Before you try to treat cannabis plant deficiencies, you need to know for sure, what the problem is. Just because your plants may look like they are deficient in a particular nutrient, it doesn't mean that they are!
In this guide we will go through the most common cause of cannabis plant deficiencies, how to fix them, and how to prevent them arising in the future.
By the end of this guide, you will have all the resources you need to diagnose and treat most deficiencies quickly.
If you need urgent help with a cannabis plant deficiency, feel free to ask for help in our cannabis growers forum
There are three things that are the cause of the vast majority of cannabis plant deficiencies. As you become more experienced with growing cannabis, you will be able to predict when deficiencies may arise, and treat them before they cause a problem.
It takes time and practise, but even the most experienced growers will suffer deficiencies now and again.
Cannabis Plant Diet
As the plant progresses through its life cycle, its needs for nutrients will change.
Vegging plant will prefer a high dose of Nitrogen in their feed
Flowering plants prefer higher Potassium and Phosphorus, with a lower nitrogen dosage
The first main cause of cannabis plant deficiencies is an imbalance in PH
Ph of your grow medium is an important factor in your plants diet. If the Ph of the medium is off balance, the plant will not be able to use up the available nutrients.
The first thing you need to check when your cannabis plants display symptoms of a deficiency is the ph of the medium.
In soil, the PH of the medium is easier to control, and has a wider "buffer". Most soils will be fine with pH between 6.5 and 7.5. You can check this by measure the pH of the run off, after watering your plants.
For hydroponic systems, including coco, the pH of the medium needs to be between 5.8, and 6.2. There is no pH buffer in coco or hydro, so you need to make sure that the level are within this range.
Check the pH of your reservoir in hydro setups, or measure the run off after feeding your plants in coco. If the pH isn't in the correct range, this could be the cause of your problem. Correct that, before increasing the feed.
If the Ph is within the correct range, then the next likely cause is a lack of sufficient nutrients in the medium. You maybe need to increase the dosage in your next feed to supplement the deficiency.
In soil grows, it can be harder to diagnose what the problem is, as soil will contain nutrients in the medium, before you add any.
It can be difficult to know what your plants has in the medium, and what it needs.
When you are growing cannabis in hydroponics, it is easier to tell if you plant is going to suffer from a deficiency by monitoring the run off, or EC of the reservoir.
If the Ec of the run of is lower, than the EC of the nutrient solution, you need to increase the EC in the next feed.
If you are growing in full hydro system, montor the reservoir levels to know exactly what your plant needs, by following these charts:
Sometimes, your plants will display signs of deficiency, even though they have plenty of nutrients available to them. This may be caused by a salt build up. If this is the case, you should flush the medium straight away.
Salt build up is when synthetic nutrients have built up in the medium.This can block the roots of your plants, and stop them from eating and drinking.
If you over feed your plants, the roots will essentially get clogged by excess salts.
The plants won't be able to eat or drink, and they will show signs of deficiency very quickly.
The problem here, is some growers will instantly assume, the plant need more food, when the case is, it needs less, much less.
Make sure you monitor the EC of your reservoir and run off, any steep rises in EC can be a sign of a salt build up, flush the medium straight away, or change the res.
Using the correct kind of nutrients for the right stage of growth will help keep your plants healthy and deficiency free. But at the same time, you need to use the right amount.
A flowering plant doesn't need a higher EC than vegging plants, it needs different nutrients.
In the early stage of growth, you plants will need very little food. Don't over do it. If you over feed your plants at this stage, you could kill them. It's always better to underfeed than over feed.
If you're growing in soil, use a potting mix for seedlings and small plants. Or, mix the soil you intend to use with 50% coco, 50% soil. This will reduce the EC of the soil, and will not shock the young plants and seedlings too much.
For hydro growers, feed your plants a small dose of "grow " nutrient from your chosen brand. The EC should be just 0.2 points over your BG EC. That will be plenty for the first week of growth.
Through the Vegetative stage of the cannabis plants life cycle, it will grow stems, leaves and branches. To do this, it needs a lot of Nitrogen.
Grow foods are higher in Nitrogen than other minerals, you will see this by the NPK ratio. Use grow nuits, and slowly increase the dosage as the plants grow bigger.
Monitor the Ec of the run off, or reservoir to make sure it isn't rising. Feed light, and feed often, rather than feed heavy, less often.
During the flowering stage, the cannabis plant will need less nitrogen. It will stop growing leaves stems and branches, and work on growing buds.
The plant will still need nitrogen, but less of it, the main demand will be for P and K, Phosphorus and Potassium.
Bloom nutrients will accommodate for this, by reduce the concentration of nitrogen, and increase the concentration of potassium and phosphorus.
It is important to use the correct nutrients, for the correct stage of growth. When your cannabis plants begin to flower, use bloom nutrients.
The Calcium Magnesium deficiency is commonly diagnosed, but not accurately. Most salt based nutrients that come in an A & B two part bottle set, have a good amount of calcium in them.
Also, if you're using tap water, there is a good chance there is calcium carbonate in the water, which can be used by the plant for calcium.
Calcium deficiency comes when there is a lack of magnesium. Magnesium is used in conjunction with calcium, with out Mag, the Cal cannot be processed properly.
Be careful with treating a cal mag problem, feed calcium lightly to the plant as there is probably plenty waiting to be used. You just need a bump in magnesium. Which can be done with a foliar feed of epsom salts.
During flower the demand for potassium and phosphorus becomes much higher. Using Bloom food will help with this high demand, and adding a PK booster to your feed will benefit the grow.
Using a PK booster during the stages of flower will keep deficiencies away, during the most important time of growth. If you're not using a PK booster during flower, it is likely you will see signs of P and K deficiency.
The four most common cannabis plant deficiencies are, Nitrogen, Potassium, Phosphorus, and Calcium.
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Nitrogen deficiency will most likely be seen during the middle stages of veg, and during the stretch. This is when cannabis plants will use the most nitrogen.
The plant will begin to look pale, and lose it shade of green. The plant will not have what it needs to build stems and branches, so it will slow down growth, and could end up being a small, stumpy plant.
If leaves at the bottom of the plant are turning yellow, and falling off, it is down to nitrogen deficiency, or lack of light to the lower leaves.
Due to the feeding schedule needed when growing soil, you will come across a Nitrogen deficiency before any other.
When a cannabis plant is in veg, it will use up a lot of nitrogen. The plant will use up all of the nitrogen in the soil, faster than other nutrients, so you will see nitrogen deficiency first.
You should introduce "grow" nutrients at this point, or transplant your plant into some new soil, in a bigger pot. Increasing the nitrogen content of the medium will fix the problem.
Be light with the dose, you do not want to over feed your plants. Adding 0.5ml per Litre to your next feed should see the problem solved in a few days.
When treating any one of the cannabis plant deficiencies, make sure the pH of the medium is in the correct range, for soils, that tends to be between 6.5 and 7.5
If you are suffering from a nitrogen deficiency in a cannabis plant when growing in hydro or coco, it can be fixed quickly. If your plant starts to look pale, and the leaves at the bottom start to fall off, you could be seeing a nitrogen deficiency.
Check the EC of the feed, and of the run off. If the EC of the runoff is lower than the EC of the feed, or the EC of the reservoir is falling, you need to raise the EC a little. This will bring more nutrients to the plants.
Use "grow" foods, as they are high in nitrogen, and raise the EC of your feed by 0.2 points. This will fix the problem within 24 hours.
Make sure the pH of the feed, and/ or medium, is set to the correct levels. For hydro growing, that is between 5.8, and 6.2.
Potassium is used for many things in a cannabis plant. It helps the plant breathe, moves nutrients around to where they need to be, and gives the plants energy.
A potassium deficiency in a cannabis plant will affect the plant in many ways, as it will slow down the transportation of nutrients. Without potassium, you plant doesn't have the strength it needs to grow to its full potential.
During the flowering period, a cannabis plant will need a lot more energy to grow the buds. So a boost in potassium will be needed. If you have not added a PK booster to your feed during the flowering stage, you may be seeing a potassium deficiency.
Before you add more food to the medium, you should check on your watering schedule. If you're overwatering your plants, they will display sign of potassium deficiency too.
Your soil needs to dry out a little between water, and your plants should never sit in run off. If you suspect that you may have been over watering, hold off the feed and let the medium dry out a little. See if it fixes the problem.
If you have been watering your plants correctly, then you may be lacking phosphorus in the medium. You should use a " bloom" feed to fix this, as it will be high in potassium. Be light with the feed, and only add 0.5ml per litre to the next feed, and see how the plants respond.
Check the pH of the soil, and adjust if necessary, it should be between 6.5 and 7.5.
A potassium deficiency in hydro, will most likely show up during the late flowering period.
It takes a lot of energy to build those buds, and your plant needs potassium to get that energy. There is also more plant to feed, and as phosphorus transports water and nutrients around a plant, you need more of it.
Check the EC of your run off, if it is lower than the EC of your feed, you need to increase the EC of your next feed by 0.2 points. If the EC of your reservoir is falling, you should also raise the Ec in the res by 0.2 points.
The Ph of your medium is vital to optimal nutrient uptake. Make sure it is balanced between 5.8 and 6.2. If it isn't, you will have nutrient lock out, and you plant will not be able to eat properly, regardless of what you feed it. Flush the medium to rest the PH to the correct range.
Phosphorus is a very important element to plant growth. It is responsible for nutrient uptake, formation of roots, and overall health of your cannabis plants.
It responsible for many biochemical reactions, and with out it, your plants essentially, cannot digest their food properly.
Without a decent level of phosphorus, your plant will be stunted, and weak. It will also be more susceptible to pest and disease as its immune system will also be weakened.
Increase the amount of phosphorus in the medium by adding some bloom food, or a PK booster to your next feed. Like any nutrient deficiency, treatment should be taken lightly, don't over do it with the dosage.
Gradual increase in the amount of nutrient you provide to your plant will make sure you do not overfeed and cause toxicity or excess.
Add 0.5ml per litre of a Bloom feed to your next feed, and see how the plant reacts.
Also check the ph of the medium by reading the runoff. It should be between the levels of 6.5 and 7.5
Phosphorus deficiency in cannabis plant will usually arise during the flowering stage of growth. This is when the demand to phosphorus is at its highest.
Most growers will supplement the need for phosphorus with a PK booster during flower to prevent a deficiency from arising.
Use a good bloom feed, and monitor the EC of the feed and runoff, to determine if your plants are eating enough.
If the ec of the run off, or res, is lower than the feed going in, then you should raise the EC of the next feed by 0.2 points. This will provide a little more food to your plants, and the deficiency should fade within a few days.
Always make sure the pH of the medium, and of the feed, is within the ideal range, of between 58, and 6.2.
Calcium deficiency is one of the most diagnosed cannabis plant deficiency. Growers see problems and instantly assume its a cal/mag issue, and pour calcium and magnesium nutrients through the medium.
This can make things worse. Calcium and magnesium work in conjunction with each other. There is usually plenty of calcium available to your plants in the A & B nutrients you're using, and your tap water.
What usually causes a calcium problem, is a lack of magnesium. Without magnesium, calcium can not be broken down properly by the plant, so though there might be plenty of calcium in the medium, it is not available to the plant.
During veg, your plant should have plenty of cal mag in the medium. As the flowering stage approaches the need for calcium will be higher.
To combat this, you should folia feed your plants with epsom salts. Dissolve 1 tablespoon into five litres, ( 1/4 tbs for 1 l is fine) and mist your plants with a fine spray, a few days before you "flip" them to flower, and again, just as flowers begin to form.
This should combat a calcium and magnesium deficiency.
If your BG EC is low, you're using RO water or Distilled water, you may need to supplement ment with a cal mag nutrient, as there isn't any trace calcium in your water. But be very light on the dosage, and watch your plants for changes.
Instead of adding extra salts to your medium, and increasing the EC, you should folia feed your plants with epsom salts to treat a calcium deficiency.
Calcium and magnesium work together, magnesium with break down the calcium making it available to the plant. It doesn't matter how much calcium you feed your plants, if there isn't enough magnesium, the calcium can not be used.
By spraying your plants with a fine mist of 1/4 tbs per litre of epsom salts, you will give the plant the magnesium it needs, to break down the calcium in the medium, and in the water.
Supplement calcium if you're using water with a very low BG EC, such as distilled, Reverse osmosis, or spring water. Tap water usually has a good amount of background salts in it, and some of these are calcium. So be careful when adding cal/mag to your feed.
Make sure your ph is on point! 5.8-6.2, adjust it if it is out of balance.
This is just scratching the surface, there are a lot of cannabis plant deficiencies that may arise during your grow. Some of them may be out of your control. Even the very best growers have plant problems, its how they react and fix them that make them good growers.
Make sure the roots zone, and feed, is always around 18c. If it's too cold, you can shock your plants, and they will shut down and stop drinking. If it is too warm, you encourage bad bacteria to start growing, and your plants will suffer with root rot.
If you leaves are damaged by nuit burn, or patches, it is not likely they will return back to full health. The damage is done. You need to watch new grow, or unaffected growth, for any changes.
Leave the damaged leaves where they are, they might no look nice, but the plant still uses them, only remove them when you're defoliating your plants at set times in the life cycle.
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