Water Repelling Soil in the Home Gardens: Causes, Signs, and Solutions Revealed!

What is water repelling or hydrophobic soil?

By definition hydrophobic means “lacking an affinity for water; insoluble in water; repelling water.”

I’m sure you have found your way here because when you’re watering the garden the water seems to run off or pool on top of the soil, not soaking in. Or maybe after heavy rain you think its the perfect time to get planting only to dig a shovel into your soil and find that under a centimetre of moist soil it is bone dry!

Australia has more than its fair share of water repelling soil due to our warm climate, inconsistent rainfall and ancient soils, which adversely affect soil quality. Hydrophobic soil is particularly prevalent in sandy soils, cheap or old potting mix, and soils containing hard to break down organic matter.

What causes hydrophobic soils.

Hydrophobia is caused by Australia’s hot climate and bush fires which disperses waxy compounds found in freshly fallen leaf litter layer. These waxy compounds bind to the soil/sand particles sealing them off and causing them to repel water. Soils that consist of larger particles like sand are more likely to be hydrophobic as it is are easier for the waxy compounds to fully coat them unlike particles such as clay or silt.

In the face of climate change and some scientists claiming that we are moving into the Pyrocene age (The ice age, but with fire) our hydrophobic soil issues are only going to get worse. Much worse. 


How do I know if I have water repellent soil?

Oh, my friend, you will know.
Struggling plants, water pooling on the surface, water beading on top of soil, water running off or after ‘deep watering’ only the first centimetre has any moisture in it at all.

If you would like to find out how bad your soil is , wet a patch of bare soil down. soil takes more than 1 minute to soak up water are slightly repellent. Soil that takes 10 minutes or more to soak in is considered severely repellent.

Hydrophobic soil can also be hidden under a layer of your mulch. Every once in a while scrape back some mulch and just make sure the water is actually penetrating down lower than the mulch layer. Wood chip mulches can actually create or exacerbate the problem if you aren’t vigilant.

How to fix hydrophobic soils? What we can do in our gardens?

There are a number of solutions to hydrophobic soil and often they work best in combination with each other. 

Compost & Manures
Ah Compost! Well rotted organic matter is always the answer!
Adding compost and manures to your hydrophobic soil will increase its water and nutrient holding capacity while promoting good microbial life in your soil. Hell, do it even if you don’t have hydrophobic soil!
If you cant make enough of your own, its best to buy large quantities of compost from a landscape supplier. Their compost is ofter cheaper and far superior then bagged products.

Use a soil wetting agent -

Organic Soil wetters can be harder to find but you should be able to purchase them from your local garden centre. They act as a detergent which breaks the surface tension of the water allowing it penetrate past the waxy coatings on the soil particles allowing water to penetrate deep into the soil and reach your plants roots. They work in the same way dishwashing liquid breaks down fats and oils in the kitchen sink. The ingredient in organic soil wetters is often Agar-agar which Is naturally derived from red algae its harmless to the environment and naturally breaks down in the soil.

In-organic soil wetters work well but are not sustainable long term and are not a match with organic gardening practices. They are made with alcohol or petroleum distillates, such as polyacrylamides. Which will cause more problems for your soil and plants with long term use. So organic is the way to go long term.

Make your own soil wetter? 

Yes!
Natural soaps are a great way to break surface tension. You should be incredibly careful with the soap you use. Castile liquid soap is a great option. Its biodegradable and completely safe for plants in very small amounts.

Mix up a watering can with your favourite seaweed solution or home made compost tea and add 1 teaspoon of Castile soap and go to town pouring it all over your soil.

One application generally won’t be enough of either type of soil wetter you’ll need to repeat every few weeks for the best results.

Claying -
Mixing clay through your water repellent soil may a great solution. particularly for very sandy soils as in Perth WA and beach side gardens.
If you are establishing a new garden this is the perfect time to get your soil right from the beginning. Clay can retain up to six times more water than sand.
As clay has larger surface area and loves to absorb and hold water. It acts by diluting the hydrophobic particles and when watered will disperse the water more evenly. An added benefit is that clay will hold nutrients in the soil making them more available to your plants.

When applying to soils, you must be careful to apply the correct ratio

The amazing thing about adding clay is that it has long term effects, the effects of clay will last in your soil for 30+ years. Now that’s bang for your buck!

The inclusion of any type of clay enhances your soil's capacity to retain water, although it does not prevent the soil from drying out.

Beads, Gels & Crystals

Soil wetter beads, gels and crystals are an option for potted plants. They have a strong chemical make up which excludes them from direct to garden. In potting mix they do work although, I would opt for a long soak in seaweed solution and top dress the pot with composted organic matter. If you know your potting mix is old the best option may be a re-pot with fresh quality potting mix.

Mix up your mulch.

Adding the same mulch constantly year after year to your garden beds will create a microbial monoculture which can bind the mulch together to become like a water proof mat on your soil. If your adding different types of mulches the material will attract different microbes and fungi to breaking it down making it less likely to mat and become hydrophobic over time.

Natures Way.

The Australian landscape has its own way of combatting soil hydrophobia. As a drought breaks and a deluge of rain falls over the landscape eucalyptus trees start to froth and foam, they look as though they crying detergent from their trunks.
Eucalyptus bark and leaves contain saponins such as glycosylated alkaloids or isoprenoids that create foam when mixed with rain water. Rather than emerging directly from the tree, these saponins accumulate on the surface of the tree. This foam breaks the surface tension of the rain water allowing it to penetrate deeper into the hydrophobic soils below.

You can see that Australia has a long history of drought and bushfires when our plant spices have evolved their own built in soil wetting agent.

Hydrophobia can be a big issue for Aussie gardens but there are ways around it. With a bit of effort and time you’ll build beautiful hydrophilic (opposite of hydrophobic) soil.