A close-up of peat-digging on Harris, Scotland
Photo: Adobe Stock

There have been a lot of advancements in growing media in the last few years. Growers who once only had to consider which peat-based product was best, now must choose from products containing peat, coir, perlite and recycled fibers. Some of these are also enhanced with mycorrhizae and other biological agents.

The only way to see if these advanced products are good for your growing operation is to trial them in your own greenhouse.

“The substrate industry is advancing in two areas. More sustainable resources and using natural and biological means to enhance crop growth,” says Charles Bethke, an independent horticultural consultant. Bethke believes that it’s important to keep up with the advances that are propelling the industry forward, or as he likes to quote: “When you’re green you grow, and when you’re ripe you rot.”

Another reason to trial media is if you’re growing a lot of different species of crops in your greenhouses.

“Today we have it where growers are trying to grow a little bit of everything,” says Peter Konjoian, president of Konjoian’s Floriculture Education Services. “Yes, we all want one mix for the entire operation, but if we’re trying to grow a variety of species, it’s not realistic. It’s like trying to put a square peg in a round hole.”

Trialing a new media or substrate

Like anything you do, it’s important to define your goals or mission.

“You have to ask the question, ‘Why trial a new growing media?’” Bethke says. “Are you looking for something better, to save money, be more environmentally responsible, longer shelf life, use less water and fertilizer?”

While trialing different growing media or substrates is the best way to find out if a product is suitable for your growing situation, Bethke says it’s important for growers to understand that when they switch to a different product the management of the crop will change.

“If you’ve used an old mix and are now trialing a new one you’re going to change your management of that crop,” he says. “For instance, if I say I don’t want to use a peat-based medium, then that changes the way you fertilize, the way you handle the product.” He adds that different substrate blends require different amounts of water and fertilizer, especially nitrogen. A bark blend will require more nitrogen and coconut coir more fertilizer, at least in the initial stages.

Before you start a trial with a new substrate, find out as much as you can about the product. Most manufacturers have spec sheets for their products and may have results from their own independent trials. You can also ask other growers what they think of the product. And of course, you can take a look at reviews and comments in forums on reputable internet sites.

Photo: Adobe Stock

Consider the variables

When you trial is important, according to Bethke. Results can differ from season to season as well as from one situation to another. There are many other variables to consider and they can differ from one greenhouse to another. They include things like light intensity, irrigation and fertilizer delivery, and even ventilation. Evaluating and recording these variables from the get-go will improve the accuracy of the trial.

The problem is a lot of times, growers get too busy with other things to keep accurate observations of the product they’re trialing.

“Keep track of what you’re doing,” Bethke advises. “Because, I’ll tell you what, everybody forgets. You’ve got a lot of things going on.”

To take it one step further, it is all about controlling the experiment.

“Control, control, control,” Konjoian says. “And there are different layers to that.” He says one layer is controlling the variables in your control group or mix that you are comparing it to.

Another layer of control involves the crop growing in the new mix. It is important to control and especially record crop input variables including water, ventilation and fertilizer.

“If a grower says they usually grow hanging baskets above a crop and water drips into the trial plants, then you’ve introduced experimental error,” Konjoian says.


Designate an area for the trial

For some growers, designating an area to trial a new media could be difficult. Who wants to give up precious real estate during the spring growing and shipping season? Bethke says the answer is to find the smallest management area you can observe. In other words, you don’t need to use up too much space for trialing a substrate. The important thing is to locate it in an area that is easily observed from the walkways in a greenhouse.   

Konjoian adds that the size of the trial and how you want to set it up in your greenhouse will largely depend on the size of your operation and other considerations, such as automated vs. hand watering. The important thing is to try to control the variables of the control and trial group as best you can and keep meticulous records.  

“You may need a larger sampling if there are a lot of variables,” Konjoian says, referring to things like ventilation and the “border effect” of plants growing along the edges that receive more light than those in the middle.

Conducting a growing medium trial

To conduct any type of meaningful trial or scientific inquiry, for that matter, requires a control group. So it’s important to not only record the growing methods for the test group, but also the control group. Considering the variables mentioned above, growers can experiment with a number of things: well water vs. treated water, different rates of fertilizer application, plant growth regulators vs. no spray, etc.

Before you’re going to switch an entire growing operation, or even a portion of it, over to a new growing medium, it is important to replicate the results of your trials. This can be done in a couple of different ways. One would be to simply grow another crop of the same plants under the same conditions (and season) and see if you get the same results as previously recorded. The other way is to use the “rule of three,” where you trial three or more plants under the same growing conditions and compare the results to each other. The ultimate goal is to have confidence the new growing media will work for you before growing the entire crop with the new substrate.

A stack of coconut coir
Photo: Adobe Stock

Don’t fail to plan

One adage Bethke didn’t mention was the old one that says, “Failing to plan is planning to fail.” Changes are coming to the industry when it comes to choices for growing medium, with a lot of emphasis on products that are environmentally friendly. Growers may wish to stay ahead of the curve on these changes and advancements, particularly if and when consumers demand growers use recycled and other sustainable mixes.

“This year the largest amount of information provided at the Mulch and Soil Council conference was about recycled substrates and environmental concerns.” Bethke says. He adds that although there is an abundance of peat moss in the bogs in northern Canada, there is still the perception from consumers that the bogs are shrinking, which in fact they are in Europe.  

As a final note, Bethke says many growers are looking for the least expensive growing media to use in their operations. However, you don’t save much if that growing medium doesn’t hold water or fertilizer well and you have to water and fertilize more.

“The better-quality medium will save more money,” Bethke says.


Six steps to conducting a valid growing media trial from Chuck Bethke

  • Define the goals for your trial. Are you looking to use less fertilizer, water, use a more sustainable product?
  • Select the product(s) to be trialed.
  • Obtain all of the information available on the product, including spec sheets from manufacturers, recommendations from other growers.
  • Designate an area in the greenhouse, which Bethke says should be the “smallest management unit you can observe.”
  • Assign someone to keep track of the results. During the rush of the season it’s easy to lose track of how the product is performing, how much fertilizer and water you’re using, etc.
  • Replicate results.