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I LOVE the term hydrophobic soil so much. I love words and language and the implication that soil is scared of water.
This isn’t the literal case here (I ASSUME??), but when you’re watering your plant and yet the soil doesn’t seem to be absorbing the water, you could have hydrophobic soil.
One of the problems I’ve come across when trying to learn about remedying hydrophobic soil in house plants specifically, is that a lot of the information pertains to hydrophobic soil in agriculture.
Whilst the issue is the same, the solutions aren’t. Hydrophobic soil caused by extreme heat (that we don’t tend to get inside) is waaay worse and often needs chemical intervention. We don’t need to do that, so don’t go out and buy wetting agents – they’re unnecessary.
What is hydrophobic soil?
So, hydrophobic soil is basically soil that repels water.
Have you ever tried pouring water onto soil and noticed that it just beads up on top of the soil instead of soaking in? That’s a sign that the soil is hydrophobic.
It can be a problem because when water can’t penetrate the soil surface – and since water ALWAYS follows the path of least resistance; the water just runs off (usually into that gap between the soil and the pot).
This ultimately leads to moisture stress for plants (and all the accompanying problems, such as brown leaves). This is why it’s important to manage hydrophobic soils to ensure that water can penetrate the soil and reach plant roots.
There are a few ways to manage hydrophobic soils, including using wetting agents to help water penetrate the soil surface, mulching to reduce evaporation, and adding organic matter to the soil to improve its structure and water-holding capacity.
What causes hydrophobic soil?
There are a few different factors that can cause soil to become hydrophobic in house plants. One of the most common reasons is simply that the soil has become too dry.
When soil dries out, it can create a waxy coating on the surface of the soil particles. I’ve tried in vain to find out what this waxy coating is made up of, but Google has failed me.
HOWEVER what matters is that water molecules are VERY cliche-y. They love other water molecules, but HATE…everything else. Think of it as being a magnet (physicists everywhere are crying) – water molecules attract other water molecules but repel, er, other stuff.
This coating can repel water, making it difficult for the soil to absorb moisture.
So, if you forget to water your house plants for a while or if the air in your home is particularly dry, the soil in your plants can become hydrophobic.
Another common reason why soil can become hydrophobic in house plants is due to the buildup of certain types of organic matter. For example, if you use a lot of peat moss or other organic materials in your potting mix, these materials can break down over time and create a waxy coating on the surface of the soil particles. This coating can also repel water and make it difficult for the soil to absorb moisture.
Not only that, but some potting mix ingredients such as sphagnum and coir become EXTREMELY hydrophobic if left to dry out for too long.
Nothing short of soaking them in water will help which is fine for plants in pots, but can be a a massive PITA for moss poles.
Especially if your moss pole hydration regime is a little sporadic*.
*What a sentence! I’m proud of it, and Cher Horowitz would be too!
Will bottom watering help hydrophobic soil?
Bottom watering is the easiest way to rehydrate hydrophobic soil.
I just spent rather a long time trying to work out how this works, because surely if the wax repels it, then…we’re back to square one.
Also, if wetting the soil worked, wouldn’t farmers just do that after a drought? Also, rain will wet the soil?
And then I actually thought it (groundbreaking stuff, I know).
You can’t bottom water a field. Rain isn’t enough – it’ll just wash away, taking any non-hydrophobic soil with it. Aaaand when it’s super hot, then the rains tend to be aggressive and run off into rivers without penetrating the soil at all.
The waxy coating is only so water resistant. It won’t be a match for 24 hours sat in a bowl of water.
This was the issue I was having with learning about hydrophobic soil. Fields and pots need different approaches!
How long should I soak hydrophobic soil for?
One of the things that tripped me up when I first started getting into house plants was bottom watering. As an underwaterer, it’s often touted as the answer to my prayers, because it’s a great way to make sure the soil is thoroughly moistened, so it will therefore take longer to dry out.
When you read about how long to bottom water for, everyone’s like ’20 minutes is long enough!’
If the soil is hydrophobic, you may need to leave your plant in water all day. In summer (or at least, when it isn’t too cold), I might leave them overnight.
The reason we tend to discourage people from doing this kind of thing is that if you accidentally forget about the plant and leave it for a few days, then you could end up with root rot.
Bottom watering takes as long as it needs to. I sit my plants in until the pot feels heavy, or I root around in the top layer with the prong of my moisture meter until I see that the soil is holding water.
What can I add to make soil less hydrophobic?
Moss is not, because it gets SUPER hydrophobic:
this picture is from the top of my big Monstera. She’s currently bottom watering. It’s a big pot, and I just full the saucer until my moisture meter says it’s wet when I probe near the surface.
The moss on the top is probably never going to absorb water again. Capillary action is marvellous, but it’s unlikely to be strong enough to get all the way to the top of the pot.
If you have a similar pot, and you wish to hydrate the top of the pot, then you have a couple of options:
- Spray the top of the soil. This is especially good for those of us who like to spray stuff but know that misting isn’t necessarily great for plants.
- Bottom water in a pot bigger than the pot, and fill it up. I mean, it’s hardly bottom watering at this point – more straight soaking, but it does work (if you have a big enough container – this Monstera is bigger than a bucket). This is also a great hack if you want to bottom water quickly, because it’s not capillary action at play; rather it’s the water displacing air pockets in the soil.
Personally, I leave it be, and consider it the first line of defence against the relentless onslaught of fungus gnats.
Leca is also a great soil additive that, like perlite, aids in both retaining moisture and adding airflow.
A lot of people recommend adding organic matter like compost or mulch to stop soil from becoming hydrophobic but I cannot stress enough about how they’re usually referring to outdoor plants.
If you add compost or mulch to indoor plants you’re not only making your house plants look like the garden of Eden (minus the villainous serpents) to house plants BUT you can end up with too dense of a soil mix and end up with root rot.
A nice compromise here is to add worm castings to your soil. You can buy them from eBay, ro make your own wormery.
I actually have some worms in my bathroom monstera (the one that looks like – for good reason – it’s had thrips for years) and the soil is *chef’s kiss* and probably why the poor thing has an amazing root system and crispy leaves.
The worms just turned up. I assume there were eggs in the soil from…somewhere.
- Don’t let your plants dry out too much
- If you already have, soak the soil thoroughly to allow it to rehydrate
- Don’t use wetting agents – they’re designed for outdoor use and will end up ruining your plant and/or soil