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In general, it’s not necessary to put rocks in the bottom of plant pots.
One rock to cover the drainage hole is enough – just enough so that the soil doesn’t leach out of the bottom but water can flow freely out of the pot.
Putting rocks in plant pots doesn’t aid drainage or improve air circulation.
I’m softened my stance on this over the years. It’s not wrong to put gravel in the bottom of pots, and plenty of people do it.
However, adding gravel instead of drainage holes will do NOTHING to increase drainage and you're WAY more likely to get root rot unless you're very careful about watering veeeeery slowly and giving the exact right amount of water.
I do NOT have time for that.
There are, however, sometimes instances when putting rocks in the bottom of your plant pot are useful.
Instances when rocks in plant pots can be useful
1. When the pot is too big.
Rocks are cheap (free if you take them from the garden/drive), especially in comparison to the potting mix.
It makes sense to fill the pot to a certain level with rocks, just to save a bit of cash.
Do bear in mind that rocks are far heavier than soil, so prepare to have to leave your plant where you potted it if you find it’s too heavy to carry.
I sometimes use leca, because it retains water but dries out quickly and allows for great airflow.
This is especially useful when you’re potting up propagations, and you don’t have a small enough pot.
2. When your pot doesn’t have drainage holes
One thing you’ll know about me if you’ve spent much time in these parts is that I’m reeeeally passionate about drainage holes.
Just read this post if you don’t believe me.
Yup, I really wrote a 1,500-word article presenting my case about pots with holes.
I promise it’s not as dull as you’d think.
If you have no option other than to plant a plant in a pot without holes, you could put a layer of gravel on the bottom to catch any excess water and stop it from being reabsorbed by the roots of the plant.
You need to wait until any water is gone before rewatering, which is why leca is a better option than gravel – it can absorb the water and the soil can use it.
You’re still better off putting the plant in a nursery pot though – it’s just easier.
3. When you live somewhere windy OR your plant tends to fall over
Genius tip from the comments here. It doesn’t matter if you put the rocks at the bottom of the pot or on top of the soil, the principle is the same: a heavy pot is less likely to blow over/away.
As long as you have drainage holes in the pot, the water won’t collect in the bottom.
This is especially useful if you put your houseplants outside in summer.
Doesn’t putting rocks in plant pots aid drainage?
As I already mentioned, you just need one rock, to keep the potting medium in the pot.
The most important thing is that when we water our plants, the water can drain away. Not into the bottom of the pot, where it’ll go stagnant, and will rise over time the more you water. Out of the pot.
If you worry about wasting water, you can water over a pot:
Putting gravel in the bottom of a plant pot doesn't make the water drain away more quickly, it instead creates a perched water table.
What is a perched water table?
When you water a plant, there’s the saturated zone of the soil, and the unsaturated zone.
The saturated zone is at the bottom and the unsaturated zone is at the top because gravity causes the water to head down through the soil.
Everyone still with me?
Here’s a diagram:
The myth re. gravel and drainage came about because it was assumed that gravity would pull the water through the saturated zone and into the gravel, away from the roots of the plant.
As it turns out, that’s not quite how it works.
The forces that hold the water into the soil are stronger than gravity, so the soil holds onto the water - imagine laying a sponge full of water on some gravel. The gravel won't soak up the water - the sponge is holding onto it too tightly (source).
By adding a layer of gravel, all we’ve done is shifted the saturated zone closer to the roots of the plant.
If we water a lot, the gravel area will fill up with water and the saturated zone will turn to mud. ven if this doesn’t happen on the first watering, over time the layer of watr in the bottom will build up.
Soil that stays saturated for too long will cause root rot.
But don’t the rocks in the pot allow for better air circulation?
The water in the saturated zone is filling every air pocket with water, so the air can’t circulate from the bottom up.
If you’re worried about air circulation, then stab your soil a few times with something thin and pointy (chopstick, moisture probe). Should the soil be really compacted, your best option might be to repot the plant entirely.
You could also add soil amendments to make your soil chunkier – that will add drainage.
If there are no rocks in the bottom of my pot, how do I stop the soil from washing away?
You could line the bottom of the pot with some kitchen towel, newspaper, or even a bit of coffee filter paper. That’ll be porous enough to allow the water to drain away (or soak through, if you’re bottom watering).
To be honest, small layer of gravel here is fine, but as well as drainage holes, not instead of.
How do I increase drainage in soil?
We’ve already established that putting a layer of gravel in your pot won’t help the water drain quicker – it’ll hinder it in fact.
It’s all about the potting mix. I have a whole post on potting mix here.
You can absolutely make do with regular house plant potting mix, but always add perlite and orchid bark for more drainage. Perlite absorbs water, so the mix dries out quickly, but so not so quickly that you have to water your plants every day.
I have a Monstera-specific article on increasing drainage here, but it’s applicable to loads of houseplant species.
Add builders sand if you’re making succulent mix.
As long as you’re allowing your plants to dry out completely before watering them again, they’ll be fine. How completely they dry out depends on the plant, which is why I’m so in love with moisture meters.
I’ve already put rocks in my pots, should I repot?
Once upon a time I would have been like ‘YES. IMMEDIATELY’.
But now I look at it on more of a plant by plant basis.
Is your plant healthy? Does it get plenty of light? Is it growing well?
If the answer to all those questions is yes, then I would leave it be.
Plant vary a LOT even within the same species, and some are more resilient than others.
Also, LOADS of people keep their plants in pots with gravel at the bottom instead of holes with zero repercussions. It’s not impossible, I just think it’s more difficult for beginners.
Final thoughts on rocks in pots
I think I’ve made my stance here pretty clear, no?
- Don’t put rocks in your pot. Not only does it not aid in drainage, but it can also accelerate root rot.
- If you have a big pot you’re allowed a couple of rocks to cover the drainage hole so that don’t lose half the soil when you water
- But you can use kitchen roll or similar if you have a tiny pot (say, for one of those teeny tiny cacti)
And that’s it. Happy planting!