Why does one part of my lawn stay dry however much I water it?
Hydrophobic soil — why dried-out organic matter starts repelling water, how to prove it with a spade, and the aeration and wetting routine that actually rewets it.
- Difficulty
- intermediate
- Time
- 1 hr
- Read
- 4 min
Short answer
Soil that has dried past a certain point becomes water-repellent, so watering runs off or straight down the cracks and never wets the root zone. Cut a wedge and look: if the surface is wet and the soil 30mm down is dust dry, that is dry patch. Aerate, then water slowly and repeatedly, with a wetting agent if needed.
This is the problem where someone waters a patch every evening for a fortnight and it stays brown while the rest of the lawn is fine. Organic matter and fungal residues in the soil form waxy coatings when severely dried, and those coatings repel water. Once established, the patch dries faster than everywhere else each time, so it gets worse every summer rather than better.
What you'll need
- A spade
- A garden fork or hollow-tine aerator
- A wetting agent or a drop of washing-up liquid in a can (optional)
- Sandy loam top dressing (optional)
- Grass seed
Step by step
- Prove it with a spade before treating it.Water the patch, wait an hour, then cut a wedge of turf out. If the top few millimetres are damp and the soil below is powder dry, the water is not getting in. That is the whole diagnosis.
- Rule out the alternatives.A buried slab, rubble or a concrete footing under the turf gives the same brown patch with dry soil above it — dig and find out. A fairy ring gives a dry band in a curve. Grubs give turf that lifts like a carpet.
- Look at where it is.South-facing slopes, thin soil over rubble, sandy patches, the strip beside a hot wall, and mounds standing proud of the rest are the usual sites. Anywhere that dries first will become hydrophobic first.
- Aerate the patch thoroughly.Fork it deeply every 100mm, rocking to open the holes, or hollow-tine it. The holes give water a route past the repellent layer instead of over it.
- Water slowly, in several passes.A watering can dribbled over the patch, allowed to soak for twenty minutes, then repeated three or four times, achieves more than a hose left running, which will simply run off.
- Use a wetting agent, or a very dilute detergent as a stopgap.Wetting agents reduce the surface tension so water can penetrate the waxy coating. A few drops of washing-up liquid in a full can is the household version — it works, but do not overdo it, and do not use it where the run-off goes into a pond.
- Keep it wet once you have wetted it.The critical thing is never letting it dry to that point again. Water this patch before you water the rest, and more often, for the rest of the season.
- Top-dress and overseed the bare areas.Brush sandy loam into the tine holes, which improves the surface's ability to hold and release moisture, and sow seed into the bare ground before weeds get there.
- Raise the mowing height over the affected area.Longer leaf shades the soil surface and slows drying. On a lawn with a chronic dry patch this is the cheapest permanent improvement.
Tips
- Water in the early morning or evening so less evaporates before it soaks, and water this patch first while your attention and the can are full.
- A mulching mower helps here — returning fine clippings adds organic matter that holds moisture, provided the lawn is not already thatchy.
- If the patch is over a buried slab there is no watering routine that will fix it. Lift the turf and take the obstruction out, or plant something else there.
Common mistakes
- Watering more heavily and more quickly — Water applied fast to repellent soil runs off sideways or down the cracks. Slow and repeated beats heavy and fast every time.
- Assuming the patch is diseased — It looks like disease and is not. The spade test takes two minutes and tells you which it is.
- Letting it dry out again the following June — Hydrophobicity is easier to prevent than to reverse. Once you know where the patch is, it needs pre-emptive watering every summer.
If it doesn't work
Surface damp, soil dry 30mm down
Cause: Hydrophobic dry patch — Fix: Aerate, apply a wetting agent, water slowly in repeated passes and keep it damp.
Brown patch over a hard obstruction
Cause: Buried slab, rubble or footing — Fix: Lift the turf, remove or break up the obstruction, add topsoil and re-turf.
Dry curved band with a green ring
Cause: Type 1 fairy ring — Fix: Same aeration and wetting routine, but expect it to migrate outwards each year.
Water pools then runs off downhill
Cause: Slope plus repellency — Fix: Aerate across the slope, apply less water more often, and consider a small dished contour to hold water where it is needed.
Questions people ask
Is dry patch a disease?
No. Some fungi contribute to the waxy coatings involved, but the problem is a physical one — the soil will not accept water. Fungicides are irrelevant and unnecessary.
Does washing-up liquid harm the lawn?
Very dilute and occasional, it is a workable stopgap. Repeated or strong applications can scorch the leaf and are not good for soil life, and run-off should never reach a pond, where detergent is harmful to fish and amphibians. A proper turf wetting agent is better if the problem is annual.
Will it come back next summer?
Almost certainly, unless you water that area pre-emptively and keep the mowing height up. The patch dries first every year, so it is always the first to go repellent again.