In the original hydroponic system NFT [Nutrient Film Technique] you do not require hydroponic media as plants are planted in net pots and roots grow in channels where the thin film hydroponic nutrients run under the media. Similarly, in DWC [Deep Water Culture] or Kratky systems, the plants are in pots and roots dangle in water, and no hydroponic media is required. This is fine for lettuce and small herbs in small net pots. But any other plant [even Basil] needs hydroponic media to support the plant from toppling over. This is especially true if go to larger Net Pots and Dutch buckets or even Ebb-and-Flow Basins.
Hydroponic Media Types
A search of media types will give you various options so in point form here is types can think off now, in no particular order:
- Sawdust
- Gravel
- Expanded Clay Pellets [Leca]
- Vermiculite
- Peat Moss (Spagham)
- Coco Coir
- Perlite
- Volcanic Rock [Pumice]
- Sand
- Rockwool
- Oasis – Floral Foam
The Primary and really sole function of the hydroponic media is for plant support. Hydroponic Media is not there to retain water, nutrients, etc. In fact, you need a hydroponic media that can drain quickly and not be waterlogged.
The overall factor is cost as always. People stress on weight aspect but think this maybe because they got cheap systems that can barely support the weight of the water. So, when you decide upon media – you first need to decide what you want to grow? Lettuce, Peppers or Oak Trees – then you decide on the how, ie which hydroponic system. Read the blog on “Hydroponics inna nutshell” for system descriptions to get an idea of different types. But just as a quick recap here is an image showing the 6 main classes.
6 Classifications of Hydroponics
In NFT, DWC and Aeroponic systems you don’t use hydroponic media. This is also the systems used commercially for growing lettuce, rocket, parsley, – basically any small plant.
Wicking systems I also call ‘bottom feed’ and this is the ‘Soda Bottle’ system first made, can read more in Hydroponics 101.
Drip feeding, is also what I call “Dutch Buckets” – aka “Bato” Buckets. Ebb & Flow similar to Dutch buckets, but in Ebb and flow one big bed and pump never stops, whereas Dutch Buckets only pumped for while.
Dutch Bucket Hydroponic Media
Drip Feeding systems [aka Dutch/Bato Buckets] is the de facto system to use to grow from Spinach to Trees. In this image in the foreground is the Dutch bucket systems – made of 5L water bottles. The water bottles have holes in them 1″ from bottom and the trays collect water and return to reservoir.
In the Background is the ‘Soda- Bottle System’ – made of 2L Coke bottles. This is a wicking system, or as I call it ‘bottom feed’. The water flows through the interconnected bottles, underneath the pots containing hydroponic media, and wicked up. Because of the curvature of bottles don’t pump whole time [on same cycle as Dutch buckets], as will keep some water in neck of bottle. So can be considered hybrid Wick/NFT/DWC. Exciting times now of using this system to do real Organic Hydroponics!
And now am stuck as really do not know how to go further… Especially because experiments with Organic Hydroponics has turned things a little bit on head!
These two systems are poles apart. For the wicking system you want a hydroponic media that can help ‘suck up’/wick the water & nutrient, so inert material like LECA [Light Expanded Clay Aggregate], gravel, sand, etc will not work at first – until plant roots are in the water. Therefore for these hydroponic medias you require a ‘wick’ that will raise the nutrients through capillary action.
For the Drip systems you want hydroponic media only to support plant and not retain water as ia a ‘flow-through’ system, you pump in water in top and it exits bucket close to bottom [NOTE: not at bottom].
Cheapest Hydroponic Media
This will depend on where you are – but for years had grown with sawdust! Plain old pine sawdust, dirt cheap and maybe can even get a bakkie load for free. Grew for years on this with no problems, the only problem is that so light that the Chilli plants blew over! This rectified by throwing gravel, the real cement aggregate kind, in the bottom of the buckets to fill up the water retention zone. The other problem with sawdust is that is organic, and plants/bacteria/fungi will consume the media so may need to fill up buckets periodically.
Keep clear of Western Red Cedar, they contain anti-fungal and anti-bacterial volatiles, and will be eked out by the flowing water and definitely stunt growth and may even kill the fragile plants.
Which brings to other hydroponic media, gravel, like the 13-19mm cement mix type. Just first give a wash/rinse to remove fine grit and sand and good to go. Can be used ad nauseum, when finished with grow just throw in sun to dry then rinse off and fill next bucket. Of course, the main problem is weight! Five liters weighs close to 10 kilograms, so my Dutch Bucket trays would need to support 120 kg, before water and plants.
Sand is also an option [Note Sand, not Soil], but need to get bigger than 2mm – like the pool filter kind. This is not so cheap and from experiences clogs up pretty quickly in the drip feed/Dutch Bucket system, that is why wash the gravel.
Best Hydroponic Media
The hydroponic media used by commercial growers is Rockwool, this is almost like glass fiber [think Pink Aerolite!] but made from Basalt Rock and Slag. This is also the insulation they use on boilers/piping in the power station/industrial industry. Import item and very expensive main Con, but also because of manufacturing process got a high pH [think drain cleaner] so has to be put in a light acid bath for 24 hours. Though this is for the construction kind as mentioned above, for the hydroponic/agriculture kind they should be treated already? Think why commercial growers like rockwool is because nowadays you can buy quite a large block that wrapped in plastic on sides, so don’t need a container, makes for easy cultivation.
Floral Foam: Stay AWAY, learned the hard way this not for living plants – but as name says ‘floral arrangements’. Pity, as cheap… I put in list above as booby-trap, and saw it listed on some sites!?
LECA: The factory in Paarl shut down, so now all import, was R300 five years ago! But for me this is one of the best media – inert, lightweight, and reusable. For the Dutch Buckets can be used on own – and for the wicking system use with dash Vermiculite.
Local is Lekka
South Africa is the world’s largest producer of Vermiculite, so my heart will always be with it. Made from Mica in ovens, think heated to circa 800°C, and then the ingrained water literally explodes the Mica flake into a worm-like tube of platelets.
Pumice is naturally formed volcanic glass from when a volcano erupts at surface, also from Basalt [refer to Rockwool]. Lightweight and floats on water. Perlite is just the man-made version of Pumice, and made similar to Vermiculite in oven, then at 800°C the ingrained water explodes the liquid glass.
The difference is the material, perlite is glass and hard – vermiculite is Mica and soft. So perlite is used drier mix, like Cactus, and Vermiculite for a wetter mix like Ferns. Perlite cannot be used on own as so light with ingrained air will just float away on water.
Vermiculite retains water longer than Perlite, and because of this fact is great for seedlings, together with fact that pH neutral. A good Seedling mix is 70% Buffered Coco Coir 20% Vermiculite: 10% Vermicompost by volume. For years I could not source a properly buffered Coco Coir so used a 70% Vermiculite: 30% Vermicompost mix. This change when learnt how to buffer the Coco.
The Coco Coir and Peat Moss Hoax
This I think is the greatest CON of the hydroponic media world, Coco Coir is Sustainable and Peat Moss is not!?
Great swathes of the natural rain forest slash and burned in Nigeria to plant a non-indigenous plant, and goodness knows where else?
The U.S. gets up to 80% of sphagnum peat moss it uses from Canada. In Canada, the peat bog mass harvested each year is an estimated 1/60th of the mass that accumulates. About 0.02% of the 1.1 million km2 (422,000 square miles) of Canadian peat bog are used for peat moss mining.
So the TRUTH is that Sphagnum Peat Moss is sustainable. Coco Coir is a waste from man-made plantations, which in the very heart of things is not sustainable! Coco Coir is basically just the Coconut shell husk that needs to disposed of – and the easiest way to do this is to sell to gullible people?
Anyway – rant over. Just a quick note, maybe people are confused by the word ‘Peat’. This is a precursor of lignite [coal] and grows at only 1mm/year, definitely not sustainable, but is formed at the bottom of the bog so operations typically not close.
By using Coco Coir in our gardens we are though implementing one of the core tenets of sustainability and ‘Reusing’ a waste product. In the process we are also removing mountains of salt from Indonesia which would make them pretty infertile. Coco Coir has more salt in it [NaCl, or Sodium Chloride] than Biltong! For Biltong [or Jerky] you add 2% salt – Coco Coir contains 6%…
Buffering of Coco Coir.
Coconuts are coastal plants and have adapted to their environment, with a thick waterproof shell/husk, that protects the coconut seed from long exposures while floating on sea. They are naturally high in Sodium and Potassium – Coco Coir has more salt in it [NaCl, or Sodium Chloride] than Biltong!
Coco Coir is a great product, it just needs to buffered correctly, to remove the Sodium and Potassium and replace with Calcium. Refer to BioACt which was released for mushroom substrate pasteurisation, but has been found to be a great buffering agent for Coco Coir for hydroponics/soilless mixes too. Not only buffering the Coir – but also adding Calcium Sulphate, a soil amendment, and Starches to encourage microbial activity.
In an aqueous solution the Cations will flow [much like a battery, anode and cathode]. Fortunately for us both Sodium and Potassium have single covalent bonds, whereas Calcium has two. So the Calcium will replace the Sodium and Potassium in the Coco Coir. Contrary to belief this does not happen overnight, more like 3 days [72 hours] at ambient temperature.
BioACt also has another trick up sleeve, because of the Calcium Hydroxide, the pH will drop from start at 12. When the pH has returned to neutral, 7 – 7.3, then the buffering process complete – and this is 3 days on average. A quick rinse with water and EC will be below 300-400 μS/cm and ready to use.
You need an excess of water to properly accomplish this Cation Exchange process, found 20 litres per kilogram and half Coco Coir good. The drain effluent is high in salts [displaced Sodium and Potassium] dispose of this water in drain. After buffering and draining also advised to wash/flush the Coco, ie add a bucket of water to drain out and remove any residual salts in solution.
Unprocessed Coco Coir can have an EC of up to 6000 μS/cm. Bearing in mind that this mostly due to Sodium and Potassium, when you add your hydroponic nutrients then the Calcium and Magnesium from nutrient will be absorbed [Cation Exchange] and Sodium and Potassium released. The netto effect for the plant is that it will received no Calcium, a macro-nutrient, only Sodium…
