Gardeners of any kind need to have the ability to identify plants that are ill. They need to be able to take one look at their plants and determine exactly what is wrong with them. This is even more important for growers of marijuana since they are generally unable to ask others for help and advice.
Not only do you need to be able to diagnose the problem correctly, you also will need to be equipped with the knowledge and tools to fix whatever is ailing your plants. If you can do this pretty well, you will have a much greater chance of succeeding during your first attempt at growing marijuana.
This article about nutrient deficiencies in outdoor marijuana plants will help you improve this skill, therefore increasing your chances of success.
Marijuana nutrient deficiency
Deficiencies are not the only possible problems your plants could have with nutrients. They could also have too much of something, including the three essential nutrients (Nitrogen, Phosphorus, and Potassium). So how can you identify it?
First, reflect on whether what you have been feeding your plant has been completely balanced, specifically with regards to N-P-K. After that, test the pH value of the soil and water that you’ve already been giving them. If the pH levels aren’t perfect, fix them. If they are balanced and your plants are exhibiting symptoms of being unhealthy, then it is possible that the issue is actually connected to the sunlight, as this is not easily controlled by you.
Before you get too confused or overwhelmed by the possibilities, make sure you are identifying it correctly. If your plants are receiving plenty of sunlight and balanced water, the chances are good that the problem lies with the nutrients.
Download my free grow bible to learn more about nutrient deficiencies.
Identify lack of nutrients
The most likely explanation for your plant’s unhealthiness is a lack of nutrients in the soil, or the roots’ inability to absorb the nutrients that actually are there. The challenge with this is not actually providing soil amendments, as they will easily provide your plant with the necessary nutrients. The challenge is actually identifying which nutrients are causing the trouble.
You can look at the different symptoms that your plants are exhibiting, but just looking can be tricky because some nutrient deficiencies will appear the same to the untrained eye. If after reading about what the different deficiencies look like you are still unable to be sure of which nutrient your plant is lacking, you can try flushing the soil with water before you do anything else. This is because a deficiency of one nutrient can be caused by having too much of another nutrient. Too much potassium, for example, could prevent your plant from taking in iron. The process is like this: flush the soil, test the pH level, add whatever you think you need, and then test the pH level one more time.
Testing the pH level is always important, but it is especially so when you need your plants to quickly absorb one or more nutrients. The closer your pH level is to 7, the faster your plant will absorb nutrients of any kind. With any plant, the best way to provide them with a specific nutrient is to through “foliar feeding.” This means to make a tea and spray your plants’ leaves with it. Just be sure to avoid doing this during the middle of the afternoon, when the temperature is at its highest. It is better to do it early in the morning or right when the sun has gone down.
Continue reading for ways to figure out which nutrients your plants are missing out on, along with some information about what exactly each nutrient does, why it is important, and how to fix the deficiency.
Nitrogen is the nutrient that takes care of producing chlorophyll and amino acids. Chlorophyll is essential to the process of photosynthesis while amino acids are what make up proteins, so you can understand why this nutrient is absolutely essential to keeping a healthy plant.
Symptoms of Deficiency
If your plant is experiencing a lack of nitrogen, its symptoms will be mostly seen in older leaves, starting between the base and middle of the plant. Your nitrogen-deficient cannabis plants will look perfectly green at the top, but yellowing more as you look down towards the bottom. Your plant is at the greatest risk for a nitrogen deficiency when it is in its flowering phase. This is because cannabis plants store nutrients in its leaves, and the flowering phase will require this stored cache, thus using up all that it has.
Your concern should grow if the plant is in its vegetation phase. This is simply because the plant needs healthy, green leaves in order to catch as much sun and produce as much energy as possible so that it can continue to grow. If the leaves are yellow, they won’t help in this process.
How to Treat It
You will need to find a way to quickly increase the amount of nitrogen that your plant is absorbing. Blood meal is one easy way of doing this, as are dried blood, cottonseed meal, bat guano (also known as bat manure), fish meal (also known as fish emulsion), or worm castings (worm “manure”). You can pick any of these up at your local gardening store, or at the very least they are readily available on the internet.
Although the yellow leaves won’t ever return to their green state and will instead simply fall off the plant, this doesn’t mean that your plant won’t recover. If treated correctly and promptly, your plant should recover within a week, and new green leaves will replace the lost yellow ones. Before and after you add the soil amendments, be sure you are testing the pH level, as it could increase or decrease when you are treating the nutrient deficiency.
Phosphorus is primarily responsible for helping your plant grow roots, as well as increasing the strength of its leaves and stems. It also aids in seedling germination, making it an especially important nutrient during your plant’s flowering phase. Don’t be dainty when providing your plant with phosphorus; it is usually necessary in hefty quantities.
Symptoms of Deficiency
If your plant is not taking in enough phosphorus, its growth will slow down, and it will generally appear more frail and lacking life. The leaves’ edges on your cannabis plant will lose their vibrant green color – they may even turn brown – and will start to curl in. These symptoms are more likely to appear during the coldest days of the growing season since this is the time when marijuana plants often have the most difficult time absorbing phosphorus from the soil. In addition to the cold, if the soil is too wet or too alkaline, the same problems will occur.
How to treat it
A greater infusion of phosphorus may be necessary during times of the colder temperatures. You can buy fertilizers and plant foods containing phosphorus. As long as the N-P-K ratio exceeds 5, the substance will be helpful for your plant’s phosphorus deficiency. There are also certain all-purpose plant foods (Miracle-gro, for example) that could work just as well. If you use them, you will need to use only half of how much is recommended on the package – an overdose could be lethal for your plants.
Bonemeal, worm castings, and bat guano also provide quite a bit of phosphorus. A harder-to-find solution would be crab shell or crab meal. Many growers use this for any problem that comes up with their plants, but it has a special ability to help with phosphorus deficiencies. Results should be evident within a week.
Just like the other two nutrients of the primary three, potassium is extremely important for your plant to function properly. Potassium is primarily responsible for your plant’s water respiration and resistance of most diseases. Not only that, but it also is helpful in the photosynthesis production and conversion processes. Finally, potassium assists in the water circulation, helping to move water through the entirety of your plant, making it especially important for the flowering and vegetative phases.
Symptoms of Deficiency
Plants that are lacking in potassium will have very slow-growing leaves that might look like they are burnt on their tips and edges. Marijuana plants that are not as rigid, or are easily bent or broken (by you or by the wind) might also be lacking potassium. For existing mature leaves, they might appear mottled and yellow in some specific areas (between the veins at first, then the entire leaf). These leaves may also become completely yellow and die. Because marijuana plants with a potassium deficiency will grow much slower, its most harmful effect is that your flowering phase would be delayed.
How to Treat it
Because marijuana plants easily and quickly absorb potassium, this particular deficiency should be easily fixed. Even if the pH level isn’t perfect, it still should be able to absorb the nutrient quickly and efficiently. One way to combat a lack of potassium is by adding a fertilizer that has potassium to your store-bought fertilizer (if you are already using it). If you would prefer an organic method, you can also use wood ashes, kelp meal, granite dust, or sulfate of potash. You should see results within a week.
These specific deficiencies are not the only problems that your plant might encounter, but it is a good starting point to make sure your plants have the basic level of health that they need. As long as your plants have these three foundational nutrients, they will at least be healthy enough to achieve a decent harvest. As with any problems that might arise when you grow marijuana, early detection is the most important factor in keeping healthy plants and having a successful harvest.
Thanks for reading. Please leave comments or questions below and don’t forget to download my free grow bible.
Greeting Robert! Thank you so much for all that you do! I had health problems for years been a patient in SoCal for nearly 10 years on and off. This year to get started on a hobby I can safely do…I decided to take my hand at decorating pots, planters and start growing on a whim…from 10 clones in mid April and by May I have 8 survivors. It’s a bit late for me to order your products to ward off bugs and promote growth in my final month and hopefully through mid October…I’m using a local nurserys fertilizer that makes most all my regular plants perfect and it’s from a place called moon valley nursery (they sell regular plants). I am starting to worry about some possibily being stunted and I am curious how much to actually water and spray them (water and hydrogen peroxide or water with diluted Epsom salts). Any tips on things I can do on a budget back home is much appreciated. I really enjoy this; I need to start getting over the stigma and go all in with videos of all my awesome plants and favorites…I typically only vape. This however, is my new love, creating and enjoying things I do all on my own then the thrill of the fruits of my labor.. Anyhow, it’s really really hot here in north Hollywood and I grow outside. The soil isn’t always 2 inches dry on top and I don’t want to over water, at times if I feel the pits drain slow I even poke in the terracotta pots from the bottom with bbq skewers to ensure great drainage. If you ever expand in need of a California rep I’d love to say I’ve worked with the man who literally took the time to help everyone on their own personal journey. I am always learning more and now more as I go thanks to your articles most of all!
thanks for the info. I still cant find my problem exactly I’m about 6 weeks in flowering and all my fan leaves are looking burnt and brown spot all over them and they break off very easy.. If you think you could help email me back and i’ll send a pic or tell you more about whats going on.. Once again thanks..
Absolutely not! The fan leaves will help shield the plant. The fan leaves would die before the flower. The flower will need the fan leave to be there in dry conditions. Hope you do not mind the poetic license. 🙂
My plants have been in ground 40 days Toronto can we are in a heat wave for days should I remove the fan leaves I was told to thanks
wo number short,
It means; As long as you n-p-k ratio is 5-5-5. Or; As long a the phosphorous is at 5 (N-5-K) It will be beneficial.
“As long as the N-P-K ratio exceeds 5, the substance will be helpful for your plant’s phosphorus deficiency.”
What is meant by this?? 5 isn’t a ratio.
Hi MD HABIBUR RHAMAN, it’s probably best to upload a picture and describe your situation on our grow support forum. Our experts there are able to help you out with your problem.
I am a first time grower, i have a decent size outdoor grow between my husband and i. I have then in an area with a lot of sun light so i think part of my problem is burnning, howerver i think i am also getting a build up of salt??? my lower leaves are yellowing on edges, and i uppers are curling up, some also have yellowing of veins, all have burt tips… im lost. should i add an N-P-K. see if that helps or is there a way to test for excess sal
Hi sully420, Without knowing your grow methods, in pots or not, what fertilizer used, what is PH of soil, we cannot hazard a guess. Best hop onto the support forum where our experts can help you out
I am a first time grower, i have a decent size outdoor grow between my husband and i. I have then in an area with a lot of sun light so i think part of my problem is burnning, howerver i think i am also getting a build up of salt??? my lower leaves are yellowing on edges, and i uppers are curling up, some also have yellowing of veins, all have burt tips… im lost. should i add an N-P-K. see if that helps or is there a way to test for excess salt??? HELP… lol -sully420
Hi Laura, our support people can help you out 😀 – I❤️GM
I have repeatedly tried to download your free bible but can’t. Any other way of getting it?
It sounds like a bad PH issue leading to a Nitrogen toxicity. I strongly advise you to join our support forum and share a couple pictures after doing some reading from our GrowFAQ section. We have many helpful and friendly members and staff always willing to help out a new grower. 🙂 See you there, lw
Not sure on strain exactly but a lot of the leaves have curled over like a claw and the leaf stems have gone very brittle and flowering has slowed down was just wondering what might be the issue ball park answer is fine is an outdoor grow
Thanks in advance
I stake my seedlings until they are strong enough to stand straight. Bamboo skewers and bread ties work great.
Hi Gary, I think our experts need more information to help you out. They stand ready to look into your problem on our support forum. Be sure to upload some pics and some more information abouth your grow (watering, nutrients, strain, lighting, etc.)
A few of my 3 week old plants are falling over, maybe they are top heavy. Is this from too much water?.
Yes! I advise you to become a member of our support forum. we have many expert growers on site and willing to help you identify your issue. We will need you to fill out a support ticket and add a picture of 2 once you gain posting permissions.
I would ask for a picture but, you cannot post an image. Please join our support forum and our knowledgeable members and expert staff will be glad to help you out. 🙂
Growing first time indoors under 300A LED. Golden Goat clone, growing in organic mulch, fertilizing every 5 days with dyna-gro 1/2 strength. Leaves showing tiny yellow spots, almost like pollen. New growth abundant, but yellowing is increasing. Suggestions?
I have a marijuana plant that has had purple stems and purple stalk its whole cycle…does anyone know what kind of strand it could possibly be??
Are you sure the plant is OK?
I strongly suggest that you join our support forum. Do some reading and fill out a support ticket for us to evaluate, and then we can help you through all the issue you may have. See you there 🙂
Thank you! My plants are showing signs of yellowing, the tips of the leaves are turning brown, like burning. The budds are looking good. I would like to know if their is a way to get the buddy I have to Bush out more?
Nitrogen deficiency does not show up on lower leaves. They are either being used up by the plant and die off naturally, or you are over watering them, most likely. This is common. I can only assume you are outdoors due to your complaint about slugs.
Perhaps joining our support forum will allow you to gain information from our many helpful members.
Happy growing 🙂
MJ plants grow leaves with different amounts of fingers at different times during it’s life cycle. Strains vary.
Happy growing, lw
Thank You FyshhTrap,
Hello, I am a new grower. I ordered three white widow autos. I have been encountering problems with slugs, and also i have noticed that the lower leaves are discoloring, i believe it is a lack of nitrogen. I am only having issues with one as of now, it is also in the flowering stage. I am not sure if its normal in the flowering stage. Any advice would be greatly appreciated.
White flies. Yes they will suck your plants dry. I had same problem, I purchased ladybugs, fixed that problem.
What if my plants is growing leaves with only 3 edges insted of 5 or 7 like a normal plant ?? Should I be worry
another great article, I have seen these deficiencies in the past outdoor grows, and have easily identified two major ones. The fixes seem very simple now as well as preventive care, ie… testing soil before hand etc..
S Central KY here. Stick with indicas or indica crosses. That’s what I do along with autoflowers.
I always strongly advise people to really look through our seed shop. I have always found that you would be the best to decide the characteristics of a plant, the effects, and finishing time.
I also think it would be a good idea for you to join our support forum and meet many growers who may have valued opinions in regards to your query 🙂
I desperately need help choosing my seeds. I live in North/Central Kentucky, U.S.A. Plz someone help me figure this out.
Without knowing what you are feeding this plant, or what medium you are using, etc. It is hard to diagnose what causes your issue. Please consider joining our support forum where we have tons of useful information and qualified experts to help you grow successfully.
Meanwhile; Search Nutrient deficiency’s/mobiles in cannabis.
Finally; Download and read Robert’s Free Grow Bible
It is probably a deficiency problem or burn
Need help with seedling growing in coco seedling stem is turning purple
Having problems with seedling
Red stems are possibly a sign of magnesium deficiencies. However; It is hard to diagnose issues without proper data about your grow methods.
You are right. MG soil is not the best for growing cannabis, but can be used efficiently, if proper grow techniques, and nutrient amendments are employed.
Epsom Salts (MgSo4) Magnesium Sulfate, was the right way to go upon recognizing “red stems”
The real question is: What is the PH of your soil? What is PH of runoff? If PH is off; Soil may be good, nutrients good, but PH being off too far, causes deficiencies.
Perhaps it would be a great idea for you to join our Support Forum. We will be glad to assist you in growing successfully. 🙂
This is my first grow. I have 3 outdoor plants in 5-gal buckets that are moving into the flowering stage. Since mid-summer I’ve had RED STEMS and yellowing and dropping of the older leaves. I used Miracle Gro once a week to treat for several weeks, but I thought I was doing more harm than good. I saw some online articles that said stay away from Miracle Gro! I also read online somewhere that a magnesium deficiency is a cause of red stems so I tried Epsom salts. The yellowing has continued despite all my efforts. The plants seem healthy otherwise, but I want to ensure that they receive optimum nutrition for this crucial flowering phase! Do you have any advice?
My two plants are out side lots of sun. My problem the leaves are turning lime green and black spots on the leaves. A few of the leaver are dead. the phis good water and soil. The plants are in 8 & 10 gal. pots. Please help.
Hi Jason sounds like you might have whiteflies. This article might help you out.You can also join our support forum, if you post pictures our expert growers can help you faster.
I have a bunch of little white flying bugs on my outdoor crop. Do you know what they are and will they hurt my plant? And if so what can I do?
Sounds like a bug pest infestation. Given that you have probably not changed the feeding regimen from moving the plants outside from inside, my guess is you may have an infestation of thrips and/or white fly. If ants are present, that is a sign of possible aphid attack. Also, check how much direct sunlight exposure your plants are getting. Curling and spotting could easily be sunburn as well, so you might move your plants into some shade for awhile and see if they improve. Given that your question was posted on 6/18 and my response is being given on 7/28, either it’s too late or you’ve figured it out and things are improved.
I need help my babies started Inside now are outside and now they spots on the leaves and curling HELP