Something wrong? Sample your growing media

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Researchers from Oklahoma State University Extension give their recommendations on how to prepare samples for accurate readings.

Photo: ©bnenin | Adobestock

Greenhouse growth media, also called soilless growth media, is commonly used in greenhouse, raised bed and container crop production. Media is primarily made up of peat moss, perlite, vermiculite, bark, sand and possibly other ingredients, with properties distinctly different from regular field soil.

Therefore, testing soilless growth media requires sampling procedures, test methods and interpretations different from those used for routine field soil testing. A routine soilless growth media test is indispensable to nutrient management for optimal plant performance, problem prevention or diagnosis.

The Oklahoma State University Soil, Water and Forage Analytical Laboratory (SWFAL) offers a greenhouse growth media test using the Saturated Media Extract (SME) method. The same method is used by most university and commercial labs to test soilless growth media or growth media with very little soil in it. In this method, the samples submitted by growers are saturated with a solution containing a small amount of chemical, allowed to equilibrate for a few hours, then the extracts are drained for analyses.

Typically, pH, soluble salts and major macro- and micro-nutrients are analyzed. Following the sampling procedures and interpretation guidelines listed below is essential to make the test useful and reliable for you to make decisions about proper nutrient management.

Sampling methods best practices

The procedures to take samples for soilless growth media tests affect the accuracy and representativeness of the results. Incorrect sampling can lead to misleading results, interpretations and recommendations. The goal is to collect samples representative of the overall chemical properties of the growth media for the group of plants of interest.

Following the steps below can help achieve this goal:

  1. Determine the right time for sampling and keep it consistent. Avoid taking samples immediately after irrigation, heavy rainfall or fertilizer application. Instead, wait for a few hours after irrigation or heavy rainfall, and wait for at least a week after fertilizer application before sampling, if possible.
  2. Sample separately for each different crop. If a problem is to be diagnosed, sample separately from containers with normal and abnormal plants for comparison.
  3. Select the right tool for sample collection, such as a clean trowel for containers and a clean soil sampling probe.
  4. Collect at least 10 cores of media from spots equally distributed across the growing bed, the bulk of media or from 10 containers. The cores can be taken from the top to the bottom of the media or from the root zone. Avoid sampling only from the upper layer, where the level of nutrients and soluble salts is higher than that in the root zone.
  5. Combine the 10 cores in a clean container and mix them well into one sample. Place 3 cups to 1 quart of the combined media into a sample bag and drop it at your local county OSU Extension office to be sent to SWFAL.
  6. If slow-release fertilizers are present, remove them from the sample, if possible, to avoid overestimation of fertility.
  7. Check the root condition and record it when sampling, since such information is useful for interpreting the results.
  8. Record sample information, including the type of growth media (soilless or not, commercial brand), crop, stage of crop development, fertilizer program (specific fertilizer, application rate and frequency), sampling time (relative to irrigation, rainfall if outdoor systems and fertilizer application), root conditions when sampling and symptoms of any problems observed such as stunted growth, yellowing or discoloration of leaves, burning of leaves, etc.
  9. Keep sampling procedures consistent and have samples tested by the same lab so growing conditions can be tracked through time.
  10. Sampling should be done at least once halfway through production or as soon as symptoms such as yellowing, stunting, or leaf abnormalities occur. Realize that correcting a deficiency or toxicity can take two to four weeks, so for short term crops media should be sampled sooner. For longer term crops, soil samples should be taken multiple times throughout production to account for nutrient availability during that crop stage.

Result interpretations and recommendations

Soilless growth media test results include values of pH, electrical conductivity (EC) and individual nutrient levels. The ideal ranges for these values vary depending on the crop, developmental stage or age of the crop, production system and management practices. For result interpretation tables, head to

Photoo: ©Budimir Jevtic | adobe stock

Growing gains > Growing Pains

How the industry is acquring growing media while facing price hikes, supply shortages and more.

By Chris Markham
Market-ready patio pots at Matt's Greenhouse.
Photos courtesy of Matt's greenhouse

As if growers haven’t faced enough challenges the past couple of years, some problems continue to linger. One such problem is acquiring growing media. From shortages to rising costs, many growers have paid extra high prices for the growing media they want, if they could even get the type they want at all, in which case they’ve had to switch to another media to use.

When you’re growing plants, growing media is one of the last things you want to have problems with. Not only is your growing media the foundation of healthy, quality plant growth, but choosing which growing media to use requires considering many different factors, including what plants you’re growing, where you’re growing them and how you’re growing them.

We reached out to growers to see how they’re handling some of these growing media problems.

At Matt’s Greenhouse in Fort Madison, Iowa, Matt Mohrfeld, owner, grows bedding plants, vegetables, herbs, hanging baskets and patio pots. After running the business for more than 40 years, Mohrfeld has been through more than his fair share of media.

Additionally, in Oberlin, Ohio, resides Green Circle Growers, one of the largest greenhouse operations in North America. Sitting on over 120 acres, Marcel Boonekamp, director of growing, and Corwin Graves, vice president of growing, have a lot of growing media to oversee.

The early bird gets the substrates

Through either a stroke of genius or a lucky break — Mohrfeld can’t quite decide — Matt’s Greenhouse has avoided some of the pitfalls surrounding the current state of growing media in the industry. “Do you ever get lucky in life and then you look back and you can say, ‘I’m a genius?’” Mohrfeld says before recalling how his decision to over-order a new growing media made all the difference this year.

Previously, Matt’s Greenhouse used an incorporated control slow-release growing media. However, when Mohrfeld placed the orders last summer, he decided to switch to a stock blend. “We went to a stock blend and added handling equipment to incorporate both slow release and lime, because we’re going to modify the media,” Mohrfeld explains. “Last summer, when we sat down and negotiated and looked at things, I said, ‘You know, I’ll take 15 loads of dirt — 15 loads of soil. I’ll take them right now and I’ll pay you for them as they come.’ And we had our soil in place.” What was really crucial, he adds, was that “because we didn’t have slow release, we overbought by one load.” While so many growers were caught navigating shortages of material, Matt’s Greenhouse was able to acquire a surplus by being the early bird to the dirt.

“And like I said, looking back, I just may well be a genius,” Mohrfeld jokes. “But more pragmatically, we took the opportunity to not get caught up in supply chain interruptions.” Things can always go wrong when running a growing operation. “The stars align badly, driver shortages, truck shortages, input shortages and labor shortage,” Mohrfeld says. “And so, we took advantage of it and said, ‘Hey, ship us everything we ordered,’ but we couldn’t have done that if we would have stayed with the controlled release substrate.”

In a normal year, Mohrfeld says he would’ve done the opposite and under-ordered, instead of over-ordered. “Typically, when things were easy, we would under-commit and then add in that extra load,”when they needed it, likely by the time they got to poinsettia season, he explains. However, since he ordered extra this past summer, Mohrfeld expects their supply to carry them through poinsettia season.

But what happens after poinsettia season? Mohrfeld is optimistic regarding prices and availability when that time comes. “I’m 65 years old,” he says. “I’ve seen a lot, right? I’ve seen that we have a recession every 10 years and I’ve seen a lot of them. I’ve seen the early ‘80s … I’ve seen Y2K … things will level off. They always do.” And there’s truth to that statement. Things can’t stay bad forever, right?

Matt's Greenhouse grows racks of herbs at their Fort Madison, Iowa operation.

More money, more problems

Meanwhile, the folks at Green Circle Growers have seen drastic price increases. “The one trend we’ve seen is that prices are up,” says Graves. “Sometimes 30-40% and other times higher depending on where and who we’re sourcing from.”

What’s driving these price hikes? “Price increases were primarily caused by increase in freight cost,” says Boonekamp. If a grower wasn’t lucky enough to get their fill of growing media before the price hikes, are there ways they can save money? Graves says that Green Circle Growers have “been investigating lower profile grow pots and other strategies that will allow us to fit more within the same cart or trailer.” Unfortunately, saving money on freight transportation remains a difficult task, according to Boonekamp. “It is hard to find big savings, as most of the processes are efficient already,” he says. Instead, Boonekamp recommends that growers ensure they don’t lose money. “Focus is on reducing losses throughout the growing process, whether it is from disease or any other reason we can lose plants.”

Unfortunately, soaring prices aren’t the only problems. While Green Circle Growers hasn’t had any issues with availability of the European pine bark they use for their signature orchids, the same cannot be said for other crops. For the peat moss/wood fiber blend they use in their non-orchid crops, Green Circle Growers has run into some availability issues. “Due to the current challenges around price and availability of peat, we’ve recently increased the inclusion of wood fiber to help offset these challenges,” says Graves. “We’re also looking at so-called ‘peat replacement’ options to further reduce our reliance on peat moss. We are testing a product called EZ Blend from Profile Products, the makers of Hydrafiber.”

At least there’s a lesson to be learned, according to Graves. “We learned that it’s often unwise to place all of one’s eggs within a single basket,” he adds, “as there is a significant risk that a single issue can spiral out of control, leading to massive shortages and interruptions to the production process.

Matt Mohrfeld's growing portfolio also includes hanging baskets.
The folks at Green Circle Growers are fortunate that they haven't run into trouble. sourcing the European pine bark they use for their signature orchids.
Photo courtesy of Matt's greenhouse; Photo by allison krieg

Getting your info

When it comes to getting the most up-to-date, accurate information on growing media mixes and new substrate options, Mohrfeld says he turns to sources like grower seminars from his alma mater, Iowa State University, national publications and e-GRO.

Graves says they work closely with industry consultants, academia and other growers to keep a pulse on what’s happening. Green Circle Growers’ collaboration with other growers for information is a nice reminder that our industry isn’t a zero-sum game. We aren’t in a field where we have to remain closed off from each other. It’s important for growers to work together, talk with each other and learn from each other.

Look ahead, prepare and adapt

Mohrfeld shares one last bit of wisdom: “There’s one thing that we absolutely know for sure, and that is things will change. That’s the truism in life.” Every grower needs to adapt to the shifting demands and challenges of our industry. Today, those challenges take the form of the coronavirus pandemic, substrate shortages and rising prices, among other things. Next year, we might still be seeing some of those same challenges. Or perhaps we’ll see brand new challenges affecting growing media supplies and acquisitions. Whatever happens, growers need to be ready to adapt and face what comes their way.