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Author: Danny Donello / Category: Article / Published: Jun-13-2019
Although growing hydroponically is soil-free, this doesn’t mean that there is nothing to support our plants. In most hydroponic systems, growers use different types of hydroponic growth media to help support their roots and maintain a good water/oxygen ratio. In this guide, I’ll give you a breakdown of the most popular types of hydroponic growth media.
Firstly, some of you just starting out might be wondering what “Growth Media” actually is? It’s essentially soil substitute (or substrate as it’s also known). As your plants’ nutrition will be derived from solution, not soil, the growth media we’re talking about is, in effect, just there to hold the plants in place (think Neo in the Matrix, after taking the red pill, waking up to find himself suspended in a strange liquid – or growth medium!).
Almost anything can simply hold your plants in place, from polystyrene to sand. But before you rush off and improvise with old pairs of socks and toenail clippings, know that your medium should also be inert, lightweight, water-retentive and porous; to allow oxygen and solution access to the plants’ roots with minimal interference. And in this edition we’ll be taking a closer look at some of the more popular growth media products out there in the market, with a particular focus on Coco Coir, Perlite, Rockwool and LECA (or clay balls). Why these four? Because they’re easily obtainable, simple to use and will service practically all your growing needs.
If you thought Coco Coir sounds like some drunken, ageing diva in Los Angeles, clinging to her fast-disappearing youth in an undignified manner … well you’d be right. That is exactly what Coco Coir sounds like. But it’s not what Coco Coir is.
Coco Coir has become increasingly popular in recent years. It’s inexpensive, highly absorbent and can be used many times. Its pH value fluctuates slightly which can aid the absorption of nutrients. It also has an excellent cation exchange capacity (i.e. its ability to hold and release the various elements and compounds in your nutrient solution). And if that wasn’t enough here are a couple of other juicy bonuses; it’s got roughly double the porosity of rockwool; and a water-holding capacity that’s greater that peat moss.
But nothing in life is perfect; For one, Coir has a habit of retaining oxygen – which can lead to increased microbial activity; bacteria and fungi are rather partial to a bit of coconut. This is a positive when the bacteria and fungi are friendly, but something of a drag when the unfriendly variety takes root. The other thing of note is that nitrogen can also get “caught” in coconut media,so extra nitrogen may be required for your growing solution. And while Coir is reusable, it does break down and has been known to cause drainage issues.
Made from volcanic glass, perlite is cooked at such high temperatures it puffs up like a depressed, ice-cream-gorging menopausal woman going through a break-up. Or more sensitively put – like popcorn. This process is called Fusionic Metamorphosis. The glass heating that is, not the ice-cream gorging.
Perlite is bone dry due to its hydrophobic qualities (it’s water-resistant), but the thousands of tiny bubbles in its structure allow a degree of water retention. It’s cheap, light, and can be used repeatedly. For the drinkers amongst you, perlite is also often used by brewers to filter beer. So if you ever start your own micro-brewery, you might want to keep those sacks of perlite handy.
On the flip side, the lightness of perlite causes it to “work” its way to the top of your soil substitute mix over time. If you’re offended by the sight of these little white pebbles popping up at the top of your mix, we commend not using it if you plan on keeping plants in the same container for more than six months. And if you use an “ebb and flow” system with your plants you’ll notice pieces tend to float away during the flooding cycle. For this reason it is good practice to mix perlite with a heavier media such as the aforementioned Coco Coir. It also has a very low cation exchange capacity, something else the coir can counterbalance.
Lightweight Expanded Clay Aggregate. Otherwise known as Clay Balls (Morph fans look away now). These are, well, ball of clay – cooked until they puff up like a thyroidal fat kid who’s just had his face stung by a wasp. Or more sensitively put – like popcorn. The result is a mountain of extremely light, highly porous, spherical objects that look like very stale Maltesers. They might even taste like very stale Maltesers but for God’s sake don’t try to find out. The drainage and aeration qualities are superb and they can be sterilized and used time and again. They’re also chemically inert so won’t affect pH levels. They don’t retain moisture as well as Coir or perlite though and are best used in conjunction with another product such as Coco Coir. Use as a base layer in an ebb and flow system, or in top-drip pots to cut out algae growth.
This is a man-made mineral-based fiber, tweaked to be conducive to hydroponic plant growth. A bit like fiberglass, this can be bought in two different forms – repellent or absorbent. You’ll need repellent the type. Rockwool is used in hydroponics on an industrial scale and is the choice of many large-scale, professional outfits – mainly because it’s relatively cheap, holds its structure, retains water well, and has little cation exchange capacity (allowing expert gardeners to control the release of certain nutrients).
Okay, you’ve seen what’s out there. Now it’s time to apply the right media with the right system. There are six main systems – “Wick”, “Water Culture” “Ebb & Flow” (a.k.a. “Flood & Drain”), “Drip”, “N.F.T” and “Aeroponics”. This is Beginners’ Area as we’ve already been at pains to point out, so we’ll scrap the last two systems as they’re best left to the experts. That and they don’t really use growth media. We’ll address them in detail when you’ve earned your stripes, soldier.
The simplest of all systems – only suitable for small plants. The grow tray sits atop a reservoir of solution. A wick (as candle), sucks up the solution into the tray. It’s a passive system because there are no moving parts. There’s no flow of water so you don’t have to worry about your media getting bashed about, but as the wicks’ absorption rate is slow you’ll want to use media with good retentive qualities.
A mix of Coir and perlite are just fine for this system. If you’re feeling adventurous whack in some vermiculite.
The type you see in classrooms. Cups of plants in Styrofoam, floating atop a tank of solution – again, only suitable for small plants. Very little growth medium is required as the roots should dangle directly into the solution. Water retentiveness is therefore not that vital.
A small amount of perlite to hold the plants in place will do the job.
A pump on a timer will flood your grow tray at intervals throughout the day. When the pump switches off the solution will then drain back into your reservoir. Because if the regular flow of solution you will find the growth media potentially moving or coming apart, so you’ll want to mix in a heavier medium like Coir.
This system also operates on a pump and timer basis; except the solution from your reservoir is released through a drip line to the base of your plants. There are two versions of this system – Recovery and Non-Recovery. Quite simply, the former will return excess solution to your reservoir; the latter won’t.
A 50/50 mix of perlite and Coir will again suffice, and some growers will recommend an inch of clay balls at the top of your mix to cut down on algae.