From a grower’s perspective, a growing media trial is fairly simple: they’re growing the plants they always do in a new growing media.
“The word ‘trial’ makes it sound like a complicated process, but it’s really not,” says Stephanie Cruz, grower specialist for Sun Gro. “It’s as simple as putting a plant in a different growing media and seeing how it performs compared to everything else.”
From there, the grower evaluates how the plant performs. On the ornamental side, that means looking for differences visually. On the food production side, if the grower is selling transplants, that means ensuring the plants grow uniformly across the growing media.
When the results aren’t what the grower anticipated, it’s easy to blame the growing media. “It’s visible,” she explains. “It’s something you can see with your eyes and it’s where the roots grow.”
So, what really goes wrong? Cruz points to three culprits: irrigation practices, water chemistry, and fertilization.
1. Irrigation Practices
Irrigation is one of the main reasons why growing media trials fail. Whether it’s overirrigating or underirrigating, both negatively impact how plants perform in a trial. Luckily, there are clear warning signs growers can watch for each one.
- Overirrigation: A clear sign growers are overirrigating their plants is when algae builds up at the top of the substrate. “If you’re irrigating and also dosing in fertilizer, you will have a lot of algae float to the top of the substrate,” Cruz says. “The plants will also stay pretty small.”
Another common sign of overirrigation is stunted plant growth and roots that aren’t growing as well in the pot.
- Underirrigation: When plants don’t get enough water, that stunts their growth as well. Irrigation is a huge cost for growers, especially where labor is concerned. Some growers will put a sprinkler in the middle of their growing field and hope it irrigates all of their plants.
“If they’re able to have control over how much water goes into each container, that would be really helpful in how we evaluate the substrate,” Cruz adds.
Irrigation is especially tricky for growers that cultivate different plant species at different stages in the growing cycle. This could mean that two-week old plants in one-gallon containers are placed next to large, vigorous plants that are bigger than the pots themselves.
2. Water Chemistry
Water chemistry doesn’t leave the same visible clues, as there’s no algae buildup or stunted root to point to. The water can look, feel, and behave normally while working against the growing media beneath it.
“You want to understand what’s in your water, mainly your alkalinity, because that will affect how you can actually control the pH in your growing media,” Cruz explains.
Alkalinity in water neutralizes acids, which leads to increasing substrate pH if it’s too high, and causes the pH to crash if it’s too low.
- High alkalinity. When water has high alkalinity levels, it raises the pH in the substrate, breaks down pesticides, causes iron deficiency, and keeps the plant from absorbing the nutrients it needs.
- Low alkalinity. When water has low alkalinity levels, it makes the pH in growing media more likely to spike or crash. As a result, toxicities and nutrient deficiencies become much more common.
3. Fertilization Practices
Like water chemistry, fertilization problems can hide in plain sight. A grower might be feeding their plants correctly on paper and still see poor performance because how and when the fertilizer is applied matters just as much as what’s in the mix.
According to Cruz, having a regular fertilizer regime is essential for getting your plants the nutrients they need. This is especially important during growing media trials, as each supplier will have a different amount of starter fertilizer charge.
“You’ll want to keep that in mind when you’re fertilizing,” Cruz says. “Just to make sure you’re continuously monitoring electric conductivity (EC) in the root zone by doing pour-through tests.”
Once a grower performs a pour-through test, they can tell whether their plant has too much fertilizer, too little fertilizer, or the pH is wrong.
Here’s how the test works:
- Water the plant normally. Then wait an hour and pour a small amount of pure water on top.
- Catch the drip water. Hold a plastic cup or saucer under the plant to catch the water that drips from the bottom.
- Test the water. Check the pH and EC in the water sample collected.
If growing media has low EC, it means the plants aren’t getting enough salt from the fertilizer. This can result in stunted plant growth and yellowed plant leaves from not getting enough nutrients.
On the other hand, if growing media has high EC, it means the plants are getting too much fertilizer. This can cause plants to wilt even if the growing media is still moist and their leaves to yellow.
Across all three variables, the pattern is the same: what looks like a media problem is actually a management problem. The growing media trial isn’t a test of the media at all. It’s a test of everything the grower does around it.