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Psuedo-Nutrient Deficiencies in Cannabis

Troubleshooting the most common and elusive nutrient deficiency

One of the biggest time-wasters I’ve seen among cannabis cultivators, regardless of cultivation style, is to obsess over nutrient deficiencies. It makes sense, to a point: cannabis is a fast-growing, heavy-feeding plant. And there are a staggering number of strains and phenotypes, each with its own quirks. It’s essential to understand basic plant nutrition, and to respond to nutrient deficiencies in a timely fashion. But what if that plant that appears to have a nutrient deficiency is actually suffering from root damage, or reduced capacity for healthy transpiration because the air conditioner broke? In that instance, does it help to douse plants with more CalMag? Actually, it might make things worse.

Cannabis-specific nutrient companies have formulated a dazzling array of products to feed our plants, each promising to deliver the best cannabis recipe the world has ever seen. Many successful nutrient companies have cult followings who swear with zealous fervor that ”Brand X“ is the only worthwhile nutrient line. Only idiots use ”Brand Z“, they say. Maybe Brand X really is the best, but there’s a lot of hype inflating the value of that industry.

Likewise, there’s no bottled substitute for hard work, organizational skill, attention to detail, and experience. Any grower who has been hired to operate a cannabis garden should know how to provide a standard, balanced feeding regimen for all phases of growth in their gardens. It’s really not so complicated a task. Whether the master grower designs her own feeding regimen by mixing a blend of raw materials and bottled products from various suppliers, or she downloads a feeding schedule from a reputable nutrient company and goes with that, she can easily ensure that her plants have the nutrition they need to thrive.

If it’s so easy to feed plants correctly, why do nutrient deficiencies appear so often? What’s with all the growers hounding social media forums with pictures of leaves that appear to be manifesting complex multi-nutrient deficiencies? And why do fellow cultivators respond with fifty different opinions on what nutrient deficiency it could be, providing fifty different methods to correct it? Shouldn’t there be a more definite diagnosis and treatment protocol, as one would find for any other agricultural crop? Where does this confusion stem from?

It’s a simple misunderstanding: That thing that looks like a nutrient deficiency isn’t caused by a lack of available nutrients. Throwing in more iron, calcium, or magnesium won’t fix the problem. It could even make it worse, because you’re likely dealing with a pseudo deficiency.

Here’s a definition, courtesy of the Montana State University Extension Office:

Pseudo (false) deficiency symptoms symptoms (visual symptoms appearing similar to nutrient deficiency symptoms).
Potential factors causing pseudo deficiency include, but are not limited to, disease, drought, excess water, genetic abnormalities, herbicide and pesticide residues, insects, and soil compaction.

I remember an apprentice of mine, five or six years ago. She showed delightful promise as a cultivator and was both smart and hardworking. She allocated much of her free time to cultivation research, in hopes that she could run her own commercial cannabis garden one day. One summer, she showed me some troubling pictures of her small home garden and asked what I thought. Leaves were yellowing, twisted, and splotchy. New growth was sparse and lime-green. These plants appeared to be suffering from a cluster of nutrient deficiencies—too numerous and severe to alleviate. I was stumped. After carefully reviewing her feeding history and her notes, I asked a ”dumb“ question. It was a hot, August summer in Denver. Had her plants become too dry in these hot temperatures (to the point of withering) during the last month or so? Yes, she admitted. Several times.

Those drought events had triggered a powerful pseudo deficiency cascade in her garden, and now it was too late to correct. Her plants, which had been babied with expensive nutrients and amendments, had become dehydrated almost to the point of death, just three weeks before. Although the plants appeared to have recovered above ground, their roots had essentially cooked and dried, dying back to the point they ceased to be able to absorb and assimilate nutrients. Since the plants no longer had a vital root system to absorb food, they were starving. Ironically, it would have done no good to throw more food at these plants that had no capacity to eat that food. Most likely, that would have just made the situation worse.

It’s easy to laugh at my apprentice’s misfortune, but I’ve witnessed several acclaimed growers make similar mistakes. It’s sometimes easier (and sexier) for the grower to present an overly-complicated theory on nutrient lock-out (to stoke the fires of self-importance) and then request $30K to purchase the latest snake oil from their favorite nutrient company. And though the grower may actually believe that the snake oil alleviated their problem, it’s just as likely that the season changed and the HVAC started working better in the fall. In hobby gardens, this miscalculation makes little difference. On a commercial scale the costs are staggering.

Pseudo deficiencies are most often the result of imbalanced environmental conditions. And while some products, like aloe, can alleviate some of the stress related to environmental imbalances, there is no product I’m aware of that will correct the underlying deficiency. The most effective way to treat pseudo deficiencies is to bring the environment into balance. And that’s why commercial cultivators need to invest in the best environmental infrastructure. If you’re going to shell out big money, start with HVAC.

It makes sense that cannabis would present pseudo deficiencies more often than most agricultural crops, because with cannabis we artificially create our environmental conditions. We used artificial lighting, artificial heating and cooling, artificial day/night parameters, and often artificial fertilizer to create the most productive gardens possible. Plant nutrition isn’t that difficult to decipher, but creating perfectly balanced environmental conditions is both difficult and expensive. If environmental parameters aren’t conducive to the essential metabolic functions of your plants (photosynthesis, respiration, and transpiration), pseudo deficiencies will inevitably arise. I’ve been in hundreds of private and commercial cannabis gardens, and I’ve yet to encounter a single one that didn’t struggle to balance heating, cooling, and dehumidification.

In the coming weeks, I’ll follow up with a slightly more technical post dedicated to fixing pseudo deficiencies, but I’ll leave you with these basics: The next time you see plant health taking a turn for the worse, before you pull out your nutrient deficiency chart, evaluate whether you are experiencing (or have recently experienced) any of the following potential causes for a pseudo deficiency instead:

  • 1.Lack of water: If grow media gets too dry, roots will die. Check irrigation lines and irrigation timers to make sure water is flowing evenly and frequently enough. Additionally, check to see if soil is compacted or hydrophobic. Sometimes very dry soil will repel water.
  • 2.Too much water: Plants can drown. Overly saturated soil can kill roots and invite disease. If you see algae on the surface of your soil, it generally means it’s too wet.
  • 3.High humidity (above 55%RH), Stagnant air: Plants won’t take in as much water (or the nutrients within the water/soil media), and pathogens will thrive.
  • 4.Low humidity (below 40%RH): Transpiration happens too rapidly, sucking up massive quantities of water. If grow media or nutrient solution is too concentrated for long periods of time, this can result in toxic shock.
  • 5.Fluctuating humidity: Plants respond metabolically to humidity, and are easily stressed by continuous, rapid humidity fluctuations, as is common when using dehumidifiers on an ON/OFF humidistat.
  • 6.Too much light: Can burn plants.
  • 7.Too little light: Causes etoliation, reduces yield and quality.
  • 8.Pests: Can damage plant tissue, interfering with the transport of sugar and nutrients within the plant. Some pests spread viruses.
  • 9.Pathogens: Most common pathogens are easily identified powdery mildew and botrytis, but other viruses, rusts, etc. can result from contact with infected plants, infected tools, airborne spores, etc. Pathogens can easily create pseudo deficiencies in plants, but be careful to evaluate any underlying causes for the presence of pathogens in your garden and attempt to alleviate the root cause, in addition to treating outbreaks.
Cassandra Maffey
Cofounder and CEO of Fire Tower. Cassandra is the creator of Scalable Living Soil, an organic, high-volume cultivation system powering large-scale producers around the country. Recently named one of High Times' Top 50 Women in Cannabis.