Obviously, the type of hydroponic growing medium you'll choose depends on your crop, method, and purposes. To make that decision, however, you'll be comparing the characteristics of different types of media. Some terms can be pretty meaningless or confusing, especially when you make them into acronyms.
So here's your quick-and-dirty guide to media characteristics and how they can help you.
Specific Surface Area
SSA. Specific Surface Area tends to be overlooked, but is key to system health. It determines how aggressively you can feed, how quickly your system reacts to changes, and how resilient it is to pressure.
The reason that it can do so much for you isn't actually the surface area- it's what lives on it. Microbes! Billions and billions of microbes. You might be familiar with nitrosomonas and nitrobacter, but SSA houses hundred of other kinds of microbes involved in nitrification and mineralization. The more of them (and the more kinds of them) there are, the more robust your system is. Hands down the best thing that you can do for them is to provide them space to live and do their microbe thing.
Related to SSA is particle size. In general, the smaller the particle size, the more surface area there will be. Be careful, though! If you get too small, then you might have problems like clogging and anaerobic zones.
A tricky part about SSA is it's relationship with void space. Hydroponic growers benefit both from high void space (which creates aeration), as well as SSA, but when using aggregates, these two characteristics are inverse. Large aggregates have higher void space to volume but have lower SSA, and vice versa. If using fibers, however, void space and SSA can co-exist.
SSA is especially important to aquaponicists, who rely on microbes for every step of the nutrient cycle, from fish feed to plant available nutrients. In hydroponic systems, most of the nutrients that enter the system are already in their inorganic form, and can be taken up by plants immediately.
Cation Exchange Capacity (CEC)
You'll hear this term thrown around on forums and sometimes even videos about hydroponics, but it's actually not relevant to either hydroponic or aquaponic growers. Ignore it!
The importance of media weight can't be understated, because it's tied to ease of handling. Weight either limits your growing options or opens them up. Use a heavy medium, and you're left with one option; a stationary media bed. If you're planning on any other functionality, like the ability to clean your media, grow vertically, or move your growing apparatus, you're stuck.
We recommend using lightweight media and making it a priority when choosing a media.
Media usually comes either as an aggregate (like sand or gravel) or as a fiber (like coco coir or Matrix Media). Deciding which structure you want takes a bit of creative thinking. How do you wish to handle your media? If you'd like to be moving, removing, and planting your media as one piece, than an aggregate will be easier for you. If you're going to be planting and harvesting one plant at a time, then an aggregate might be better.
Media Structure Oasis Cell Plastic beads Aggregate Perlite Aggregate Vermiculite Aggregate Hydroton Aggregate Expanded shale Aggregate Crushed granite Aggregate Rock Wool Fiber Coco Coir Fiber Peat Fiber Matrix Media Fiber
Growing with aggregate medias can get pretty difficult if you're growing vertically. Many growers fill vertical columns with an aggregate and use it to house their plants. This makes it very difficult to replant the columns. In this case, the grower would benefit from using a one-piece media that they could pull in and out easily.
I'm not talking about certified Organic materials. I'm talking about whether your media is made from something that used to be alive, like coco coir, made from the husks for coconuts, or sawdust.
Having a lot of organic matter- even if it's primarily cellulose - will make a huge difference in your system's chemical and biological cycles. While some people operate very successful systems using organic matter as a medium, we think that you're better off using a mineral or synthetic material.
Why? Becuase if it's organic, it can - and will- be broken down. Most of the time you'll have trouble keeping oxygen levels high as that happens, and it will begin to rot, compact, and cause anaerobic zones. Not only is this just plain nasty (nasty looking, nasty smelling, nasty feeling), it will wreak havoc on your plant roots and cause disease problems.
Cost is simple right?
Well, kind of. And kind of not. You're probably thinking about the cost of the product that's listed on the online shop or on the shelf in your local hydroponics store, right? Well, that is important. But it's not all there is.
If the answer to any of the questions, "Is it reusable? Can I dispose of it easily? Is it safe? Is it sterile?" is no, then I have bad news for you. The buying cost is just the beginning!
If you have to replace your media after one or two uses, then you can multiply that buying cost, because you'll be doing that every couple months. (And cost isn't the only issue with one-use media, as you'll see below.)
If your media is something with potential health hazards (like perlite), then you better factor in the cost of the proper safety equipment, like masks and gloves.
If you use something that falls apart, then you better factor in the cost of the labor it will take to clean out your filters every day or week.
The point here is this: think about every possible cost. Not just the initial cost.
Hidden characteristics: biodegradability, handling, and health notes
There are some really crazy media being used out there. A lot of media are manufactured or sourced in interesting ways and made from interesting materials. This means that they have some unique characteristics that require unique handling, disposal, etc. Here are some issues to keep in mind when dealing with alternative media types.
Reusability and disposability. If your media is not reusable, you'll be disposing of it. Check out how the media is sourced and disposed of. Are there environmental concerns?
Health and safety. Some medias, like perlite, can cause health problems if handled incorrectly. Others impact GAP certification due to safety concerns. Before deciding on a certain media, it's worth a quick internet search to see if using the media has caused any complications for other hydroponic growers.
Sourcing. Some medias are made from non-renewable resources. This becomes an especially big concern when a media is also non-reusable. This means that every use of the media is a one-time use. Sometimes this is just not ethical.
pH. Not all media are created neutral. Some media, like peat or rockwool, have lower or higher pH values that can affect the pH of your solution. Others, like those made from limestone, may contain carbonates that buffer pH.
Hydroponic Media Providers
Hort Americas offers aselection of different media as well as help selecting the right one for your operation.
Hydrofarm also sells hydroponic media.
For raft growers, Bigelow Brook Farm's GrowGrips™ are worth checking out.
You can find Matrix Media here.
In conclusion, here is what we think makes the perfect media.
For most growers, the perfect media will possess these traits:
Good aeration and drainage
Good structural integrity
When we first started growing, we had a hard time finding a media that would serve farmers well and for a long time, so we created our own. Matrix Media is designed to make vertical farming easier and more rewarding for farmers.