In the world of cannabis cultivation, there’s a term that has long been used among growers that we think is time to package and be done with:
This catch-all phrase incorporates a very complicated series of physiological processes happening in cannabis plants that had been fed too much or too little of one or more nutrients. It incorporates so many–yet not all–of them that it’s essentially meaningless. It leaves out other factors that may be to blame for physical abnormalities that you may observe on growing cannabis.
So, we’re putting $1 in the swear jar every time we hear it moving forward. To properly diagnose nutrient-related issues, it’s time we developed a more comprehensive understanding of what’s going on in the grow room … and call them by their names.
Any abnormality that develops on growing cannabis plants is an indicator that something is out of balance, and can essentially be traced to three issues:
This is why it’s crucial to go into diagnosing issues with a full understanding of all the possible variables. Is it really nutrient imbalance that’s causing your plant leaves to change colors, curl up, and possibly even cause damage to your plants? Let’s dig into each in more detail.
When nutrients aren’t properly monitored, you might notice imperfections on your plants’ foliage. These blemishes are tell-tale signs that there’s too much or too little something.
Great news: Now you just have to figure out what.
This could be as simple as not feeding plants the right nutrients at the right time. Or it could be a symptom of something more serious.
When you notice a physical abnormality, it’s crucial to diagnose the problem quickly. You can do this by isolating nutrients, and testing variable levels of them on a few different plants one at a time until you find it.
During these tests, it’s important to keep notes and document your observations so you and your team can learn from this experience and fine-tune going forward.
Knowledge is power; the more metrics you can collect and log about the issues you’re having with your plants, the easier it will be to know for next time.
Nutrient imbalance can also be caused by over- or underfeeding your plants. Both are very easy to do, as nutrients affect each other differently in a growing cannabis plant, and can even change depending on what stage of growth your cannabis plant is in at the moment.
Some of the most common nutrient deficiencies during the vegetative stage are nitrogen, magnesium, and sulfur. During the flowering stage, the most common nutrient deficiencies are iron, potassium, and phosphorus.
Here’s a very basic breakdown of the visual appearance of these deficiencies on cannabis plants:
Iron - This deficiency can be very hard to distinguish from a magnesium deficiency. The best tactic to take is to boost the use of fertilizers that have both nutrients, because if one type of deficiency is occurring, it’s likely the other is soon to follow.
Potassium - Flowering cannabis plants use a lot of potassium since it’s the nutrient that helps buds swell in size. This deficiency shows up via a yellowing and almost burned appearance on the edges of the blades of leaves.
Phosphorus - Although deficiencies are rare with cannabis plants, they can still happen. When older leaves start to show brown spotting (or another dark color), growth has slowed, and new leaves are smaller than usual, it might be due to a phosphorus deficiency.
Nitrogen - Cannabis needs more nitrogen during the flowering phase compared to the vegetative phase, which can sometimes lead growers to not feed plants enough during veg. A nitrogen deficiency becomes apparent when leaves progressively turn yellow, beginning at the bottom and traveling upward to the top of the plant.
If you’ve experimented with these nutrients and you still haven’t isolated the cause of the imbalance, there are a few other nutrients that can lead to deficiencies that cultivators should be aware of. These are the signs:
Zinc - Younger leaves start yellowing in between veins give this one away.
Manganese - Yellowing leaves and brown spots (which are sometimes confused with phosphorus deficiencies) make this apparent.
Calcium - Younger leaves that curl could be a sign of a lack of calcium.
Copper - Plant leaves that get dark and shiny could be a sign that copper is needed.
It’s important to always go by the manufacturer’s instructions for feeding your own combinations of nutes. Combining certain nutrients together and applying them at the same time to feed your plants can lead to nutrient uptake deficiencies, too. We recommend taking an in-depth educational course to learn how cannabis interacts with nutrients to get a more complete understanding of this physical phenomenon and how it affects the health of your plants.
Water can contribute to weird things happening on the leaves of your plants, too. Improper watering will affect nutrient intake, so it’s important to have a good gauge of what’s going on in your substrate before damage starts to happen to your plants.
Alternatively, your plant’s pH might be out of range. Cannabis plants love water that’s close to a 7 pH (neutral), and even the smallest deviations from that can have drastic effects on their health and growth.
We recommend investing in the technology and tools, such as EC sensors like the TEROS 12, to give you an accurate understanding of the contents of your water in your substrate.
Overwatering and underwatering can both shock your plants, which will affect its nutrient uptake, as well. For example, if a cannabis plant is not being fed enough water, it won’t be able to absorb enough nutrients. On the other hand, if a cannabis plant is being watered too often, it won’t be able to absorb enough nutrients.
We advise maintaining and logging a consistent feeding and watering schedule–one that’s appropriate for each phase of growth–which can help you keep track and learn what your plants need.
Finally, your environment could be a factor causing your cannabis plants to change shapes and colors.
Relative humidity (RH) is one variable in the greenhouse or grow room that has huge effects at the cellular level on your growing plants. From the clone room to the veg room to the flowering room, all the way to the final stages of flowering, all require specific ranges of RH to catalyze the processes in the plant to grow to its full potential.
If your cannabis plants are not growing under optimal lighting conditions, that could also play a part in the physical symptoms you’re seeing developing on your cannabis plants. Light shock and stress harm your plants in ways that mimic the look of many nutrient deficiencies, so don’t forget to consider this elemental factor when diagnosing your problem.
Get a sense of what’s going on in your substrate. It’s important to solve nutrient imbalances in cannabis cultivation quickly, as problems can affect your plants and ultimately your yields. We advise relying on substrate sensors for more accurate monitoring and measuring of EC, which will allow you to keep tabs on your substrate’s conditions and nutrient levels.
If you can, bring a sample in for a leaf tissue analysis, which is the quickest way to get an answer to nutrient imbalance issues. That way you can dial in on the problem before you lose productivity and the problem damages your plants.
And make sure you maintain a log of your feeding schedule. Consistently keeping track of your feeding regimen will allow you to look back at what worked well for your plants, and learn for the next run. It’s easy to do with the right software, like the AROYA Kiosk, which gives you and your team the tools to communicate quickly across facilities if schedules are changed or an issue is identified on cannabis.
It can't be restated enough: when crop steering cannabis, any kind of deficiency is loss of efficiency. That means at the end of the day, whether it’s a nutrient imbalance, environmental imbalance, or something to do with your watering schedule, the longer it takes to diagnose and solve the problem, the more resources it will drain from you. Your time, money, and plants are too valuable for that.
Adopt the right tools to help you accurately measure and monitor what’s going on in your plant's substrate and environment.
(PDF) Characterization of Nutrient Disorders of Cannabis sativa
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pH is a measure of how acidic or alkaline something is. The pH scale ranges from 1–14, with a pH of 7 being neutral (the pH of pure water). If pH is lower than 7, a substance is considered acidic (think vinegar or lemon juice). If the pH is higher than 7, the substance is alkaline, as is the case with soaps, bleach, and ammonia.
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