Do You Have Hydrophobic Soil? Here's How to Check & Fix It Fast Before Plants Die From Thirst
Hydrophobic soil is often misdiagnosed as a drainage problem, but it's more serious than that. Here's how to check if soil is hydrophobic and fix the problem.
You water the bed then watch it pool on the surface and slide off without absorbing. It looks like a technique problem or a compaction issue, but it’s usually neither. Hydrophobic soil is likely the cause.
Hydrophobic soil is common in containers, sandy beds, and anywhere that’s been left to dry out hard for long enough. But hydrophobic soil hasn’t just dried out. It has changed at the particle level, developing a coating that sheds water the way a waxed car sheds rain – and watering more won’t fix it.
Understanding the different types of soil helps explain why some kinds are more vulnerable to this issue than others. But the short version is that almost any soil that dries out too fast or too much can turn hydrophobic. Luckily, this problem is easily diagnosable and you can fix it with items you probably have on hand. If left unchecked, though, it could kill plants. Here's how to avoid that dire outcome.
Article continues belowWhat Causes Hydrophobic Soil?
Hydrophobic soil begins with organic matter drying out past a critical point and leaving a water-repelling film on individual soil particles. Two things are usually responsible for this.
Certain fungi produce hydrophobics as a part of their normal biology. When soil dries out enough, those waxy compounds build up on particle surfaces and stay there. Plant resins and decomposing organic materials do something similar, leaving a waxy residue behind as they break down. The particles end up coated, and coated particles shed water. The worse the drying, the thicker the coating.
Sandy soils are the most prone to this problem because they have low organic matter and dry quickly. Peat-based potting mixes are very vulnerable, which seems a bit counterintuitive because peat is often marketed for its water retention. But once it fully desiccates, it becomes one of the most stubborn types of hydrophobic soil.
Mulched gardens are prone to this problem, too. The mulch layer itself can dry out and form a crust that sheds water before any of it reaches the soil underneath. Pouring on more water doesn’t help because volume isn’t the issue. The soil surface refuses to let water through and down to the plant roots.
How to Test for Hydrophobic Soil
Before reaching for a fix, it’s worth ruling out soil compaction or poor drainage as the actual culprit of water-repelling soil. Testing for hydrophobic soil only takes a minute. Scrape back any mulch, let the surface breathe, and then place a single drop of water on the soil and watch.
Healthy, well-draining soil will absorb the water fast – the droplet should instantly disappear. Hydrophobic soil won’t absorb the water. The drop will hold its shape and sit there on the soil surface. Still there after 60 seconds? That’s your answer. It’s not draining slowly, it’s being rejected by the soil.
Check a few spots rather than calling it from just one drop. Hydrophobicity is rarely uniform. A badly affected patch can sit right next to one that’s fine, depending on where organic matter built up or where drying hit hardest.
The depth of the issue is worth checking, too. The surface may absorb normally, but a repellent layer could sit just below. This shows up as water pooling just below the soil surface when you dig down after watering.
What You Will Need
Biodegradable soap helps fix hydrophobia without hurting beneficial soil microbes.
This ergonomic watering can makes watering easy on you and plants.
Break up severely hydrophobic soil with a strong garden fork like this.
How to Fix Hydrophobic Soil
For a moderate case of hydrophobic soil, diluting soap in water is the quickest solution. The soapy water works as a surfactant, cutting the surface tension that lets the waxy coating shed water and suddenly the soil starts accepting moisture again.
Three or four drops of a biodegradable liquid soap, like this one from Amazon, in a full watering can is enough to do the job. Stick to a fragrance-free, biodegradable formula. Standard dish soap in small amounts is fine, but anything with heavy degreasers or added chemicals can knock back the healthy soil biology you want to preserve.
Apply it slowly over the affected area and let it work in rather than flooding the surface. One or two passes usually breaks the barrier. A long-reach watering can, like this one from Amazon, makes applying the solution slowly and precisely easier, especially in tighter beds where it's hard to control the flow.
Severe cases of hydrophobic soil need a physical fix first. A sturdy garden fork, like this one from Amazon, is the right tool for the job. It gives you enough leverage to break the crust without digging up established roots in the process.
Push your fork into the soil alongside the affected area and work it back and forth to crack the hydrophobic crust. You don’t have to turn the soil deeply, just enough to open the surface and give water somewhere to go.
Once the soil starts accepting moisture again, work in a layer of organic compost, like this from Amazon, to finish the job. Compost reintroduces the microbial activity that keeps hydrophobic soil from happening again and adds organic matter that holds water rather than shedding it.
