Hydrophobic, or water repellant, soil is a problem that can hinder plant growth and health due to the fact that the plants cannot get access to sufficient water. Today, I am going to talk about what it is, what causes it and how to rectify the problem in your garden.
What is hydrophobic soil?
Hydrophobic soil is soil that prevents water from being absorbed into it. The water sits on the surface of the soil (eventually evaporating) and, if it does eventually soak into the soil profile, the water travels through pathways that are easy for it to travel through. This leaves a large amount of the soil within the garden bed bone dry, thus preventing plants from accessing the water they need.
What causes hydrophobic soil?
The water repellency of hydrophobic soil is caused by natural plant waxes that build up around individual soil particles. these waxes come from the natural process of plants biodegrading within the soil. Sandy soil is more prone to becoming water repellant than other soil types like clay or loam soils.
How do you turn hydrophobic soil into non-hydrophobic soil?
One quick fix for this problem is to use a wetting agent which removes the waxy layer off the soil particles and then allows the water to infiltrate the soil freely again. While useful to solve the problem initially, it is a short term solution to the problem as those waxy layers will come back over time.
A long-term solution to this water repellency is to start adding organic matter, like compost, to the soil. From doing some reading, many sources say that you should add mulch over the freshly added organic matter to prevent the soil from drying out. That is where I have to disagree with the advice because the soil is dry to begin with and mulch, as much as it can prevent water evaporating from the soil, it can also prevent water from entering the soil too. If you want to add mulch do so, but ensure the soil is wet first!
It is often said that having healthy soil is a great way to have healthy plants. This applies to hydrophobic soil as much for any other aspect of soil health.
Personal obeservations
My personal observations from when I have come across hydrophobic soils show a couple of things. The first thing I have always noticed is that there is very little, if any, sign of worms or other life in the soil. The next one is that there is very little organic matter in the soil, with none added to the soil in the previous few years. There are a few reasons for the fact that organic matter has not been added to these soils in this time period, if not longer and they are all equally infuriating and avoidable. They result from a system of landscape management that relies on getting the job done as quickly as possible for as little cost as possible-as long as it ‘looks’ like everything is healthy, its fine. That is a topic that can be talked about at length, but not right now!
The garden beds are also usually have bare soil in a fairly large percentage of it. Nature hates empty soil, which is why such areas often gain plenty of weeds. So, as well as adding organic matter yearly, get plants in there to cover the soil. I have never seen hydrophobic soils where there is little to no bare soil and plenty of organic matter in the soil.
In conclusion, to rectify your water repellant soils, you can use wetting agents initially to get water into the soil, but add organic matter (like compost, for example) to encourage soil life and structure to improve over time. Also have plenty of plants in your garden beds, keeping bare soil to a minimum. This also reduces the need for weeding-a rather dull task that most people dislike!
https://www.csiro.au/en/research/plants/crops/farming-systems/water-repellant-soils
https://blackdirtcompany.com/hydrophobic-soil-and-how-to-fix-it/