DocofRock
Well-Known Member
Good afternoon, RIU! I wanted to talk about the process of differential diagnosis for growing cannabis.
Differential diagnosis is a concept borrowed from the field of medicine that means “distinguishing a disease or condition from others that present with similar clinical features”. Let me give you an example.
A patient comes to the clinic with cardiac arrhythmias (irregular heart rhythm), a critically high potassium level, and rapid/labored breathing. This is the presentation of the patient and the symptoms they are expressing. What I just described, however, was NOT a diagnosis, and here is why...
A diagnosis is constructed based on examining the available information, seeking additional information if necessary, and ruling out potential diseases or conditions that present similarly but are due to completely different pathologies.
In the example above, this patient could be in kidney failure - causing a build up of fluid in the lungs (causing the rapid and labored breathing), an elevated serum potassium (glomerular filtration too low to remove electrolytes/fluid from the patient), and arrhythmia because of the electrolyte imbalances and hyperkalemia (potassium level too high). This patient could also be in diabetic ketoacidosis, causing the same symptoms, but for entirely different reasons.
Can we treat the high potassium? Sure. Will it do anything (let’s say in the example of the patient in diabetic ketoacidosis) other than mask the symptoms of the underlying issue? Absolutely not.
So wtf does this have to do with cannabis cultivation?
I’m glad you asked. As it turns out, cannabis plants, much like humans, animals, and other eukaryotic forms of life, are capable of immensely complex biological and cellular processes. Also similar to humans, cannabis wants to and will fight to live in the conditions it is given. Unfortunately, it is only possible for cannabis to be subjected to immense stress and inhospitable conditions for so long. And, as in humans, sometimes you don’t find out what really happened until the autopsy. Maybe if the doctor had really found the underlying disease causing all the symptoms of the patient’s illness, they could have intervened.
A simple, yet incredibly important thing to remember when it comes to growing: your plants’ reaction to and expression of problems are how the plant communicates a problem. As an example, wilting, dry leaves accompanied by nutrient toxicity are the symptoms displayed, but alone, these symptoms don’t tell you the problem. This is where differential diagnosis/critical thinking comes into play. The difference between a novice grower (or novice clinician) and an expert? The novice treats the symptoms, the expert treats the cause.
An example from my latest grow:
Everything seemed to be going fine in the grow tent. My plants were exploding and producing fantastic growth. My environment was within range (at least it appeared), nutrient ratios, pH, and concentrations were correct, and plants were not being overwatered or overwatered. One morning, upon waking, I noticed my plants had wilted, looking almost unrecognizable from the healthy plants I had seen when I went to bed. I knew it wasn’t overwatering or overfeeding. I religiously watch the parameters of my grow, pH everything that even gets brought into the grow room. I’ve been feeding only 650-750 ppm Max to 4 week old plants in coco, and nothing but water to my soil plants of the same age. I just couldn’t figure it out.... at first.
It turns out, in my inexperience with LED lights and my newness to growing indoors, I underestimated the strength of my lights. Worse, I didn’t understand the principles behind voltage, amperage, watts. I thought I knew my lights and, to the best of my ability, estimated the par/PPFD of my lights. What I didn’t understand was the principles of electricity or constant voltage drivers. It turns out, there was no physical way I could have reduced the par intensity using the two fixtures I have in the tent, because turning down the potentiometer and wattage of the lamps to the minimum allowable was STILL too much par energy. Way too much. And no matter how much I turned down the potentiometer, I was still not changing the PPF output much, just wasting electricity, creating heat, and stressing my plants. To figure out what I had ultimately done, I tapped the bank of knowledge I’ve acquired as well as researched. I know my stuff, but sometimes it’s easy to overlook critical factors in your grow, especially while you’re learning. By performing a comprehensive assessment of my plants, environment, and nutrient/water intake, I was able to make a deduction of the likely culprits contributing to my issues.
I could have just stopped feeding my plants, as they were displaying Nitrogen toxicity. As a result, they would have gotten worse, being underfed AND light/heat burned with a high VPD and underwatered conditions. However, it’s almost never as simple (and is usually counter-productive) to adjust a nutrient regimen you KNOW to be within an acceptable ppm/EC range. So WHY did I get the wilting, nitrogen toxic leaves? Well, a combination of things which on their own would not have caused an issue, but all together set off a terrible chain reaction.
My lights were a bit too intense, and a bit to close (even though the PPFD was within acceptable range, at least I thought). This caused a concentrated area of heat and light over abundance (even though the temp was perfectly normal if evaluated by itself - 77F). Coupled with my tendency toward underwatering (in my soil plants - scared of mold). Due to the high temp and light intensity, the vapor pressure deficit climbed to an unacceptable range, causing the plants to increase transpiration, creating dehydration in the leaves, and increased evaporation from the soil. Coupled with a soil with very high organic matter content (rich in N), a decreased ability to perform effective photosynthesis, and an increased need for water (which caused nutes to be taken up too quickly as well), the end result would have been disastrous if I was unable to accurately and quickly determine the issue.
If I can impress one thing upon you, it is simply to think through the situation to the best of your ability. Your plants almost always need a lot less of something you’re providing, and in my case, it was all from too much light. It’s the extremes (in environment/nutes/watering/air circulation or lack there of) that usually set of the chain reactions of negative events. Could the plant have dealt with any one of these issues in isolation? Sure, but there’s hardly anything that occurs in horticulture, medicine, or hell... life itself, that exists in a vacuum. So, if you want to grow good cannabis, back off of the excess and really learn the fundamentals.
As we continue to push the limits of cannabis horticulture, we fly closer to the edge. Lights are more powerful, information is more plentiful, and nutrient lines are more confusing than ever before. Have a problem with your plants? Figure out where you’re just doing too much using some good old fashioned critical thinking, and work on your differential diagnoses. On our perpetual quest towards “more” and “better”, often the answers lie in just getting back to the basics. We all likely smoked weed long before the time when there were 15,000 nutrient lines, 500 online forums, and 3.0 umol/J lighting fixtures. As it turns out, more is not always better.
As we continue to push the limits in cultivation, I foresee problems becoming a lot more frequent and much more confusing. It’s easier to fix a nutrient issue when your regimen consists of a few ingredients than a basket full. A simple feed schedule with adequate light, good air flow, and a well controlled environment will always do you better than adding additional and extraneous variables.
Differential diagnosis is a concept borrowed from the field of medicine that means “distinguishing a disease or condition from others that present with similar clinical features”. Let me give you an example.
A patient comes to the clinic with cardiac arrhythmias (irregular heart rhythm), a critically high potassium level, and rapid/labored breathing. This is the presentation of the patient and the symptoms they are expressing. What I just described, however, was NOT a diagnosis, and here is why...
A diagnosis is constructed based on examining the available information, seeking additional information if necessary, and ruling out potential diseases or conditions that present similarly but are due to completely different pathologies.
In the example above, this patient could be in kidney failure - causing a build up of fluid in the lungs (causing the rapid and labored breathing), an elevated serum potassium (glomerular filtration too low to remove electrolytes/fluid from the patient), and arrhythmia because of the electrolyte imbalances and hyperkalemia (potassium level too high). This patient could also be in diabetic ketoacidosis, causing the same symptoms, but for entirely different reasons.
Can we treat the high potassium? Sure. Will it do anything (let’s say in the example of the patient in diabetic ketoacidosis) other than mask the symptoms of the underlying issue? Absolutely not.
So wtf does this have to do with cannabis cultivation?
I’m glad you asked. As it turns out, cannabis plants, much like humans, animals, and other eukaryotic forms of life, are capable of immensely complex biological and cellular processes. Also similar to humans, cannabis wants to and will fight to live in the conditions it is given. Unfortunately, it is only possible for cannabis to be subjected to immense stress and inhospitable conditions for so long. And, as in humans, sometimes you don’t find out what really happened until the autopsy. Maybe if the doctor had really found the underlying disease causing all the symptoms of the patient’s illness, they could have intervened.
A simple, yet incredibly important thing to remember when it comes to growing: your plants’ reaction to and expression of problems are how the plant communicates a problem. As an example, wilting, dry leaves accompanied by nutrient toxicity are the symptoms displayed, but alone, these symptoms don’t tell you the problem. This is where differential diagnosis/critical thinking comes into play. The difference between a novice grower (or novice clinician) and an expert? The novice treats the symptoms, the expert treats the cause.
An example from my latest grow:
Everything seemed to be going fine in the grow tent. My plants were exploding and producing fantastic growth. My environment was within range (at least it appeared), nutrient ratios, pH, and concentrations were correct, and plants were not being overwatered or overwatered. One morning, upon waking, I noticed my plants had wilted, looking almost unrecognizable from the healthy plants I had seen when I went to bed. I knew it wasn’t overwatering or overfeeding. I religiously watch the parameters of my grow, pH everything that even gets brought into the grow room. I’ve been feeding only 650-750 ppm Max to 4 week old plants in coco, and nothing but water to my soil plants of the same age. I just couldn’t figure it out.... at first.
It turns out, in my inexperience with LED lights and my newness to growing indoors, I underestimated the strength of my lights. Worse, I didn’t understand the principles behind voltage, amperage, watts. I thought I knew my lights and, to the best of my ability, estimated the par/PPFD of my lights. What I didn’t understand was the principles of electricity or constant voltage drivers. It turns out, there was no physical way I could have reduced the par intensity using the two fixtures I have in the tent, because turning down the potentiometer and wattage of the lamps to the minimum allowable was STILL too much par energy. Way too much. And no matter how much I turned down the potentiometer, I was still not changing the PPF output much, just wasting electricity, creating heat, and stressing my plants. To figure out what I had ultimately done, I tapped the bank of knowledge I’ve acquired as well as researched. I know my stuff, but sometimes it’s easy to overlook critical factors in your grow, especially while you’re learning. By performing a comprehensive assessment of my plants, environment, and nutrient/water intake, I was able to make a deduction of the likely culprits contributing to my issues.
I could have just stopped feeding my plants, as they were displaying Nitrogen toxicity. As a result, they would have gotten worse, being underfed AND light/heat burned with a high VPD and underwatered conditions. However, it’s almost never as simple (and is usually counter-productive) to adjust a nutrient regimen you KNOW to be within an acceptable ppm/EC range. So WHY did I get the wilting, nitrogen toxic leaves? Well, a combination of things which on their own would not have caused an issue, but all together set off a terrible chain reaction.
My lights were a bit too intense, and a bit to close (even though the PPFD was within acceptable range, at least I thought). This caused a concentrated area of heat and light over abundance (even though the temp was perfectly normal if evaluated by itself - 77F). Coupled with my tendency toward underwatering (in my soil plants - scared of mold). Due to the high temp and light intensity, the vapor pressure deficit climbed to an unacceptable range, causing the plants to increase transpiration, creating dehydration in the leaves, and increased evaporation from the soil. Coupled with a soil with very high organic matter content (rich in N), a decreased ability to perform effective photosynthesis, and an increased need for water (which caused nutes to be taken up too quickly as well), the end result would have been disastrous if I was unable to accurately and quickly determine the issue.
If I can impress one thing upon you, it is simply to think through the situation to the best of your ability. Your plants almost always need a lot less of something you’re providing, and in my case, it was all from too much light. It’s the extremes (in environment/nutes/watering/air circulation or lack there of) that usually set of the chain reactions of negative events. Could the plant have dealt with any one of these issues in isolation? Sure, but there’s hardly anything that occurs in horticulture, medicine, or hell... life itself, that exists in a vacuum. So, if you want to grow good cannabis, back off of the excess and really learn the fundamentals.
As we continue to push the limits of cannabis horticulture, we fly closer to the edge. Lights are more powerful, information is more plentiful, and nutrient lines are more confusing than ever before. Have a problem with your plants? Figure out where you’re just doing too much using some good old fashioned critical thinking, and work on your differential diagnoses. On our perpetual quest towards “more” and “better”, often the answers lie in just getting back to the basics. We all likely smoked weed long before the time when there were 15,000 nutrient lines, 500 online forums, and 3.0 umol/J lighting fixtures. As it turns out, more is not always better.
As we continue to push the limits in cultivation, I foresee problems becoming a lot more frequent and much more confusing. It’s easier to fix a nutrient issue when your regimen consists of a few ingredients than a basket full. A simple feed schedule with adequate light, good air flow, and a well controlled environment will always do you better than adding additional and extraneous variables.