How (& Why)to Use Silica On Houseplants

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Silica is one of those house plant secrets, that a small group of hobbyists SWEAR by,and the rest of us just muddle along without.

I see a few posts discussing the use of silica in house plants on Facebook but I must admit, I tend to blank them out.

Not because I think it’s a waste of time, but because I struggle enough with remembering to take my own supplements (and I take one vegan multivitamin. One. Sporadically, because my brain hates me), never mind ones for my plants.

Still, my job is to provide you with information. Do with it what you please!

What’s the difference between silicon and silica?

Silicon and silica tend to be bandied about interchangeably in the house plant hobby, but they are different. Silicon is an element, and it’s abundant, second only to oxygen, and makes up about 28% of the earth’s crust.

Silica is the form in which it’s found, and it differs from, er, raw silicon because it’s bonded to a load of oxygen. These bonds are very difficult to break, which is why sand doesn’t dissolve in the sea!

This rather begs the question: if silica is insoluble in water, how are plants gonna absorb it?

Can plants absorb silica?

Yes, but not always – it depends on the form it’s found in. For example, sand and perlite are made of silicon, but it has no bioavailability to the plant, so the plant can’t reap the benefits.

There’s a whole paper all about the benefits of silica and how to make it more available to your plants here (it was actually pretty interesting, as scientific papers go). Orthosilicic acid is a liquid silica that is commonly sold as a soil additive that plants can absorb readily.

Diatomaceous earth is a common fungus gnat repellant, but it’s also a form of silica that can be absorbed by plants. It’s also probably the easiest way to get silica into your plants because it doesn’t need to be administered as often as orthosilicic acid.

What does silica do for plants?

Silica is beneficial in a number of ways, but basically, adding silica to your plants makes them stronger.

Silica:

  1. Strengthens cell walls
  2. Supports stronger defences, and builds resistance to pests
  3. Helps grow broader stems
  4. Broader stems can then support bigger leaves
  5. Reduces digestibility – it becomes too hard for pests to eat, so they go elsewhere
  6. Reduces the risk of abiotic shock (such as heat or drought shock)
  7. Can provide a barrier between nutrient buildup in the soil and the plant

Silica builds up the cell walls of the plant, and acts as armour. Pests can’t eat the plant, it’s less susceptible to burning, and its structure is stronger.

Can silica be used as fertiliser?

Silica can be added in much the same way as a fertiliser, but it doesn’t contain the nutrients required to feed a plant. For that, you need a fertiliser that contains nitrogen, potassium and phosphorus. I like to use a fertiliser that has full spectrum of micronutrients as well.

Adding diatomaceous earth as well as your regular fertiliser will ensure your plant is both well fed and strong.

There is ongoing research about the benefits of combining silica with fertilisers and it seems to be looking positive.

A cursory glance on Amazon seems to suggest that you can’t (yet) get a full-spectrum fertiliser that also contains silica, but if there’s still research going on about how to effectively use it with fertilisers, then it makes sense that there aren’t any combined products yet – we probably don’t know how well they work together.

I mean, my nutrient solution is in three separate parts that can’t be mixed together without water, so I might be asking a bit much to have one product that will do everything.

It’s also worth mentioning that research is being done into rice plants. A product that feeds a lot of the world. I don’t think they’ll be doing large-scale house plant research for a while yet. Nm.

The general rule is that you can add silica to your fertiliser water, but make sure you add your silica to your water, then wait 20 minutes before adding your nutrients, to make sure the silica is bonded with the water before you add your nutrients.

Can plants overdose on silica?

Too much silica can make plants brittle, which I guess makes sense. It’s not toxic to them though, so don’t worry unduly about it building up in the soil (assuming you’re applying it as you would fertiliser).

If you’re using diatomaceous earth, use a mask. It’s not good for your lungs at all, and it’s very, very fine, so float around a lot.

Is silica good for all plants?

Again, research is in the early stages, but it seems to be.

There are rumours that silica is good for keeping the white parts of variegation from browning. I’ve not tried this, but I can see how it would work – it makes the white parts stronger and they’re less likely to die off. Also, if the plant is stronger, you may get more variegation.

A lot of people caution again keeping variegated plants in bright light, as the white parts can burn, but my Thai Constellation is in a south-facing window with direct sun and the leaves aren’t browning at all. If acclimated properly, the light does more good than harm.

Is silica sustainable?

To answer this honestly, we don’t really know. It’s INCREDIBLY abundant, so at the moment, it’s more eco-friendly than most of its alternatives, especially since its alternatives tend to be microplastics.

It’s a bit like asking if sand is sustainable: when it’s gone it’s gone, but also…we have plenty.

How to use silica with house plants

As I said, I’m a little reticent to try adding silica to my house plants because, in short, it seems like a ballache.

HOWEVER

The fact that silica makes plants less attractive to pests (and makes them physically harder to eat) has really piqued my interest.

Also, this is my job. Do it properly, Caroline.

I don’t want to add silica into my fertiliser because it could cause nutrient lockout. When you do use silica with houseplants, experts recommend that you add your silica (use the dosage that the manufacturer recommends) and then wait 30 minutes before adding your fertiliser. This will improve the efficacy of the silica and reduce the chances of nutrient lockout.

There are a couple of options:

  1. Use as a foliar spray
  2. Add silicon to the water one time, nutrients the next.

Ideally, I’d use the foliar spray. Foliar sprays are great because they help to keep dust levels down.

Except I never remember to use them. Anything with a spray bottle (including moistening my moss poles) my brain can’t remember to do.

So I’ll probably end up watering it in.

Final thoughts

Silica is revered as a wonder product in a few house plant groups, but then, so is SuperThrive.

In reality, there are very few products that will boost your house plants by themselves. The (disappointing) truth is that house plant care requires balancing everything, and making sure your plant has EVERYTHING that it needs.

Silica will not replace:

  • A good watering regimen
  • Appropriate light
  • Decent humidity
  • Regular feeding

BUT if you make sure have all of these things in place, silica can only help. It can reduce your pests, help with support, and allow for larger growth. Seems worth try, doesn’t it?

I love how I start tonnes of articles with ‘I’ve never tried this, and never will’ and inevitably end up running out and buying it immediately after I hit publish. What a sheep comprehensive researcher.

Caroline Cocker

Caroline is the founder and writer (and plant keeper) of Planet Houseplant

2 thoughts on “How (& Why)to Use Silica On Houseplants”

  1. There is a newer product out that combines perlite and silica or diatomaceous earth. What are your thoughts on this? I am experimenting with but I wonder about this being a workaround for the nutrient lockout you commented about.

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