Most fertile garden soils accept water and allow it to drain to lower soil depths. However, soil can occasionally become hydrophobic, resulting in water that pools at the uppermost surface instead of draining toward plant roots. Why does soil become hydrophobic, and how can you fix it?
Hydrophobic soil can be caused by dry conditions, clay and sand amendments, hydrophobic pesticides, and undecayed compost. Solutions include consistent watering, adding loam, washing out pesticides, and waiting for organic matter to decay.
This article will address each potential cause behind hydrophobic soil and discuss possible solutions. You can use this information to refresh and amend hydrophobic soil, making it ideal for plant life.
1. The Soil Is Suffering From Drought and Lack of Humidity
Dry, hot conditions can turn rich, loamy soil hydrophobic in a matter of days or weeks. If you’ve ever forgotten to water container plants during summer, you’re likely familiar with this phenomenon.
But how can high temperatures and dry air turn fertile soil into a hydrophobic substance? The answer lies in the decayed organic matter (humus) found in most loamy garden soils.
While the primary component of composted organic matter is cellulose (primarily plant cellulose), this nutrient-rich matter also contains resin, oils, and wax. These elements are naturally hydrophobic.
These components remain relatively homogenous in loamy soils when the weather is cool and wet. This means they’re equally spread throughout the dirt. However, when temperatures rise and the air becomes dry, these substances rise to the surface of the soil, forming a water-repelling layer.
The primary soil types that make up loamy soil (sand, clay, silt) also separate into distinct layers during hot, dry weather. Heavier soils, like clay and silt, can sink toward the bottom, allowing sand to rise toward the top.
These tiny grains are then coated in the water-repellent elements. This process transforms naturally porous sand into a fine-grained hydrophobic surface. Fortunately, solving this issue is typically as simple as mixing the soil types back together and adding a little water.
How To Fix
If your outdoor container plants or garden beds have started repelling water, several potential solutions exist.
One of the best options for container plants is a quick depotting (be sure to set the freed plant’s roots into a shallow dish of room-temperature water), followed by a re-mixing of the soil.
Follow these steps to thoroughly re-mix your plant’s soil:
- Remove the plant from the soil.
- Grab a spade, and mix the dirt like a delicious cake batter.
- After you’ve mixed the soil, be sure to crush any hardened clumps into tiny particles.
- Use a spray bottle full of water to give the dirt a liberal spritzing.
While some of the soil may still repel water, most of it should absorb the moisture and allow it to drain. You can also use a garden hose to wet the dirt, allowing up to one inch of water to collect at the top of the soil surface.
This excess water should begin to drain through the soil, rinsing away small amounts of wax and oil. You can repot the plant when the soil surface is no longer flooded.
To prevent the soil from drying out entirely in the future, you may want to install a sub-soil watering system for your potted plants.
Plant watering stakes are an excellent option. These ceramic stakes feature thin hoses that you can place into water bowls. When your container plant’s soil grows dry and brittle, these hoses suck up much-needed moisture to prevent hydrophobia. Even better, they release the moisture slowly, reducing the risk of root rot.
Refreshing hydrophobic soil in garden beds can be trickier, but it’s not impossible.
If you live somewhere that typically experiences hot, dry summers, you’ll likely want to outfit your garden beds with drip irrigation systems that can remain hidden beneath mulch or dirt. These keep sub-soils moist, even when surface soils begin to repel water.
2. There’s Excessive Sand in the Soil
If you’ve recently added clay and sand to your garden soil, you may have unwittingly increased its hydrophobic properties. Sandy soil, in particular, can become incredibly hydrophobic. This is especially true during bouts of hot, dry weather.
Natural waxes and oils rise to the surface when the weather is warm, forming a hydrophobic surface that repels water. Amending the sandy dirt with water-absorbing soils and fertilizers is a quick way to make sandy soils less hydrophobic.
How To Fix
If you’re working with sandy soil during the summertime, you’ll likely notice water pooling at the top of the soil’s surface. Luckily, fixing this issue may be as straightforward as adding some loamy garden soil or moisture-rich fertilizer.
Mixing dark, rich soils and fertilizers into sandy soils will help make your soil more receptive to moisture and imbue the dirt with life-sustaining nutrients. Remember, sandy soil is often nutrient-poor, so plants placed in the sand may struggle to thrive.
The primary exception to this is plants that prefer sandy, dry conditions, like cacti and succulents.
3. You’ve Been Using Hydrophobic Pesticides
Pesticides can help you repel pests, fungal spores, and weeds. However, they can also build up in the soil, forming hydrophobic layers to prevent water from reaching a plant’s roots.
Generally, pesticide chemicals that are highly absorbable (meaning they have a high Koc value) tend to generate the most noticeable hydrophobic effects.
Benomyl, a substance found in some fungicides, is one of the most notorious pesticides that can produce water-repellent soils. Malathion (a common insecticide) can also transform well-draining dirt into a hydrophobic substance.
Unfortunately, treating pesticide-laden soil can be challenging.
How To Fix
If you’ve been using chemical pesticides on your plants and soil, you may want to consider switching to all-nature alternatives. Not only can chemical pesticides build up in the soil (some take thousands of years to degrade), but they can also contaminate local groundwater supplies.
Soil that has absorbed several pesticides can also become toxic and infertile. Sadly, some soils are so contaminated that they can no longer support plant life.
Depending on the chemicals you’ve used (and the quantity you’ve applied), solving your pesticide-related soil hydrophobia could be as simple as waiting for the pesticides to degrade naturally.
If you’re concerned about the pesticide content in your garden soil, you may want to have it tested. You can request to have a soil sample analyzed by a lab to discover if pesticides are contributing to your garden’s suddenly hydrophobic qualities.
4. The Soil Contains Undecayed Organic Matter
While synthetic pesticides can contribute to hydrophobic conditions, organic matter may also be to blame. As mentioned earlier, the decayed organic matter found in loamy soil contains oils, resins, and waxes, all of which repel water.
However, undecayed organic matter (i.e., fresh compost material) can also make soil hydrophobic. In fact, organic matter that hasn’t yet rotted into a nutrient-rich mulch is far more likely to result in water-repellent soil than fully decomposed composts.
For example, soil that’s mixed with partially-decayed leaves can repel water. This is because the outer layer of the leaves may retain their wax, preventing water from quickly draining to lower soil layers.
The same is true of fruit peels, undecayed twigs, and other forms of organic compost. So, if you’ve been mixing partially-composted materials into your garden soil, you might find that the ground isn’t absorbing water like it used to.
How To Fix
There are two methods of fixing this issue, and both require patience.
The first way to resolve hydrophobic soil caused by undecayed matter is to wait for the organic materials to rot! You can expedite this process by spraying the ground with water daily. Though the water might initially settle onto the surface, it can speed up the decay of organic matter near the soil surface, eventually working its way down to deeper layers.
The second resolution requires a change in gardening habits. If you’ve been mixing partially-composted or raw organic materials into your garden beds, you’ll want to switch gears as soon as possible.
Allowing your compost to fully transform into a dark humus mix (with no identifiable components) can prevent a significant amount of hydrophobia. If you’re not currently using a composting bin, you may want to invest in one.
Adding a little water to the mix is a fantastic way to speed up decomposition, and excess water will drain away thanks to the ventilation openings. Your fresh, all-natural compost can be ready to use in two weeks, though decay rates vary depending on the materials you use.
Hydrophobic soil repels water, making it virtually impossible for moisture to reach a plant’s roots. Several things can cause soil to become hydrophobic.
Some of the most common factors contributing to soil hydrophobicity include prolonged exposure to dry environments, excessive amounts of clay and sand in the soil, usage of hydrophobic pesticides, and undecayed organic matter.
Transforming hydrophobic soil into fertile, well-draining soil may be as simple as wetting the soil consistently or amending it with loamy soil. However, you may need to flush the dirt of pesticides or wait for its organic matter to decompose.
You can read my other article on how to prevent soil erosion here: How to Prevent Soil Erosion for Gardening and Farming