Grow Media
By Hydro Harvest
- 20 February 2025
Look at it this way. Your nutrients, your feeding regime, your watering system, your utilities, even your growing space can all be affected by one thing – your choice of grow media.
So, choosing a grow media is a pretty big deal. It’s definitely a good idea to understand what each type has to offer and what your choice means for your wider setup.
Here we look at the principal, commercially available types of grow media. Who they’re good for, what they offer, and what you’ll need to succeed with them.
Many of these grow media are commonly, and successfully, combined with each other to get the best of both worlds. In each case we’ve noted classic combinations. But it doesn’t end there.
Because growers are naturally curious and good at innovating, you’ll find any number of people out there cultivating with ‘improvised’ grow media. It’s hard for us to offer any solid advice on such ‘alternative’ media. But a chat with your fellow growers or even a quick google will reveal many interesting new dimensions in potting materials. Back to solid ground.
Soil
What is it?
It should be noted that we’re not talking about ‘down-the-park’ soil here. Specialist soils produced specifically with indoor growers in mind are what you’re after. Natural for sure but also clear of anything that could potentially harm your plants.
Who’s it good for?
The simplicity of soil might suggest it’s a bit of a beginner’s media. And it is true that many of the qualities of soil do make it a great choice for novice growers. It’s instinctive to use, reliable, and is easily combined with hand watering. But soil can be so much more than that if you want it to be.
What can you do with it?
Because it’s an organic material you can use soil to cultivate bio activity in the rootzone of your plants. Any number of beneficial fungi and bacteria can be added to create a fantastically healthy, growth-stimulating, and productive rhizosphere.
How do you use it?
Needless to say, ‘in a pot’. The type of pot you use may depend on your cultivation system of choice (see below), but you will want something with holes in the base for drainage and/or uptake of water.
Be aware that soil can get very heavy when wet and that your plant will only add to that heft. So, you’ll want a pot that’s sturdy and ideally from an indoor growing specialist.
Plastic pots are by no means the only choice for a soil grower. Equally you can choose fabric pots which offer extra aeration to the rootzone via their porous pot sides. Such containers also help to train your plant roots into uptake-optimised structures which typically produce bigger, faster growing plants from smaller pots.
Potting up
If you’re going with a soil based potting media, then rooting plugs are an ideal choice for propagation. Placed in a pot a rooting plug will seamlessly become part of a soil-based media.
When it comes to media for growth and bloom there are plenty of easily available choices out there. Many specialist soils come ready ‘charged’ with a dose of fertiliser that will see you through the first 4-6 weeks. This is excellent news for a couple of reasons.
Firstly, during those 4-6 weeks, you may only need to supply plain water to your plants. This makes soil a fuss-free, cost-effective choice. You don’t necessarily have to buy, mix up, or administer nutrient solutions for early stages.
Secondly, no one knows their soil like a soil producer. Provided your brand is quality you can be pretty sure that the charge of feed in the soil is a perfect match for the soil itself.
One issue with soil is compacting. When it gets very wet it can cease to function as a ‘wick’ to draw moisture up from your tray beneath or down from your supply above. This is why many soil growers opt for a mix with coco coir, clay pebbles, perlite, or vermiculite. Such materials improve aeration, ’drainage’, and maintain water retention. It is a bit of an odd calculus (holding whilst releasing) but it really does work.
System suitability
Because soil is a loose material any watering system you choose will have to work with an enclosed pot or container. This means drippers, automated pot-and-tray modules, or hand watering.
Drippers are inexpensive and reasonably fuss free. But beyond scheduling your pumps to switch on/off they don’t really consider the plants actual needs at any given time. Hand watering is incredibly inexpensive but time consuming.
Pot-and-tray modules such as AutoPot watering systems cost a little more to set up but feed and water your plants with no need for electricity or mains water. They’re automatic, saving on manual labour, and work 100% responsively – supplying in accordance with your plant’s requirements.
Coco
What is it?
Ground down coconut husks have been a best-kept secret of indoor growers for years. Commonly known as coir, this stiff is seriously versatile as a grow media.
Who is it good for?
Like soil, coco coir is natural, easy-to-use, and goes well in simple, low-cost watering systems. However, coir can hold much more water than soil before it saturates, meaning that in theory you can go longer between watering.
Coir also drains better than soil (making it more reliably functional as a ‘wick’) and is better aerated. This structural feature gives your roots a more oxygenated, ‘open’ space in which to explore.
Finally, with virtually no built-in nutrient content, coir gives you the opportunity to completely govern what you feed your plants.
The trade-off is that coir has certain characteristics that require some understanding and management. Because of this it is probably best suited to growers with a few harvests under their belts.
What can you do with it?
Broadly speaking, anything you can do with soil, and some. Coco offers you the chance to cultivate an aerated, bio active rootzone on entirely your own terms. You will need to ensure that the variety you choose is of decent quality though and is properly buffered. Any big brand from a specialist retailer should tick these boxes.
How do you use it?
Typically, coco is used in much the same way as soil. You need a sturdy plastic pot with holes in the base or a fabric pot. If you’re using an automatic watering system, such as AutoPot then your pot comes as part of the package.
Potting up
For propagation you can use coco-based plugs, blocks, or simply use coir ‘loose’ in seed trays and small pots – as you might with soil. As it drains well, wicks well, and offers natural resistance to molds and pathogens coco is really quite a good choice for young plants.
For growth and bloom stage plants coco is best suited to container growing. You can use it on it’s own or mix it with other grow media to optimise water retention, aeration, and drainage. Many industry leaders offer such blends off-the-shelf.
Because coco has no built-in nutrient content, you’ll need to be supplying a suitable feed as soon as your plants are ready for it. The good news is that coco-specific feeds are readily available, easy-to-use, and no more expensive than their soil equivalents.
System suitability
All the cultivation systems that work with soil will work equally well, if not better, with coco. You can go longer between hand watering, drippers distribute more fully, and AutoPots wick more completely.
Coco Management
As we’ve mentioned there are a couple of things to understand and manage with coir. Largely these have to do with pH levels and ‘draw’.
With coco desirable pH levels will typically be slightly lower than with soil to promote proper nutrient absorption. This requires a little management. On top of that coco has a habit of retaining or ‘drawing’ certain minerals and not passing them on to your plants. These minerals include calcium and nitrogen – essential for growth and development. Coco-specific feeds do compensate for these quirks in the media, but it is as well to keep one eye on deficiencies and one hand on a bottle of CalMag supplement.
Hydro
What is it?
Typically, a grow media that has no nutrient content, is pH neutral, and is otherwise unreactive. In other words, ‘inert’. Good examples include rockwool or clay pebbles.
Such media are often produced from natural materials but are ultimately man-made. Rockwool is super-heated rock spun into structures. Clay pebbles are expanded little baked balls of clay.
Who’s is it good for?
Hydro grow media are all about open structure and support. They give your plants something to grip onto and to develop in whilst exposing the roots to the regular or constant presence of water and nutrient solution.
In the case of rockwool this means a block of fibres with a vast number of little crevices. When you pour clay pebbles into a mesh pot you get the same effect – with a lot of little gaps between the individual balls.
Such media have little to do with actively carrying water or nutrients to your plants or cultivating an insulated, bioactive rootzone. However, combined with certain cultivation systems they do produce phenomenal results in very short spaces of time.
What can you do with it?
Because hydro grow media are inert you have complete control over your feeding regime. You do not need to wait for nature to take it’s course as you do with soil. Unlike coco, management of the media is minimal.
Most importantly though, you can use hydro media in the type of powered cultivation systems that supercharge growth and yield.
How do you use it?
Depending on your choice of media you’ll either use it in a mesh pot or with roots situated in blocks and combined with your hydroponic system. The whole point is to allow the rootzone complete access to moisture and nutrients so it’s unlikely you’ll be using an enclosed pot.
Potting up
Rockwool options exist for all stages of growth in including propagation. This makes it very easy to transfer your young plants from trays of propagation cubes into progressively larger blocks. Alternatively, you can propagate media-free with an aeroponic propagator.
Whatever stage of growth you’re catering for, a little bit of preparation is required in terms of pH adjustment for both rockwool and clay pebbles. This involves soaking them in pH adjusted water to get their pH to between 5.5 and 6.5. Once soaked rockwool may need shaking out but never wringing out – that’d destroy the structure.
How you pot up for a system depends upon your system type. Broadly speaking it’ll either involve mesh pots or blocks placed in / on a system tray.
System suitability
If you’re using hydro media, you’ll most likely have already chosen to grow with a DWC, NFT, or bubbler cultivation system. You can use rockwool with drippers, but this is a less high-impact technique.
Because DWC, NFT, and bubbler systems are heavy on utilities you’ll need ready access to power and mains water. Needless to say, you’ll also need a grow room that is big enough to house your system and any back up kit required.
All growing spaces need appliances to create the right climatic conditions. But, given the number of variables, this is doubly true of grow spaces that involve hydro-grown plants. Roots in hydro systems are uninsulated by coco or soil so may require more supporting warmth. On the other hand, the systems themselves may kick off more heat, so you need to balance that out.
More than anything, you’re already going to a fair bit of expense to get this crop fast and heavy. So, you really do want to make sure your environment is spot on. Therefore, you need space for the right kit.
Hydro Management
Hydro system management is not directly relevant to the subject of grow media. But if you are tempted by using hydro media in a hydro system you should be aware that such cultivation techniques require experience. You need to be attentive, always keep one eye on levels, and have a good understanding of what to do in the event of problems.
In Conclusion
Basic options with masses of scope, natural choices with remarkable qualities, advanced materials for staggering results. There’s so much to enjoy from different types of grow media. That is the genius of the stuff these days. Whatever you choose there’s plenty of fun and success to be had. True it takes a bit of forward planning, but that can be a really exciting way to re-engage your growing brain and imagine the possibilities.