Selecting the right substrate for your hydroponic system is an important decision. Your growing substrate or medium is a core element of your farm. It takes up space. It costs money. It requires labor, and it supports, both biologically and physically, your main product—your crops. Choosing the correct substrate can make your job easier and more profitable. Choosing the wrong substrate can cause speed bumps and set-backs.

Hydroponic substrate selection is broad. They come both bound (one-piece) and as aggregates, as artificial or as natural media. They differ widely in particle and fiber size, amount of void space, percolation rate, weight, color, material and degradability.

Online forums, personal blogs and product manufacturers provide information on individual hydroponic substrates. While online information is piecemeal, some digging shows that information is abundant. The farmer’s decision is as easy as identifying what they need and matching it to the right product.

On second thought, maybe easy isn’t the best word. It can actually be quite difficult to solidify system needs. To help out, Tyler Baras (also known as Farmer Tyler from Hort Americas) and Chris Higgins lent their experience and knowledge on what it takes to choose the perfect hydroponic medium. Together we came up with these five pointers:

  1. Understand your technique.
  2. Ask the right questions about your process.
  3. Account for the unique needs of your process.
  4. Estimate external costs.
  5. Make a holistic decision.

Tip #1: Understand Your Technique

Just because a medium is great for one grower doesn’t mean it’s great for another. Each medium acts differently, which means that when you go to choose a medium, you need to know how you’ll be using it. Think through your system configuration, plumbing and main functions—all the things that define the technique that you use. Match that information about your technique to a medium.

For example, lightweight, low-density foam media and coco coir is best for contained units like trough systems, a media with a high-water-holding capacity such as stonewool is ideal if you can’t always be there to water your plants. Hosting your plant without a medium (usually aeroponics) requires a high level of precision and consistency in irrigation schedules, maintenance and climate controls.

Organic solutions often cause clogging, leaving plant roots to dry out. If you wish to operate a low-maintenance or organic system, bare-root is not the best technique. Also keep in mind that the different growth stages require different substrates, i.e., growing seedlings usually requires a different substrate than growing crops to maturity.

Tip #2: Ask the Right Questions About Your Process

Any prepared grower knows their growing and selling processes like the back of their hand. To understand how your growing, harvesting and selling processes will interact with a medium, you need to ask the right questions.

How does the medium respond to handling?

Two problems may arise if a medium doesn’t respond well to handling. The first is that it may crumble or fall apart. This can not only cause problems with irrigation and plumbing in the way of clogs, but it also changes the lifetime of the medium. Handling medium too often can also cause compaction. Compaction in many mediums changes water-holding capacity and may cause anaerobic zones or flow problems.

How will this medium work with automation?

Media need to fit into any automation process being used. If you’re using planting or harvesting automation, you will need media units that fit into the automation equipment. This could limit your options. Automation is often worth the limitation, but a cost/benefit analysis about automation equipment is always recommended.

Where is my growing medium going after harvest?

There are three core questions here:

  1. If you’re using a live sales model, ask yourself if your media is conducive to packaging and transport. If you plan on selling produce live to the consumer, then you must consider how it will be packaged and transported. Will it fit into the packaging? Will it be easy to transport and keep alive?
  2. Is this medium reusable and durable? If not reusable, media replacements can stack up and create a large cost. If it is reusable, will it perform well through its entire lifetime?
  3. Is disposal of this media ethical and easy? If your media is not reusable then it will probably end up in the trash. If you’re sending it home with customers, then most of it will probably end up in the trash. This could be an issue if the media is not biodegradable or if it is made from a non-renewable resource. Are you comfortable with that? Are your customers comfortable with it?

Tip #3: Account for the Needs of Your Application

By now you understand how your technique and your processes engage with the media you use. It’s time to consider application, the purpose of your media and the situation in which it will be used. Each application has unique needs.

For example, vertical hydroponics has unique requirements when it comes to a growing substrate. Compaction is a risk in vertical systems, so a vertical system requires a medium with good structure. Shear strength (essentially the force a material can withstand without it being torn) is also important to a vertical hydroponics application.

A strong medium allows the vertical farmer to handle it easily without risk of crushing, tearing, or wearing it down. This helps with labor costs and replacement costs. In addition to these two unique needs, vertical hydroponic growers should be looking for a substrate with good aeration. A synthetic fibrous media exemplifies these traits.

In another example, one form of live sales sends the produce home with the consumer still alive in a container such as a clamshell. This requires a substrate that is modular for individual packaging and disposable. An option that fulfills both of these needs is using no medium, like many DWC and raft producers. Individual plants—roots and all—are placed in packaging and kept moist until they reach the consumer, still alive. Since the consumer is also receiving part of the growing equipment with their produce, this application may also require that the media passes additional health and safety regulations.

One unique application of hydroponics is in the classroom. In this case, a grow medium would need to be easy to install and handle at every point of the growing cycle. Ideally such a system would be clean, neat and low-budget, and would make it easy for educators to show off plant anatomy. Each application has specific needs. What are your specific needs?

Tip #4: Estimate External Costs

Farmer Tyler says many growers fail to see that a substrate’s value is not solely its price. “Choosing an option that has the lowest price might be ignoring the external costs associated with using that product, like special germination requirements, additional labor and disposal,” he says. One example of special treatment is sterilization. Depending on where you get your media and what it is made of, it could require sterilization once before use or even as often as before every growing cycle. Sterilization may be chemical or physical. It could require special equipment and may affect your labor costs, timelines and processes.

Tip #5: Make a Holistic Decision

Once you’re familiar with the growing medium and how it will interact with your farm, combine all of your knowledge to make a decision. “A common mistake people make is focusing on just one factor (organic certification, price, size, etc.) when selecting a growing medium,” says Farmer Tyler. “Make a holistic decision based on irrigation strategies, certification objectives, germination conditions, automatization goals, crop size and price.” Creating a list of the pros and cons of each medium isn’t a bad idea here.

Once you’ve carefully thought through all the elements of your substrate decision, you’re set to make a good decision for your hydroponic system. Remember, a great substrate is only as strong as the equipment you are using. Pair your hydroponic media with smart farming methods.