This tray of poppies is showing symptoms of iron deficiency, including yellowing of the leaves. Photo: Kaitlyn Sterner, JR Peters
Greenhouse growers know that what the plant doesn’t get from them, it doesn’t get. To achieve optimum growth and plant health, growers and the industry that supports them have developed an entire ecosystem of nutrients, media, testing equipment, and detailed knowledge. But that doesn’t mean problems don’t crop up. We talked to nutrition specialists at Jack’s Fertilizer and Plant Products to find out what nutrient deficiencies they hear about most often, how they present in the growing bay, and what to do about it.
Get it Tested
While yellowing leaves or slow growth can seem to point to a nutrient problem, other issues, like root disease, can masquerade as a nutrient deficiency. Both experts stressed the importance of testing. Visual diagnosis is important, and for a seasoned grower, it can often be sufficient evidence, but media testing, monitoring leachate, and tissue testing can allow growers to make a true assessment. Excess in one nutrient can cause uptake problems with another.
“What we like to see is full picture analysis,” says Kaitlyn Sterner, Director of Technical Support at Jack’s Fertilizers. Start with your water, then look at media samples and tissue testing.
“A media sample is a snapshot of the elements that are available in the root zone the moment that sample is taken,” Sterner says. “Combine that data with tissue analysis, which shows the history of what’s been happening in the plant within the last seven to 10 days.”
But First, Check Your pH
At first, pH seems too simple of a fix, but we all know pH affects the availability of nutrients for plant uptake.
“The importance of pH and managing that in your water is the starting point for a lot of weird things that you might see in the greenhouse. Growers think there’s a nutrient deficiency, but really it’s just pH,” Sterner says.
While a pH adjustment might not completely remedy a problem, it can definitely improve things. “Getting your water tested every year is a great starting point. At the end of the day, managing pH is super important for nutrient availability across the board, both macros and micros,” Sterner says.
Iron
Both experts agree that iron deficiency is one of the more common problems they see day to day. “It could happen in any crop, whether it’s greenhouse vegetables or ornamentals,” says Lorne King, Fertilizer Product Manager at Plant Products. “I’d say it might be more common in ornamentals because (iron) is highly pH dependent. You’re growing different varieties and species that all have varied pH requirements.”
“If pH isn’t within the right parameters, then iron won’t be available for the plant. As pH goes higher, iron availability really goes down,” says Sterner.
Iron is responsible for chlorophyll production and respiration in the plant. When iron is lacking, it’s just less green. Since iron is immobile, the plant can’t pull from older leaves to supply a shortage in the new growth. “Iron deficiency looks like yellowing of the leaves, yellowing of new growth. The older leaves will look fine,” Sterner says.
“With the iron, the way to correct the problem is, number one, check the pH of your media,” says King. Lowering the pH of your feed can help. It’s harder to change the media pH.
When an iron deficiency presents late in the cycle, you may need a fast solution to green up and get the crop out the door. “The quick remedy would be to apply a foliar spray of iron chelate. You could notice a difference within a couple of days. It’s something that you can actually physically see improvement with,” says King.
For a longer-term solution, it’s important to make sure you’re supplying iron in your nutrient program, whether in a blend or adding it as a single element for addition. Sterner explains that any kind of chelated iron is the most available form to the plant.
Calcium
Calcium is a macronutrient that supports cell walls and membranes and serves as an enzyme activator. A lack of calcium may visually manifest as small, stunted new growth, necrosis of the shoot tips, browning at the margins, or leaf curl.
“I see a lot more calcium deficiency issues in vegetable fruits. Calcium is immobile, so the growing conditions have to be optimum for the crop. The plants must be efficiently transpiring. If the plant isn’t transpiring, the calcium is just going to hang out in that older growth. You see it a lot in tomatoes, peppers, cucumbers, and cannabis,” Sterner says.
If your water is hard, your calcium needs may be met with your source water; however, testing is important. Calcium could be present, but an excess of another nutrient can still cause problems. A tissue test will reveal any uptake issues.
Sterner explains that to solve calcium deficiencies in the short term, a one-time corrective drench of calcium nitrate at 200-300 ppm is a great source of calcium. A foliar application also works well. After that, it’s time to figure out the issue to prevent it in the next cycle. “That’s where you have to go back to the drawing board. Work with a fertilizer technical specialist who can help guide your crop steering program from a nutrition standpoint and adjust the fertilizer blends to provide a little more calcium.”
Magnesium
“In greenhouse tomatoes, we almost always see a magnesium deficiency,” King says. “It’s hard to avoid. We see it in tomato crops later in the season.” Magnesium is a somewhat mobile nutrient. The plant can take it from old tissue and move it to the growing point. A magnesium deficiency will be noticed in the older tissue first.
For a magnesium problem, King explains, “The older leaves show interveinal chlorosis. If it was nitrogen, you’ll see a more complete yellowing of the tissue, or maybe even yellowing on other parts of the plant. With potassium, the edges of the older leaves start dying back. You can tell that it’s magnesium – it’s got a very characteristic pattern to it.”
Again, check your pH before jumping to conclusions. “When you’re looking at ornamental crops and see strange discoloration, the first thing to check is your media pH. Send the media for nutrient testing or collect and test leachate from those pots,” says King.
Most growers use magnesium sulfate or magnesium nitrate to provide more magnesium. “If you need more nitrogen anyway, magnesium nitrate is a natural fit,” King says. Ideally, you’re monitoring your feeding and leachate numbers weekly. “The difference between what you’re feeding and what is coming out of your media is a good indication for most elements about what the plant is actually using.”
