Rockwool is one of the best growing mediums for hydroponics.
It’s cheap, fibrous to provide root support, and holds on to a ton of water.
But not everyone wants to use what started life as an insulation material.
If you’re looking for some Rockwool alternatives for hydroponics, this is the list for you.
Read on for 14 other options to check out.
Affiliate Disclosure: In this article, we may link to some of these options on Amazon. If so, it’s safe to assume the link is an affiliate, which means we earn a small commission at no extra cost to you.
Table of Contents
Clay Pebbles Or Pellets
Clay pebbles are my favorite option outside of Rockwool.
I even use this in combination with Rockwool!
These expanded clay pellets (or pebbles) are also known as hydroton pellets.
These are baked clay pellets, and they come in a variety of sizes.
They’re cheap, support roots pretty well, and are made of all-natural materials.
The ball shape also allows for ample oxygen to get to the plant, making it dry out quicker.
When wet, these hydroton pellets get heavy, so make sure the container is up to holding the weight.
This medium works with any hydroponic method, but it excels with high-water systems like:
- Ebb and Flow
- Deep Water Culture
- Drip Systems
- Mason Jar Hydroponics (click link for our guide)
Perlite/Vermiculite
You’ll often see perlite and vermiculite used in combination.
These are both types of light volcanic rocks, and they’re often sold and used mixed.
Perlite isn’t great at holding onto water because it’s so porous. This helps it provide good aeration and oxygenation.
It’s also odorless, light, and sits in the ideal pH level of 6.0-7.0.
Perlite sort of looks like white popcorn (but don’t eat it! Ha!).
Vermiculite makes up the difference in almost every way.
It holds onto water extremely well and looks like little worms or flakes.
Experienced hydroponic gardeners will mix their own to reach the exact setup depending on the plant and system they use.
For example, a Dutch Bucket or Deep Water Culture won’t need a medium that holds onto a lot of water, so they’ll use more perlite.
But a Nutrient Film Technique or Wicks system may add more vermiculite to hold onto the less amount of water.
Speaking of Dutch Bucket, these rocky mixtures work best with this method, though it’s customizable to any method with some experimenting.
Potting Soil
One of the whole points of hydroponic growing is to use no soil, but the fact is, many people all use the systems because it enhances the growth rate of the plants.
Potting soil doesn’t contain many bacteria, and it will support the plants’ roots, aerate, and retain water.
But the roots will grow down through the soil in a net pot into water, creating a hybrid system.
The high-nutrient hydroponic water solution will still enhance the growth of the plants.
Don’t write potting soil out as an alternative to Rockwool if you’re OK with a hybrid system.
Speaking of Rockwool, if you do decide to use it, check out our guide for using Rockwool in hydroponics.
Gravel
Gravel may seem odd as a growing medium, but it works pretty well in a hydroponic system if done correctly.
It’s simple, supportive to the plant, available everywhere, and dirt cheap.
The chunky rocks provide good oxygenation, but it doesn’t hold water well at all.
So if you use this, you’ll need a system that provides a lot of nutrient-rich water often.
However, gravel is heavy, so make sure your system is up to it.
Gravel is reusable, too, giving it even more monetary value for those willing to make it work.
The biggest thing to watch for with gravel is making sure you sterilize it.
Debris with bacteria will quickly cause mold and algae to grow in your hydroponic water.
This may infect your roots, causing the plant to stop growing or even die.
Sure, it’s possible to trim roots in hydroponics, but it’s better to avoid the issue altogether.
Check out our guide for trimming roots in hydroponics.
Before using and in-between each plant you use it for, wash it well using water and then sterilize it with heat, steam, bleach, or hydrogen peroxide.
Pool Noodles
Pool noodles are an interesting option.
They provide support, aeration, and even retain water fairly well.
Trim them to fit the length of your plant.
You’ll often see these in Nutrient Film Technique systems where long lines of gutters with flowing water pulled into the roots through a capillary pad.
Pool noodles, in particular, work well with longer and taller plants; they may not do well with shorter, stubbier ones.
Gardening Soil
Gardening soil is popular because it works great for all types of…well…gardening.
Its soil is enriched with nutrients, it has a rich, airy texture for support and aeration, and it holds onto amazing amounts of water.
Of course, not all gardening soils are created equally, but most will do the job.
So, if you’re really in a pinch, use some soil to support the plant and let the roots dangle.
But at this point, you may as well just grow the plants in a regular soil pot.
Due to the water retention, you shouldn’t use it with any heavy water systems.
This means no Ebb and Flow, Deep Water Culture, Drip System, Kratky, and even the Nutrient Film Technique.
Also, the nutrients already in the soil will over-saturate if you mix your hydroponic solution with the same ratio.
In short, it’s an option, but not a great one.
Warning! If you do pick gardening soil, don’t use soil from your garden. This may be filled with extra bacteria or insect eggs.
Jigsaw Foams
Jigsaw foams are mats, often interlocking, used in nursery schools and some playgrounds.
You’re free to cut them up in whatever shape works best for your system and plant type.
Use cross shapes for seedlings or circles (like the pool noodles) for more grown plants.
Like the pool noodles, this foam is made of ethylene-vinyl acetate, a compound used in all sorts of things, including:
- Hot glue
- Floaties
- Baby teethers
- Costume parts
- Some adhesives
This particular compound is non-toxic and contains no BPAs, heavy metals, or chlorides.
Sand
Sand isn’t a great option all on its own.
It isn’t super supportive, doesn’t aerate well, and doesn’t hold a lot of water.
So why use it?
If you combine sand with some of the other mediums, it’ll end up doing the job well enough, and you’ll save on money and material for the other mediums.
Rice Hulls
In the rice milling process, the coating of the rice is peeled off. These are called rice hulls.
It’s a natural product, and it’s quite cheap.
It’s also biodegradable and great for the environment.
They hold water well (they were designed to help with that in rice, after all).
Rice hulls don’t clump up, so they let ample air seep through.
They have a slow decomposition rate, meaning you won’t need to replace them often, and they also don’t have a lot of natural nutrients left in them.
This won’t throw off your hydroponic solution mixture.
Most gardeners who use rice hulls mix and match with another medium of their choice.
Don’t ever use rice hulls that were stored uncovered outside. They pick up bacteria quickly and will cause problems.
While some rice hulls will stick around after one or two crop plantings, they will build up on the salts from hydroponics.
If left like this, the charge from the salt will prevent any roots from absorbing nutrients.
Oasis Cubes
Oasis cubes are foam specifically designed to help with growing. They have open cells for optimal aeration, water absorption, and root growth.
It’s made from phenolic foam, and commercial growers tend to use it for efficacy and usability.
Like Rockwool, Oasis Cubes make great seed starters.
They hold 40 times their weight in water and even have a wicking property that lets them draw nearby water into them.
They pretty much work perfectly for any hydroponic system.
They’re a better (and more expensive version) of Rockwool.
Pea Gravel
Pea gravel is everywhere and a versatile product.
On its own, it’s only good for helping hold the weight of the plant.
They won’t hold water at all.
Mixing pea gravel with cut-up oasis cubes, clay pebbles, or Rockwool is a must.
Also, make sure you clean and sanitize your pea gravel to prevent spreading bacteria.
Sawdust
I put this on the list because some people find success with it, notably with tomatoes, but it’s a little dangerous for most people.
There are too many variables in what is in the dust. It could kill the plant as much as help it.
If the wood was treated with chemicals, those chemicals would now be in the water and plant.
It functions similar to sand with higher water retention.
I’d skip this altogether, though.
Sphagnum Peat Moss
Here’s a natural and eco-friendly option to use as a growing medium.
Sphagnum peat moss is a good overall medium, and it’s readily available.
The spongey material is great for roots, holds a lot of water, and provides decent aeration.
For some reason, it gets overlooked a lot by hydroponic systems and gardeners.
We’ve only gotten into using this a little at a time in our systems, and it seems to work well so far.
Experts and users alike agree its only downside is how it breaks down quickly, and little pieces may flake off and get stuck in any tubes, pumps, or pipes.
So it may not be best for Ebb and Flow, Nutrient Film Techniques, or Aeroponics.
Check out our detailed comparison of Aeroponics vs. Hydroponics vs. Aquaponics.
Polyurethane Grow Slabs
In my research, I came across this polyurethane grow slabs which are specially made slabs with air and water pockets specifically for large-scale commercial growing.
These seem fairly new and aren’t available for the everyday gardener, so they’re not a feasible option.