Non wetting soil in lawns
Author: Stefan Palm Date Posted: 11 November 2020
I see a lot of people come into our store every day and ask, “why does my lawn have 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 very dry lawn root zone even though you may be watering every day. Even the best types of soils don't wet evenly. Some areas absorb water deep into the profile, while other areas in the same patch of lawn completely repel it. Wherever a soil repels water, you can be sure that the lawn growing in it will be patchy. You can literally have a brown section of lawn right next to a green 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 doesn't 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
With the glorious thunder storm we had this week accompanied by around 5-10mm of rain, it's a good time to test how well your soil absorbs water. You can test this yourself by going out onto your lawn with a trowel and dig out a small 100mm core from a green area 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 is dry, you know you have a non wetting soil problem since the whole are was doused with the same amount of rain. A secondary check would be 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.
Statistically speaking, for every 100 core samples of turf we see, 45 of them have water repellent soils. That means that around 45% of all dead or patchy lawns in South Australia are caused primarily by soils that won't absorb water!
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 break the surface tension of the water, allowing it to penetrate into 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!
Apply a hose on wetting agent such as Paul Munns Betta Wet in November and January every year. If you can't find Betta Wet, most liquid wetting agents you can find in hardware stores will do the job.
Water Retention Agent:
Once you have applied a wetting agent, apply a water retention agent such as SST Bi-Agra. Also available in a hose on pack, Bi-Agra is designed to hold water in the soil profile. A wetting agent enables water to get into the soil. A water retention agent ensures it stays there.
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 you do is apply a wetting agent!
Rejuvenating a kikuyu lawnBy: Don Buick on 15 February 2019How and when do I rejuvenate an old kikuyu lawn with lots of thatch.
Paul Munns Instant Lawn Response
Hey Don, Most of the thatch of a kikuyu lawn can be removed with a lawn . The goal is remove as much of the thatch as possible - in other words, the shorter, the better. The best time to do it is between October and March. Have a look at this blog for more info: https://www.paulmunnsinstantlawn.com.au/blog/scarifying-your-lawn/
Creeping oxalisBy: Henry Polec on 27 December 2018I have creeping oxalis in my lawn. Could you please tell me how to control it. What are the chemicals in it.
Paul Munns Instant Lawn Response
Hey Henry, Creeping oxalis is a really tough weed to selectively control in lawns. The key to success is using the right selective herbicide and being prepared to spray at regular intervals until the weed is under control. Its not uncommon to have to spray at 3 weekly intervals for up to 6 months to get on top of it. As you've probably already discovered, it has a tendency to bounce back! I would recommend using Amgrow Bindie selective herbicide combined with Heiniger Wetter and spreader for best results. The wetter and spreader sticks the chemical to the weed to ensure best results. Its a critical element to getting on top of this weed. Both these products are available on our website
Lawn ClarityBy: David Moore on 26 December 2018Thanks for a straightforward and clear article on lawn patches. Particularly in recommending a liquid wetting agent. I have used one, but will be getting more soon.