Nutrient Toxicity: What Is It And How Does It Affect Cannabis Plants?

A nutrient burn or nutrient toxicity is what happens when your enthusiasm for growing a cannabis plant goes too far, which is why it is often known as the novice’s lament — this is one of the most common mistakes novice growers commit. It’s not surprising; most people believe more is better, so they end up giving more nutrients than needed to their cannabis plants.

In reality, giving your cannabis plant more nutrients than it needs can be a big mistake as you'll find out soon enough. This can cause nutrient toxicity or burning in the plant. And while there are many reasons why this problem may occur, the most common one is human error. 

What is Nutrient Toxicity or Burn?

But what exactly is nutrient toxicity? It’s when your cannabis plant is fed more nutrients than it requires. This can manifest in the plant in many ways, including burnt leaves, stunted growth, low yield, and even death in some severe cases. 

Unfortunately, your cannabis plant isn’t like us. Meaning, it won’t get fat even if it consumes a lot of nutrients, which is what happens if we consume a lot of food. Instead, it thrives with a balanced diet at all times, which is true for us as well. 

Fortunately, a nutrient burn can be treated and even reversed in some cases if you are prompt and smart about it. It may not always be easy, but it is possible. 

What Causes Nutrient Toxicity in Cannabis?

Nutrient toxicity can be caused due to several reasons, but the most common one, as mentioned above, is human error. In many cases, new growers mistake overfeeding for healthy buds, but that’s not the case. 

But keeping human error aside, your cannabis plant may face nutrient toxicity for some other reasons, as well. Here are some of the most common causes of nutrient toxicity in cannabis plants. 

• Wrong Nutrient Ratios 

Your cannabis plant needs three macronutrients (nitrogen, phosphorus, and potassium) and numerous other micronutrients. So, don’t add micronutrients in the same quantity as macronutrients. You also can’t add loads of macronutrients just because the plants need them more in comparison to micronutrients. Remember, it should also be balanced.  

So, if you don’t mix your nutrient solution well or add more nutrients than recommended, expect your cannabis plant to suffer from nutrient toxicity. This can happen during any phase of growth but it is the deadliest for seedlings while vegetative plants can still get by. 

The same applies to bloom boosters or any other kind of nutritional supplements like growth stimulants, especially synthetic or chemical ones, which are more potent and fast-releasing than organic ones. Also, growth stimulants can cause dwarfism in your cannabis plant. 

• Overwatering 

Overwatering can be one of the worst things you can do to your cannabis plant. Not only can it cause nutrient toxicity, but it can also cause various other problems like slimy roots, root rot, drowning, etc. 

Coming to its relation to nutrient toxicity — water from most sources contains minerals and nutrients already, especially tap or well water. This is why many growers simply feed their plants with regular water. 

Here, if you overwater your cannabis plant with tap water or hard water, it can suffer from nutrient toxicity. Another way this can happen is if you are adding nutrients to regular unfiltered water — even if you are adding the recommended amount, the solution will still have more nutrients than necessary. 

• Low Light Conditions 

Lighting is fundamental for your plant’s health, so if you don’t give your cannabis plant enough light, it can suffer from various problems, including nutrient toxicity. How so? 

Your cannabis plant uses light to produce energy, and this is done by converting the nutrients it absorbs from the soil into energy/sugars. When your plant does not get enough light, it won’t be able to turn nutrients into energy efficiently. 

As a result, even if the plant consumes the right amount of nutrients, it can suffer from nutrient toxicity since it will have a lot left in reserve due to a lack of efficient photosynthesis.

• Hot Soil

Rich or living soil is one of the best things you can do if you want to grow cannabis in soil and as organically as possible. But sometimes, this can backfire if the soil is too hot for your cannabis plant to handle. Ask growers that plant their little seedlings in hot super soil! Although the soil is exceptional, you must use regular soil as a buffer so the plants don’t suffer. 

Essentially, hot soil contains nutrients in excess, which causes nutrient toxicity. This usually happens if the soil is enriched with excessive nutrients or fresh manure. 

• Dry Soil 

On the other hand, nutrient toxicity can also be caused by dry soil. Essentially, when your soil dries out too much too often, various nutrient salts can accumulate within the soil instead of washing out. 

When you water your plant the next time, these nutrients can mobilize and get absorbed by your cannabis plant. So, your plant not only gets the nutrients in the water but also the accumulated ones, leading to nutrient toxicity. 

How to Identify Nutrient Toxicity in Cannabis Plants?

Spotting nutrient toxicity can be a bit confusing, but it’s not impossible. If you’ve got a keen eye and some patience, you can spot nutrient toxicity efficiently in your cannabis plant. But what do you need to look out for? Here are some signs and symptoms of nutrient toxicity in cannabis plants. 

One of the first signs that your cannabis plant may be suffering from nutrient toxicity is if it is already suffering from nitrogen toxicity. This is because nitrogen is needed by your cannabis plant in the most quantities, so if it is getting too many nutrients from the solution, nitrogen toxicity will usually be the first thing that shows on the surface. 

This is not to say that nutrient toxicity cannot occur due to other nutrients. Sometimes, you may add a lot of micronutrients, too. We will discuss various other types in the next few sections. 

Apart from that, you will notice the following symptoms on your cannabis plant if it’s suffering from nutrient toxicity:

• The leaf tips may start burning 
• Leaves turning deep green 
• The leaf tips will turn bright, almost fluorescent 
• The tips may also bend at a right angle
• The branches and stems may turn deep red or purple 
• The calyx tips and sugar leaves may start yellowing and withering, and they may also look engorged 
• The leaves may start curling or turning brown

In most cases, nutrient toxicity will begin at the tip of the leaves. This is because the plant wants to distribute extra minerals throughout itself and to do so, it ends up concentrating more nutrients on the tips. It’s like reaching the end of the road.  

Remember, nutrient toxicity is a slow and gradual process at the beginning if you are only giving a little more nutrients than your plant can handle. But if you give a lot of it too quickly, the condition can progress just as rapidly. So, don’t take it for granted. 

If you don’t take the right actions, your cannabis plant may even suffer from a chronic overdose, which can cause your entire plant to turn yellow and wild within a night. After this point, recovery is usually not possible.  

Distinguishing Nutrient Toxicity with Other Conditions 

Here’s the thing — nutrient toxicity in general is an amalgamation of various nutrient toxicities. At the same time, it is easy to confuse these symptoms with some other common cannabis problems. Here are some tips on distinguishing nutrient toxicity from other such conditions. 

Remember the key symptoms of nutrient burn:

• Yellowing or browning leaf tips 
• Crispy or twisted leaf ends 
• Discoloration that spreads over time 
• Curling or clawing leaves with spots 

Nutrient Deficiency

Ironically, nutrient deficiency is easy to confuse with nutrient toxicity. So, look for symptoms like completely yellow leaves or wilting leaves. These two signs are enough to distinguish the two conditions. 

Watering Problems 

When you overwater or underwater your cannabis plant, it will show some serious symptoms, but this problem shares various symptoms with nutrient toxicity, including curling leaves, rust spots on the leaves, and clawing of the leaves. 

So, look out for exclusive watering problems symptoms like completely yellow leaves, bronze patches on the leaves, drooping plants, and wilting. Additionally, overwatered cannabis may also show symptoms like saturated soil, and shiny and thick leaves. 

Excess Heat or Light 

Lastly, your plant may suffer from heat stress if the canopy is placed too close to the grow lights or the HVAC temperature is not dialed in for your cannabis plant. This problem will also show symptoms like curling leaves. 

Fortunately, distinguishing heat/light stress is very easy. If this is the case, all the symptoms will appear close to the light or the source of heat. For example, if your plant is too close to the light, the symptoms will develop on the top of the canopy first. 

Types of Nutrient Toxicity

It’s pretty difficult to identify other types of nutrient toxicity, unlike nitrogen. This is because the symptoms of nitrogen toxicity are much too obvious while the symptoms of other types coincide with other issues. Typically, an imbalance or excess of one nutrient manifests as a deficiency of another nutrient, so you can’t say for certain if it’s a toxicity of one nutrient or a deficiency of another. Nevertheless, understanding a bit more about them may help you fix problems if you know what you’re looking for. 

• Nitrogen Toxicity

As mentioned earlier, your cannabis plant will likely show signs of nitrogen toxicity during the onset of nutrient toxicity. So, you must learn how to distinguish the two; if not, you might end up starving your plant or giving it too much nutrients. 

Nitrogen is one of the three macronutrients required by your cannabis plant, and it plays a massive role in enzymes and amino acids. But too much nitrogen is never a good thing for cannabis. 

One major symptom of nitrogen toxicity is browning or yellowing leaf tips, but that’s the same as nutrient toxicity. Instead, look for other symptoms like dark leaves, completely yellow leaves, or leaves turning smooth and shiny. 

Prevention and Treatment

Adjust the nitrogen levels in fertilizers based on the stages of plant growth. In addition, use well-balanced formulations. Purchase fertilizers from branded companies so you know exactly what you’re feeding. Finally, flush the plants with water to remove any nitrogen.

• Phosphorus Toxicity

Phosphorus is crucial for the development of flowers and roots, but excessive levels can lead to toxicity. Since phosphorus helps the plants form huge buds, many growers use large amounts in the hope that they will get big yields of high-quality buds. This is why bloom boosters are so much in demand. However, using them excessively can be harmful to plants. 

Symptoms

Phosphorus toxicity can cause deficiencies in other nutrients like zinc and iron as it’s all about maintaining the right balance. In other words, you will see a major nutrient lockout where the plant is unable to absorb other nutrients. 

For this reason, you will see symptoms of other nutrient deficiencies with the leaves showing various discolorations at times, depending on the nutrient that’s locked out. The plant will also display stunted growth with reduced flowering capabilities. 

Prevention and Treatment

Use fertilizers with proper ratios that contain appropriate amounts of all macro and micronutrients. Flush the plant quite a few times with plain pH-adjusted water to remove any toxicity. 

• Potassium Toxicity

Potassium is essential for plant health. It serves as a regulator and maintains various processes including activating enzymes, water uptake, and a lot more. Suffice it to say that the plant simply can't survive without it. However, as always, excessive levels can lead to toxicity. Using potassium-based fertilizers excessively to improve the size of the buds can cause this problem. 

Symptoms

Excess amounts of potassium can prevent the plant from absorbing other nutrients like calcium and magnesium. Thus, you will see symptoms that are similar to these nutrients in the plant. Typically, the plants will display stunted growth. It will also experience salt stress and the leaves may start wilting and even look crispy and burned. Needless to say, the plant will find it hard to grow properly, so you’ll also see stunted growth. 

Prevention and Treatment

Maintain a balanced nutrient profile and adjust the levels of potassium based on the growth stages of the plants. To get rid of excess potassium, flush the plants. Then, use a balanced fertilizer after the plants recoup. 

• Calcium Toxicity

Calcium helps to develop and strengthen cell walls to maintain the plant’s structural integrity. It also helps to activate enzymes, and signal processes while helping with nutrient transportation. 

Symptoms

Calcium toxicity can result in leaf tip burns and necrosis as distorted or stunted growth. To prevent and treat calcium toxicity, it's important to monitor the levels of calcium in the soil or growing medium and adjust supplementation accordingly. Additionally, maintaining pH levels is crucial for nutrient absorption. Calcium toxicity will also interfere with the plant’s ability to take in potassium and magnesium. So, you will see symptoms that match those deficiencies. 

Prevention and Treatment

As always, use fertilizers that contain proper ratios of nutrients. Calcium toxicity can also increase the plant’s vulnerability to heat stress. In hydroponic systems, just change the entire solution and start from scratch. For soil, flush the plants until the runoff is clear. Use pH-balanced water or you’ll have problems again. 

• Magnesium Toxicity

Magnesium is an important element that aids in many processes. Not only does it help with chlorophyll production but it also aids in photosynthesis, making it a valuable nutrient for cannabis. Most importantly, it helps in the transportation of phosphorus in the plant which ultimately helps it develop big buds — the only thing you need. However, large amounts can create more problems. 

Symptoms

Magnesium toxicity can prevent the plant from taking up potassium and calcium, so you must take care of the problem immediately. You may see purple discolorations on the stems as well. Other symptoms include chlorosis (yellowing between leaf veins) leaf curling or twisting well and reduced growth and flowering.

Prevention and Treatment

To prevent and treat magnesium toxicity, you should first flush the plants until the run-off water is clear and shows the correct pH. You can next add Epsom salts in recommended quantities; however, it’s best to go with a proper fertilizer that contains balanced nutrients and add Epsom salts only if it’s required. 

Cannabis plants can also suffer from other toxicities like sulfur which occurs if you’re using soil that already contains excessive amounts. Symptoms are similar to nitrogen deficiency, but leaves may also turn brittle.  

Finally, cannabis plants may also experience toxicities of micronutrients like iron and zinc although it’s rare. Typically, this occurs if you add extra amounts of micronutrients without calculating the right amounts. Although you can make your own nutrients from scratch as it could get expensive over time, it’s best to stick to commercial formulations if you don’t have the experience. 

Coming to iron toxicity, the plants will show symptoms such as scorched leaf tips, and leaf discoloration with yellowing between veins along with reduced growth and flowering. Zinc toxicity will show up as leaf chlorosis (yellowing), stunted growth, and curling or distortion of leaves. 

Cannabis plants can also experience boron, manganese, and copper toxicity but it’s very rare. To address any toxicity, it’s important to flush the plants. However, always make use of pH-balanced water and take care not to overwater the plants. If the leaves droop too much, place the containers near fans so the soil dries up quickly. 

Can You Save Your Plant from Nutrient Toxicity? 

Nutrient toxicity sounds like a serious issue, and it is, but fortunately, it can be reversed or the plant can be saved in most cases. Of course, this depends entirely on the health and condition of your plant and how serious the problem was to begin with. If your plant suffers from nutrient toxicity for a short while, it won’t even affect the yield at all. 

But if the condition is too serious, your response is too lax, or your plant wasn’t healthy, to begin with, your plant may not be able to recover from nutrient toxicity. In such cases, there’s always a risk of losing your plant entirely. 

How your plant is protected from nutrient toxicity also depends on which growth stage it is going through. 

If your cannabis plant is merely a seedling, you might want to say your final goodbye to it. Seedlings don’t need a lot of nutrients, so if you end up overfeeding it, it may not bounce back at all. Even if you can save your seedlings, it will still be a long, arduous process, and in most cases, autoflowering seedlings won’t be salvageable. 

On the other hand, if your cannabis plant is suffering while it’s in the vegetative stage, you’re in luck. Take prompt action here and protect your plant. Just note that your plant may need some time to recover and it may lose some of its vigor along the way, so it might not grow as tall as you’d expect it to. 

Things are not the same during the flowering stage. Generally, nutrient toxicity isn’t forgiving if your cannabis plant is in the flowering stage because this is where nutrients matter a lot for the eventual yield and your buds don’t give your plant the luxury of recovery time. 

If you end up feeding your cannabis plant too much during the late flowering stage, your plant is in trouble. It may even die. So, if your plant is close to harvest, don’t try to fix the problem. Minimize the symptoms and harvest your buds as soon as possible to cut your losses. 

Remember, nutrient toxicity can affect the quality of your cannabis buds, too, especially if the problem occurs during the bloom stage. In the flowering stage, your plant’s nutritional requirements change and it no longer needs nitrogen but needs calcium and magnesium. 

If your plant suffers from nutrient toxicity during this stage, the buds may seem a bit burnt and may taste a bit different. 

How to Fix Nutrient Toxicity in Cannabis Plants?

As serious as nutrient toxicity is in cannabis plants and as tricky it is to identify, it is rather easy to fix for most growers. Once you have identified this problem properly, you need to be prompt and start taking some steps. 

The first thing you should do is carefully and gently prune all the plant materials that appear damaged. So, if some leaves are damaged, cut them off. You can also remove calyx clusters — do so by removing the entire florette. 

Unfortunately, the problem can’t be reversed, so if you leave the damaged parts as is, they may start rotting, which is an entirely different, rather deadly problem for your cannabis plant. So, swallow the hard pill and cut them off. 

Next, you need to flush your cannabis plant’s growing medium with RO water a couple of times. Make sure the water is pH balanced just to add another layer of redundancy to the process. If you are using a reservoir to store the nutrient solution, you should also measure the EC of the solution. 

Don’t go through so much hassle if you are growing cannabis in a hydroponic setup. Simply give your hydroponic plumbing a good flush and swap out the nutrient solution for a recalibrated, pH-balanced, and milder solution. 

After this, you need to start feeding your cannabis plant again, but you need to keep a few things in mind here. First, measure the EC and pH of the nutrient solution using an EC pen and pH pen. Ideally, the pH of a cannabis plant should be between 5.5 to 6.5 in hydroponic systems, and the EC/PPM should be as follows: 

• 500 to 600 PPM for seedlings
• 800 to 900 PPM for the vegetative stage 
• 1000 to 1100 PPM for the flowering stage 
• 400 to 500 during the pre-harvest or late-flowering stage 

Before you start feeding your cannabis plant once again, you should use plant tonic to give your plant a boost in recovery. During nutrient toxicity, the soil also gets damaged a bit, so this tonic will not only restore the plant’s health but also the soil’s. This is because it is rich in humic and fulvic acids, minerals, silver nitrate, and vitamins. 

After that, you can start regular feeding but don’t use the same nutrient ratios as before. Be more conservative and only use ¾ of what you used to use to prepare your nutrient solution. 

Soon enough, your plant will recover and gain its vigor. Still, allow it a couple of weeks to recover fully and ensure it does not experience any more stress during this time. 

How to Prevent Nutrient Toxicity in Cannabis Plants?

As with any other problem that plagues cannabis plants, prevention is always better than cure. So, you must do everything you can to prevent nutrient toxicity in your cannabis plants. And here are some steps to do that. 

• Keep Your Plant’s Growth Stage in Mind 

Cannabis plants need different ratios of nutrients during each growth stage. For example, during the vegetative stage, it requires more nitrogen to grow a dense canopy and put on bulk. Come flowering and your plant will switch to using more phosphorus and potassium. 

So, study your strain and give it the nutrients it needs during its growth stage. One shoe does not fit all — treat your plant like Cinderella. 

• Keep an Eye on the PPM 

As mentioned earlier, you need to keep an eye on the PPM levels of your nutrient solution. So, use the readings recommended earlier even when your plant is not suffering from nutrient toxicity to prevent this problem from occuring. 

• Be Conservative When Using Feeding Charts 

Remember how we keep recommending that you start with a small dose any time you are trying a new cannabis product? Use the same principle on your cannabis plant. When feeding it, be conservative with the nutrients since it’s always easier to give your plant a nutrient boost (with a foliar spray) than cutting it back. 

If you are using feeding charts or recommended concentrations, you should always take the recommended numbers as being maximum. So, use 50% to 70% during the start to be on the safer side of things. 

• Use Products Made for Cannabis 

If you are purchasing your nutrients or supplements from your local store, only use cannabis-specific products, no matter what the salesperson may try to push. Cannabis-specific products are designed with this plant in mind, so you won’t have to worry about giving your plant the wrong nutrients. 

• Feed Your Cannabis Plant Properly 

All the things listed above cumulate to this point — feeding your cannabis plant properly. Follow the listed steps and you’re almost there. To finish it off, here are some points to keep in mind that will help you feed your cannabis plant better:

• Do not feed your plant any nutrients for the first two weeks of the seedling stage 
• Only use quarter-strength nutrients during the rest of the seedling stage 
• Give your plant more nitrogen during the vegetative stage 
• Give your plant more phosphorus and potassium during the flowering stage
• Only water your plant when the top inch of the soil is dry and water it until 25% of the water runs out of the bottom 

Summary: Nutrient Toxicity: What Is It And How Does It Affect Cannabis Plants?

Nutrient toxicity is a toxic condition, pun intended, for your cannabis plant. Unfortunately, the most common red flag in this “toxicity” is grower error. So, understand the risks and the causes of nutrient toxicity and learn to be the best grower version of yourself. 

Next, keep other common causes in mind and ensure you prevent them by being mindful about how you feed your cannabis plant, especially the nutrient ratios, PPM levels, water quality, and pH levels. 

If your plant does experience nutrient toxicity, don’t sweat it. Be prompt, flush the plant, give it some tonic, and let it recover. Don’t forget to dilute your nutrient solution for the future.