Everything you need to know about growing in stone wool

You’ve probably heard about growers using stone wool for propagation or as an alternative to other media in their grows. If you’re looking to start using stone wool yourself, but you’re not sure how it’s used, or why to choose it over other products, then you’ve come to the right place. In this short read, we’ll explain how stone wool can improve your grow, and look at the main benefits of one of the market-leading products — Cultiwool.

What is stone wool?

Stone wool is basically a wool-like substrate made from melting down rocks such as basalt and anorthosite and spinning it into fine fibres – producing a material with the texture of dense candy floss.

What is stone wool

It’s used for a range of purposes, including soundproofing, fire protection and building insulation. You’ll sometimes hear growers refer to it as Rockwool, although that’s actually a brand of stone wool designed for insulation.

Horticultural stone wool is produced especially for growing, with a slightly different manufacturing process compared to industrial types. It’s the chosen media for the cultivation of medicinal cannabis, and also widely used in commercial agriculture — many of the vegetables on your supermarket shelves will have started out growing in a stone wool substrate.  And it’s just as useful a product for smaller-scale grows. 

 

Why does stone wool work so well as a substrate?

The textile-like structure of stone wool allows it to retain a substantial amount of water within its fibres, but drain off any excess water quickly. And as it’s inorganic, it maintains its absorbance and drainage qualities almost indefinitely.

That means there is constantly water in the substrate but never too much. This unique property gives your plants’ roots instant access to water while still allowing sufficient oxygen to circulate — through the air pockets. This balance ensures a consistent and even grow.

Why does stone wool work so well as a substrate

Compared to coco mix and soil, stone wool has the important advantage of being man-made, which means no risk of importing disease or pests with your substrate. Plus, it’s lower volume, and lighter weight, which makes it easier to work with from a practical point of view.

Stone wool doesn’t lock-up any nutrients, nor does it release any other unwanted substances into the nutrient solution.


What is Cultiwool?

Cultiwool is a brand of stone wool products developed to cater specifically for the hydroponics and medicinal cannabis industry.

What is Cultiwool

The types of plants grown in hydro systems require two important factors in a substrate — uniformity and hygiene. Cultiwool provides both. The unique manufacturing process creates the perfect density and orientation of the rock fibres — holding an ideal amount of moisture while also providing the porosity needed to ensure air circulation within the blocks. And as an industrially produced artificial substrate, Cultiwool is naturally pest and disease free out of the box.

 

Propagation in stone wool

Stone wool is a popular choice for propagation as it provides the ideal conditions for getting early root growth started.

If you’re growing from seed, your best choice is Cultiwool CRB plugs. You can simply place the seed into the plug, water it, and with the right conditions, you’ll see plants starting to sprout after just a few days. Once the seedling has grown to about 2 or 3 inches you can transplant it to a Cultiwool 3” or 4” block, an X-fibre slab or straight into the soil.

Propagation in stone wool

Cultiwool plugs are sized to fit perfectly into each other, so you can just drop a smaller plug directly into the holes in a cube the next size up — which means there’s no root disturbance.

If you’re working with cuttings, the process is slightly different. The best way to propagate these is to start off with a Cultiwool CRB plug, cut the plug in half, place the node of the cutting in the plug, hold the plug together and place it into a larger 3 or 4“ block — and then water it.

 

Growing in stone wool

Once your 3” or 4” inch block is well-rooted you can move on to the next stage. If you’re growing in an NFT you’ll probably want to leave your seedlings in the CRB plugs. With other systems, like a dripper, you might want to drop the plugs into a Huge block, Big Daddy block or even the X-Fibre slabs.

 

Using Cultiwool in systems

NFT systems like the Gro-Tank and Multi-Duct are ideal to use with stone wool. You can cut the top plate to fit the size of your block — ensuring it keeps out the light and prevents algae from forming on the cube.

Using Cultiwool in systems

Alternatively, if you want to grow in a slab then the Origin Duo slab is ideal. It’s custom-built to house the Cultiwool X-Fibre slabs, and the drippers then feed the nutrient solution directly into the slab.

For an Autodrain or Origin system, Big Daddy blocks are ideal. And the 1cm Cultiwool mini-cubes can be used with any drip-fed or hand-watered system — simply add them to the pot like any other type of media.

 

Growers’ tips

If you’re ready to get started with stone wool, here are a few tips from our in-house team of horticultural experts to help you get the best results.

 

  • Soak your blocks in nutrient solution (not water) prior to use. This stops them drying out. To ensure your block is fully soaked you can weight it – see soaked weights table.

  • Stay safe: Stone wool can cause irritation and even damage to your skin, eyes and lungs. To prevent this it’s best to wet the cubes before handling them, and we advise that you always wear a protective mask, goggles and gloves.

  • Keep the wrapper on: The wrapper helps to keep in the moisture, blocks out light to prevent algae growth, and also helps to divert root growth downwards.

  • Don’t worry about Algae on top of the block, this is normal and a healthy indication that plant has lots of access to water, oxygen and light.

X-stream Aeroponic Propagation

Propagating plants from cuttings is one of the quickest ways to build your crop — and as the plants have a shorter growth period compared to growing from seed, you’ll be able to harvest sooner. But there are a number of potential pitfalls you need to avoid to ensure your new plants thrive.   In this article, we’ll take a look at the key factors you should consider when propagating cuttings, and how using an aeroponic propagator like the X-Stream Aeroponic can give you the best chance of success. And as usual, we’ll finish with some top tips from our horticultural team to help ensure you get the best possible yield from your newly propagated plants. 

Foliar Feeding: How It Works & When to Use It

Plants don’t just absorb fertilisers through their roots—they can also absorb key nutrients directly through their foliage. For growers, knowing when and how to use foliar feeding is essential to protect the health of your plants, and maximise yields. In this article, we’ll break down some of the dos and don'ts of this type of feeding to help you get the most out of the technique.

Interview With House & Garden: The lowdown with Casey & Nate

We caught up with the product specialists to give us insight into House & Garden’s key products.