand, the channels stay open for good.
Many problems on the surface originate in the soil. Compacted, poorly aerated soil holds water at the top, soil life works more slowly and breaks down organic material less well. The grasses root shallowly and become weak, and moss spreads.
Moss is not always about the soil, though. Shade, acidic soil or a lack of nutrients also encourage it. If you want to get rid of moss for good, it is worth looking at all the causes. How waterlogging develops and what helps against it is explained in Waterlogged lawn.
Hollow spoon or solid spoon?
There are two systems for aerating, with different jobs.
| Hollow spoon | Solid spoon | |
|---|---|---|
| How it works | pulls out soil cores | pushes the soil to the side |
| Strength | true soil exchange, lasting drainage with sand | quick, no cores, no sand needed |
| Typical use | thorough treatment, heavy and compacted soils | regular aeration in between, also during the season |
Both systems have their place. The hollow spoon is the tool for the thorough treatment, because it really removes soil. The solid spoon displaces the soil instead of removing it. That is a different application: it opens the surface quickly and lets air and water in. Spiking followed by top-dressing with sand also moves the lawn forward and is much better than doing nothing.
Raking out: gentle care for in between
A lawn rake with spring tines combs loose thatch, moss and clipping residues out of the sward without cutting it. Used regularly during the season, it prevents a compacted thatch layer from forming in the first place. If you rake out regularly, you need to scarify much less often.
Which method when?
| Problem | What helps |
|---|---|
| Loose thatch, some moss | rake out, several times a season |
| Compacted thatch layer over about 1 cm, a lot of moss | scarify, then overseed |
| Water stands after rain, soil hard, lawn thin | aerate with hollow spoons and top-dress with sand |
| Water beads off after a drought | aerate so water soaks in again |
| Moss returns every year | check the causes: compaction, shade, pH, feeding |
Why late summer is the best time for the thorough treatment is explained in Why September is the best month for lawn renovation.
Combining scarifying and aerating
If the lawn needs both, do everything in one go:
- Mow as short as possible and remove the clippings.
- Scarify and rake up the combed-out material thoroughly.
- Aerate with hollow spoons and collect the soil cores.
- Top-dress with sand: spread washed quartz sand and distribute it with the levelling rake.
- Overseed and work the seed in with the drag mat. Then keep moist.
More on the individual steps in Lawn aeration, Top-dressing your lawn with sand and Sowing a lawn.
Good to know
After top-dressing, put the reel mower aside for a few weeks. Grains of sand on the surface blunt the reel and bottom blade. Until the sand has been worked in, it is better to mow with a rotary mower.
Frequently asked questions
Do I have to scarify every year?
No. Scarifying is only needed if moss or a compacted thatch layer has formed. If you rake out regularly and aerate once a year, you often do not need it at all.
Can aerating replace scarifying?
Not completely. Aerating does not remove thatch from the surface. But it ensures that thatch is broken down faster and moss has poorer conditions. In the long run this makes scarifying necessary less often.
How often should I aerate?
Once a year, ideally in late summer. On heavy, intensively used soils, additionally in spring.
What do I do with the soil cores?
Collect them. Leaving them to crumble is possible on light soils, but on compacted loamy soils you would only bring the soil back to the surface.
Tools
- Lawnpecker: aerating with hollow spoons.
- Solid tine set for the Lawnpecker: aerating with solid spoons in between.
- REWUKIL: lawn rake with spring tines against thatch and moss.
- Levelling rake and drag mat: spreading and working in sand.
