Hydrophobic soil is a common issue in Australia, our hot climate and unreliable rainfall can cause havoc on our soil. Hydrophobic soil occurs when a waxy residue builds up on the soil particles resulting in it repelling water rather than absorbing it. It is most common in sandy soils, dried out potting mix and soils containing unrotted organic matter. You can identify hydrophobic soil by watering it. If water runs off or pools on the surface leaving the soil underneath dry, you've got Hydrophobic soil. Luckily, it is not too hard to fix, here's a few common ways you can improve your soil to make it water loving, or 'hydrophilic'.
Wetting agents are a great quick fix but will not resolve the issue long term. Wetting agents work by breaking down waxy coatings as well as breaking the surface tension in the water making it easier to penetrate the soil. Commercial wetting agents are available at garden centres, or you can make one at home using agar (powdered kelp)*. It is possible to use diluted dishwashing liquid or dish water/laundry water as a soil wetter, the surfactants in the detergent act to break the surface tension in the water in a similar way to wetting agents (use caution when using detergents on your garden, be sure to use environmentally friendly/biodegradable options and check their suitability for use on your specific plant varieties).
A better, long-term way to improve your soil is by adding well rotted organic matter, then mulching over the top to help prevent the soil from drying out. This will introduce microorganisms to your soil which will break down the waxy residue and also improve your soil biology. Just be wary of continuously using pine bark or eucalypt woodchip mulches as these can carry a fungi which negatively impacts soil conditioning. Varying the mulch used on your garden each application not only breaks the fungi cycle but helps to increase the microbiology within your soil as the mulch breaks down. Renowned horticulturalist Jerry Coleby-Williams recommends 'Succession mulching' - varying the mulch between mushroom compost, pine bark, composted lawn clippings, teatree and sugarcane mulches in that order, this will build a wide range of microbes to condition and aerate your soil. More is not always better, care must be taken when using mulches to make sure they aren't too thick and don't form a crust on top of your garden which will negatively affect the ability for water to reach the soil. We suggest a mulch thickness of between 3 and 5cm.
You can hydrate potplant soil by placing the pot into a tub of water so that the water covers the entire pot. Add half-strength liquid fertiliser to the water, this will add nutrients back into the soil. You should notice bubbles coming to the surface, soak the pot for at least 10-20 minutes. Potplants also require repotting occasionally, add new potting mix when repotting to boost moisture levels and provide fresh nutrients. The use of water crystals can also be beneficial to boost the water holding capacity of potplant soil.
Garden bed design
Flat garden beds are more likely to hold water than sloped garden beds when watered, giving pooled water a better chance to eventually soak in. If you can't make your garden beds flat then use furrows (trenches) in your garden bed, these will slow the water and help focus the water to stay near your plants rather than running off causing water loss and erosion.
*Agar soil wetter recipe:
Here's a recipe to make your own natural Agar soil wetter at home: Mix agar powder/powdered kelp (available at health food stores) and 500ml boiling water until you get the consistency of thick custard. Add this mixture to a 9 litre watering can and fill with water to dilute the mixture. Apply this over well watered soil. This should cover about 9m2 of soil. Ensure the soil is well watered before applying this mixture as this will allow for the best penetration of the wetter mix. Due to the biodegradable nature of this mix, it will only be effective for around one month.