Non wetting soil in lawns
Author: Stefan Palm Date Posted: 19 December 2018
I see a lot of people come into our store every day and ask, “why does my lawn have these dead patches in it?” While there are many reasons why a lawn can develop brown patches, the number one reason by far is non wetting soils.
A non wetting soil is where a soil repels moisture instead of absorbing it, like water on wax. The result is a generally uneven water distribution through the soil profile which leads to patchy and uneven lawn growth. You can literally have a green section of lawn right next to a brown one, even though you may water the area evenly. In that way, non wetting soils have a random, patchy effect on your lawn which is why it’s so often confused with beetle damage or fungal disease.
Water that lands on non-wetting soil doesnt sink in properly and either pools,runs off or evaporates rather than penetrating into the soil so no matter how much you water it, the water doesn’t make it to where it’s needed which means your lawn suffers from drought stress. Not only that, since water is the carrier of nutrient to your lawn’s root zone, lawns growing on non wetting soils are often nutrient deficient, shallow rooted and susceptible to disease. The irony is, even though your lawn may look like it needs a drink – more water, more fertiliser and more beetle killer won’t solve a non wetting soil.
What Causes it?
In most cases, non-wetting soils are caused up by the build up of organic residues. These residues are a waxy like substance that coat the soil particles which in turn cause it to repel water. Organic residues occur when organic material in the soil breaks down over time. Fungi in the soil can also lead to excessive build up of organic residues.
Identifying water repellence.
In a domestic lawn situation, water repellence can be identified in 2 ways.
- The presence of a general patchiness in your lawn, with the soil being dry despite regular watering. This can be an all over uniform dryness or a random patchiness where you have brown patches amongst a green lawn.
- How long it takes for a droplet of water to penetrate the soil surface
The simple way to test for a water repellent soil is to take a 100mm deep core sample of soil from a green area in your lawn and another from a brown area. (If there are no green areas, just take a single sample from a dead or dying area). Firstly, do a visual check – If the green sample has moist soil and the brown sample has dry soil, you know you have a non wetting soil problem. A secondary check is to apply a drop or two of water to the side of a dry soil sample. If it takes more than 5 seconds to penetrate, then this would confirm you have a problem.
How do you treat it?
The best way to treat non wetting soils in a domestic lawn is with liquid wetting agents (not solid wetting agents) Liquid wetting agents do a couple of things – they help break down the waxy organic residues and they also coat the soil in an agent which makes the soil much more receptive to holding onto water molecules. In that way they treat the soil. Unfortunately, you can’t really solve water repellent issues in soil indefinitely, you can only ever treat them. Wetting agents don’t last very long in the soil and you will find that in time, they need to be re-applied. The good news is that they are cheap to buy and available at most hardware stores. An interesting aside is that there are many types of wetting agents, some lasting longer than others and some having the ability to actually store water in the soil – but that’s the topic for another blog!
In my opinion, liquid wetting agents are the elixir of life for lawns and garden, whether you have non wetting soil or not. They ensure that any rain or water penetrates evenly. They also reduce wastage of water because they make it possible for the water to penetrate quickly instead of evaporating or running off.
For what it’s worth, if you find yourself with a patchy lawn, the first thing I’d recommend is a wetting agent!