Hydrophobic soil isn’t soil that’s afraid of water! It is soil, or dirt, that repels water not allowing water to soak in.
Healthy soil with a balanced and diverse microbial population doesn’t tend to get hydrophobic. So healthy soil microbes living in healthy soil help prevent water repellence.
What are the signs and symptoms of hydrophobic soil?
There are some sure signs indicating a hydrophobic soil. Here’s some things to look for:
It’s dry. It’s dry to the touch and dry for any plants living/existing in it.
There might be patchy growth: If you’re out in the field and you notice patchy growth to grasses, crops and other plants: there may be a hydrophobic soil forming. Evidence of some sick plants among other healthy plants can be a sign of hydrophobic soils.
Lack of germination: Irregular seed germination is another indicator of hydrophobic soils. This is particularly noticeable where you have spread a lot of seed and some patches fail to germinate.
Dehydrated plants despite rain or irrigation. Where plants appear to be wilting and dehydrating despite having access to water.
Ponding is another indicator of hydrophobic soil. Ponding is where water sits on top of the soil surface for a significant period of time. Even a small amount of water ponds on a hydrophobic soil.
A few drops of water added to a hydrophobic soil will tend to result in those drops getting coated in a sandy substance. The actual drops get coated with soil particles. I often detect hydrophobic soil whilst conducting a pH test – the drops of solution roll off the soil sample and the liquid itself can get covered in particles.
Suffering pot plants appearing to drink water. Pot plant soils can become hydrophobic. When we water pot plants the water may appear to soak into the soil, but sometimes, it seeps down the sides of the pot completely bypassing the roots.
Wood chips or pine bark as a mulch can indicate hydrophobic soil.
What causes hydrophobic soil?
There are a number of factors causing hydrophobic soil. Some fungi consume organic materials and coat soil particles, particularly sand particles, with a waxy coating. Over time this waxy coating becomes like a rain coat for the soil.
Some plants have naturally waxy compounds in them. When they die down, when they are mulched, or when they are cut down, their decomposition can contribute to soil particles being coated with a waxy substance that repels water.
Another contributing factor to hydrophobic soil is sandy soil. In particular it’s a sandy soil composed of less then 10% of clay. Clay soils are less likely to be hydrophobic but there are exceptions.
Sometimes clay and silty soil form extremely tight aggregates (chunks of soil holding together). These aggregates can become coated in a hydrophobic substance and start repelling water.
The key cause of water repellent soil is a lack of humus and organic matter. Soil that is full of waxy coating fungi is a soil that lacks microbial diversity. To get that diversity, we need organic matter. Read my blog called: How to make healthy soil – transforming dirt into soil to learn more about this process.
How do we test for hydrophobic soil?
We can tell that a soil is hydrophobic by this simple test (or watch the video):
Pour water on the soil/dirt. If it’s a pot plant, just pour enough water into the pot to bring the water to the brim of the pot.
Monitor – does the water sit on the surface and form a pond? Does some of the dirt particles move to the top of the water and thus coating it? If we’re talking about a pot plant: does the water run down the sides of the pot? Are we sure?
Once the water has subsided, using our finger or a digging tool or a stick, move part of the top layer of soil aside and look. Sometimes we only need to move 5mm of soil and sometimes we need to move 3cm of soil. Is it dry? Is there a horizontal line in the soil where it is wet and then suddenly dry?
Pour more water onto that area you just uncovered.
Does it pond? How long does it take for the water to soak in or disappear from the surface?
Once the water has disappeared from the surface, again move part of the soil you just poured water onto aside. Is it dry underneath? If it is, it’s repelling water. If its still dry, its hydrophobic soil.
Fixing hydrophobic soil
For fixing hydrophobic soil in pot plants read my blog specific to that: Dry pot plants: fixing hydrophobic soil in pot plants. Also note that when we turn dirt into soil we can prevent hydrophobic soil from occurring in the first place.
Where we have plants in the ground and we find we have hydrophobic soil, there are some things we can do to alleviate the problem short of digging up the plant.
We’ll want to add an organic liquid soil wetter to deal with the fungal problem first. To learn more about soil wetters read my blog Dry pot plants: fixing hydrophobic soil in pot plants. That blog covers soil wetters. Our aim is to transform our dry soil into a moist soil full of microbes and worms.
So we need food for those creatures. We need organic matter. Compost of various types are excellent. Read my blog on How to make healthy soil – transforming dirt into soil for more information on what else we need to add: organic matter and rock minerals in particular.
First, we can dig up the top layer of soil (up to 10cm deep) around the plant. Typically when soil has been hydrophobic for some time, this area of soil will be fairly root free. If it is full of roots, don’t disturb them. Pour on the diluted organic liquid soil wetting agent. Cover as much of the root zone as possible.
Typically the root zone will extend the distance of the outer leaves. So if the shrub is 2 metres wide, the root zone may also extend that distance.
Add your organic matter and rock minerals and mix it in with the existing soil as best you can. We can then water that in. Check to see if the water is penetrating the soil using the steps above. Make a mental note. Cover the area with a mulch (sugarcane is good). Water the mulch and water the root zone fairly well.
Check the soil in a couple of days. Scratch around and see if the water is penetrating the previously hydrated soil. If it’s still showing signs of dryness, you might like to add another mix of diluted liquid organic soil wetter.
Once we’ve added the organic matter and ingredients listed here, including the mulch, try not to let the soil dry out completely.