Whether you’re looking for the easiest growing medium to work with or you simply want something safer to use for hydroponics that you don’t have to worry about being so careful with, these 20 rockwool alternatives include some of the best-growing medium choices currently available!
Hydroponic sponges are most commonly used for starting seeds destined for hydroponic growing systems.
Simply place your seeds inside, soak them in water, cover them, and stick them away from bright light.
After a few days, most seeds will be sprouted and ready for closer monitoring. They are also used as an alternative growing medium in hydroponic grow sites in place of rockwool.
- Lightweight and inert
- Fit to 1.8-inch net pots perfectly
- Nontoxic and eco friendly
- Works as seed starter and plant anchor
- Doesn’t fit larger net pots
LECA is quickly becoming one of the most popular rockwool alternatives on the market.
This growing medium consists of lightweight and expandable clay, making it perfect for rooting and supporting hydroponic plants of all sizes.
It isn’t the greatest for starting seedlings, but in tandem with hydroponic sponges or a seed starting system, LECA is as good as growing mediums for hydroponics get.
- Excellent water retention rate
- Long lasting and reusable
- Anchors mature plants (even the largest ones)
- Eco friendly and nontoxic
- 12-month warranty
- Is not ideal for starting seeds
- Doesn’t fit well with all types of hydroponic systems
3. Coco Coir
Coco coir, otherwise known as coconut fiber, comes from the husky of raw coconuts. The material is highly versatile and is highly favored by many gardeners and hydroponic growers.
This rockwool alternative is great for starting seeds and works well in netted pots too.
As far as growing mediums that work both for hydroponic and soil-based gardening are concerned, coco coir is one of the very best.
- Easy to use
- High moisture retention
- Works for starting seeds
- Provides structure for roots
- Is not always ideal by itself
For hydroponic bucket systems (such as Dutch buckets and DWC) and drip-type hydroponic systems (like NFT), few growing mediums are more suitable than perlite if you don’t prefer to work with rockwool.
The growing medium itself doesn’t hold any moisture whatsoever, which is why it works well only in hydroponic systems that keep the plant’s roots completely submerged or constantly and consistently wet.
- One of the most well-known growing mediums
- Works well in almost any type of hydroponic system
- Goes into most hydroponic and gardening mixes
- High water retention rate
- Works better as an ingredient in soilless mixes
Root Riot Plugs aren’t a type of product that are designed specifically for usage in hydroponics, but they do work well if you opt to give them a go.
These plugs are super-compacted sphagnum peat moss that can fit right into your grow sites and support fully mature plants in most hydroponic systems.
- Incredibly easy to use for beginners
- Starts seeds
- Supports plants
- Fits into most hydroponic grow sites
- It may require an additional growing medium to help anchor plants eventually
Soilless mixes are an excellent rockwool alternative for those who don’t want to put the effort into drilling holes and cutting cubes (or don’t have the time or tools to do so).
These growing medium mixes include everything from pebbles and sand to coco coir and perlite. They work well in just about any hydroponic system that uses net pots.
- Works in hydroponic net cups and in normal pots
- Has high water retention rates
- It may provide more natural trace nutrients
- Includes perlite and coco coir
- Isn’t specifically made for hydroponics, though it works well
7. Oasis Cubes
Technically, Oasis Cubes are plugs for seeds, seedlings, roots, and transplants. These specific cubes are inert and made from foam. They have zero impact on pH and are reusable.
The downside is that they may not be enough to support a fully mature plant without the help of an additional growing medium like LECA or a soilless mix.
- Works exactly how rockwool works
- Completely pH neutral
- Works well for starting seeds
- Supports mature plants
- It may require an additional medium to help anchor large plants
- Aren’t natural
Also known as bog moss, peat moss, and Quaker moss depending on where you’re from, sphagnum peat moss is one of nature’s greatest gifts to gardeners of both soil and hydroponics.
It consists of tons of dead material, making it completely organic. It’s also extremely good at absorbing and retaining moisture, making it a very ideal natural rockwool alternative for hydroponic operations.
- Works with hydroponics and soil/container gardening
- High water retention rates
- 99.8% organic sphagnum peat moss from Canada
- Great for starting seeds
- Isn’t an inert growing medium
- Works better when mixed with other ingredients (for hydroponics)
Vermiculite is not the most highly recommended growing medium for hydroponics because of the fact that it absorbs so much that it clogs systems.
That said, using it in a soilless mix or otherwise in small amounts along with an additional growing medium, like moss or coco coir, works as a great ingredient for rockwool alternatives.
- Has incredible water retention
- Affordable price
- Works well with coco coir, peat moss, and other mediums
- It’s recommended to mix vermiculite as an ingredient, rather than use it alone
10. Coco Coir Chips
This version of coco coir is another great rockwool alternative for hydroponic growing systems. The main difference is that chips are compacted and normal coco coir is light and fluffy.
At any rate, both forms work extremely well with hydroponics. Chips, however, aren’t as good for seed-starting as they are for supporting mature plants.
- Has all the same great properties as regular coco coir
- A compact version of coco fiber
- Good water retention
- Works well for anchoring tomatoes and peppers
- Doesn’t hold as much water as normal coco fiber
- Is not as ideal for starting seeds as it is for supporting plants in grow sites
11. Lava Rocks
Lava rock is another great rockwool alternative for hydroponic gardeners to use for growing/anchoring seedlings and mature plants.
The growing medium is extra lightweight yet has plenty of porous surface area (which provides superior drainage).
Furthermore, most lava rocks are pH neutral, making them even more ideal for use in hydroponic growing systems.
- Totally inert and pH neutral
- Superior drainage ability
- Works well for anchoring and supporting plants
- Long lasting and reusable
- Doesn’t have a nutritional value
12. Coconut Fibers
Coconut fiber offers up some of the most impressive oxygen and water retention rates out of all the alternative rockwool growing mediums.
The medium also provides plenty of firmness/structure for seedlings and mature plants to anchor themselves in grow sites.
It is important to note that it is one of the easiest growing mediums for new hydroponic gardeners to work with.
- Very high water retention
- Works great for starting seeds
- Supports seedlings
- Anchors larger plants
- Needs replaced more often than LECA or other inert options
13. Rice Hulls
Rice hulls aren’t used by themselves as often as they are used as an ingredient in growing mediums blends (soilless mixes).
Mostly, regular rice hulls are used as a replacement for perlite and vermiculite in hydroponic growing medium mixtures.
Rice hulls are also popular as a soil amendment for gardeners (that means you can use them in your potting mix and garden as well as your hydroponics).
- Works well as a replacement for vermiculite or perlite
- Mixes into soilless blends well
- Fits most net pots
- Can be used for hydroponics and regular soil gardening
- Does best when mixed into a blend
14. Hemp Fibers
Hemp fibers are another main ingredient in some organic, soilless growing-medium mixes.
These hemp fiber cubes, however, are a stand-alone product that easily replaces rockwool cubes.
They are safer to use, more cost-efficient, and easier to work with than rockwool in any form (sheet or cubes).
- Eco friendly and organic
- Works as a stand-alone solution for seedlings and plants
- Affordable price
- Very easy to use for beginners
- Additional mediums such as gravel help anchor larger plants
Pebbles and gravel, whether pea sized (basically fishtank pebbles) or slightly bigger gravel (like the kind used in landscaping), are among the most affordable and long-lasting hydroponic growing mediums.
However, both gravel and pebbles offer absolutely zero water retention, albeit they allow for great airflow.
Because they don’t absorb any moisture, they work best for simply anchoring plants in place in systems where the roots are in water all the time (like DWC buckets).
Pebbles and gravel are also great to mix with LECA or lava rocks.
- Cheap and easy to find
- Works well in DWC, RDWC, and other water culture systems
- Completely inert and pH neutral
- Long lasting, easy to clean, and reusable
- No nutritional value
- Zero water retention (or close to it)
16. Grow Stones
Similar to lava rocks or gravel, these grow stones are made from 100% recycled glass. They enhance drainage of grow sites and increase airflow.
They also absorb moisture, unlike most organic gravel and pebbles. When it comes to eco-friendly and affordable rockwool alternatives, you may be hard-pressed to find a better one.
- 100% recycled glass
- Eco friendly
- High water retention
- Good oxygenation
- Affordable price
- Not ideal for starting seeds
17. Wood Shavings or Bark
Wood shaving and bark are rockwool alternative hydroponic gardening mediums that often get overlooked. They aren’t the most common choice, but in a pinch, they work as well as gravel or pebbles.
Bark and wood shavings offer moisture retention and structure to growing medium mixes.
In addition, wood shavings and bark are great filler/ingredients to use in soilless mixes that also include mediums like coco coir or sphagnum moss.
- Easy to find for free
- Works as well as more popular mediums
- Perfect addition to coco or moss blends
- Good water retention
- Works for seeds, seedlings, and plants
- Not ideal for anchoring larger plants
18. Pumice Stone
Regardless that it’s number 18 on our list, pumice stone could well be the best hydroponic growing medium for your system if you’re not using rockwool.
Pumice stone is inert, porous, and pH neutral. It’s a lot like fish tank gravel and works well for anchoring hydroponic plants into grow sites.
- Inert and pH neutral
- Easy to find
- Comes in various colors
- Fits well in most hydroponic grow sites
- Adds zero trace nutrients to the hydroponic cycle
Despite the fact that sand is one of the oldest natural hydroponic growing mediums in the world, it is rarely used in hydroponic systems (by itself).
Generally speaking, it’s too heavy when wet, and while it does have water retention, it’s not great and neither are its oxygenation rates.
However, it is sometimes used as a secondary or filler ingredient for soilless mixes that include peat, coco fiber, and other similar growing mediums.
- One of the oldest hydroponic growing mediums
- Works well in most hydroponic blends
- Holds water longer than soil or gravel
- Dries out quickly
- Has no nutritional value
Sawdust is one of the least popular choices out there, but, if you are dead set against growing mediums like rockwool, it does work in some cases.
The main drawback is that if you don’t use a proper type of wood, like pine, the sawdust is practically useless for hydroponics, as it lacks any moisture retention or oxygenation.
- Lightweight and affordable
- Decent water retention and oxygenation
- Is easy to find (even for free)
- Great for starting seeds
- It may be too light to anchor plants by itself
The list of rockwool alternatives that you can use for a hydroponic growing medium is a long one.
That said, the 20 choices listed above are the most tried-and-true options, so you should have no problem picking one that perfectly fits all of your hydroponic growing needs!