Every gardener needs to know how to identify plants when they are ill. They should be able to take one look at their plants and determine precisely 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.
Nutrient Deficiencies In Marijuana Plants:
- Do your plants have a nutrient deficiency?
- Nutrients and pH
- Identifying the lack of nutrients
- The big three: macronutrients
- Other potential nutrient deficiencies
- Getting your plants back to health
Not only do you need to be able to diagnose the problem correctly, but 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.
Tip: make sure to download my free Grow Bible for more information
Do your plants have a 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, or N-P-K). So how can you identify it?
First, reflect on whether what you have been feeding your plant has been entirely 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. The nutrients deficiencies can be caused by many things, but the most significant factor is pH value. 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 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.
Nonetheless, it’s important to remember that nutrient deficiencies or disorders in your marijuana plants can occur with every growing technique and in every growing medium; rock wool, soilless, aeroponic and hydroponic or soil. In fact, within the world of cannabis cultivation, nutrients issues are a constant concern. Although the macronutrients (potassium (K), phosphorus (P), and nitrogen (N)) are the usual offenders, you can also end up with calcium, zinc, magnesium, or other imbalances, although these are usually slightly less common.
Indoor marijuana growers usually have more problems with nutrient disorders than outdoor marijuana growers. This is problematic because a nutrient deficiency always slows the growth of the cannabis plants down.
Nutrient disorders sicken the marijuana plant, and a disproportionate amount of nutrients can cause toxicity or nutrient burn. It can also cause the lock-out of other vital minerals. You’ll want to learn how to prevent nutrient deficiencies so that you can increase your chances of success.
Nutrients and pH
How do you know if your plants are deficient? Well, if your plants seem unhealthy, there is a good chance they could have a nutrient deficiency. Usually, you can notice a nutrient deficiency by symptoms in the pH of the water and soil around the plant. A balanced pH is one of the ways you can ensure that your plants absorb all of the nutrients they need.
The pH scale is how growers measure the acidity or alkalinity of the soil and water around their plant. The scale ranges from 1 to 14, with 7 being neutral pH. 1 is the most acidic while 14 is the most basic (alkaline). When you are watering your plants, you want to be entirely sure that the pH levels are appropriate; otherwise, the plants can be damaged, and their health can deteriorate.
Adjusting the pH is simple: all you must do is make the environment (whether soil or water) more alkaline or acidic, depending on its current level. The pH for cannabis should be somewhere near the neutral middle of the pH scale, somewhere around 6 or 7. Although hydroponics systems can sometimes support a cannabis plant with a pH of as low as 5.5, the ideal range is somewhere around 6. Each of the different nutrients that you add or take away from the environment will affect the pH and the general absorption of nutrients by your plant. Understanding this relationship will help you grow the healthiest plants.
Testing the pH level is always important, but it is especially so when you need your plants to quickly absorb one or more nutrients. Testing pH levels is also extremely easy. You only need testing strips or a ph meter from a local gardening supply shop. This will help you avoid over or underfeeding your plants. You should also be able to purchase commercial mixes of soil that easily let you modify and stabilize the pH of your own soil. PH strips and meters are also online available at this link.
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 feed your plants specific nutrients is through “foliar feeding.” This means making a tea and spraying 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.
Identifying the lack of nutrients
Because 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, it’s important to know how to identify which nutrients are posing the issue. In fact, most experienced growers will tell you that the challenge with nutrient deficiencies is not actually providing soil amendments, as they will easily ensure your plant has 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 check the pH level one more time.
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 a deficiency.
The big three: macronutrients
The three deficiencies outlined below 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 (nitrogen, phosphorus, and potassium), 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 essential factor in keeping healthy plants and having a successful harvest. Take a look at what each nutrient is responsible for and how to identify and solve a nutrient deficiency.
Nitrogen is one of the most essential nutrients for healthy plant growth, and because it’s so heavily used by cannabis, it’s not uncommon for plants to develop nitrogen deficiencies. Nitrogen is used for a wide variety of plant processes, from photosynthesis to the production of vital amino acids and chlorophyll. Chlorophyll is essential to the process of photosynthesis while amino acids are what make up proteins so you can understand why this nutrient is vital for 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. In general, the signs of a nitrogen deficiency are yellowing leaves. If the lack is left unchecked, the yellowing leaves can wither and die.
Your nitrogen-deficient cannabis plants will look perfectly green at the top but yellowing more as you look down towards the bottom. Although nitrogen deficiencies will usually begin in the bottom leaves of the plant, they will eventually spread up to the top. 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.
One thing people always ask me is when they should harvest their plants. This free PDF doc gives a perfect idea of when to cut your plants.
Your concern should grow if the plant is in its vegetation phase. This is simply because the plant needs healthy, green leaves 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.
Some growers describe seeing symptoms such as the leaves curling over like a claw, with the leaf stems going very brittle. The leaves may also turn a very dark shade of green. If it’s during the flowering phase, the flowering will likely have slowed down as well. In this case, it is probably a pH issue that is leading to nitrogen toxicity. That means that your plant actually has too much nitrogen, but not because you are feeding it too much; instead, it is due to a pH imbalance.
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.
You should also make sure that you’re using a fertilizer which contains the right ratio of macronutrients: nitrogen, phosphorus, and potassium. Plants require extra nitrogen during the vegetative stage of growth, so make sure they are getting enough! If you need a quick nitrogen boost and don’t have time to worry about long-term fixes, you can use bat guano or compost to help improve the plant’s health.
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.
Tip: make sure to download my free Grow Bible for more information
While not as common as nitrogen deficiencies, phosphorus deficiencies are a definite possibility, especially in hydroponics systems. 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 essential nutrient during your plant’s flowering phase. In fact, many would say that phosphorus is actually most important during the flowering phase of growth. If your plant lacks phosphorus during the flowering phase, you will limit the potential yield. 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 frailer and lacking life. The initial symptoms of a phosphorus deficiency are darkening foliage and slowing growth. The leaves’ edges on your cannabis plant will lose their vibrant green color – they may even turn brown – and will start to curl in. Other plant parts like petioles will also darken, possibly becoming more blue or red., but it also adds structural strength to the roots and stems of the plant.
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 a higher ratio of phosphorus than whatever you were using before. As long as the N-P-K ratio exceeds 5, the substance will be helpful for your plant’s phosphorus deficiency. Fertilizers developed explicitly for the flowering phase work well, as does bat guano. Water-soluble fertilizers will be your best option for maximum efficiency and ease of use.
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.
Bone meal, 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.
Potassium deficiencies are relatively common in the world of marijuana growing. This is because, with most fertilizers, potassium occurs in the lowest ratios. Compared to the other macronutrients, less potassium is required by the plant.
However, just like the other two nutrients of the primary three, potassium is vital 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
A potassium deficiency has unusual symptoms: the plant might grow taller more quickly and look healthy at first but keep an eye on the lower foliage. If the plant doesn’t have enough potassium, the leaves can turn brown and begin to die. Ultimately, this will slow your marijuana plants’ growth and development.
Indeed, 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 wholly yellow and die. One of the most harmful effects of a potassium deficiency is that your flowering phase would be delayed, leading to a disappointing yield.
You also might notice areas where growth slows or becomes irregular. Remember that potassium is very important to the transfer of water and other nutrients throughout the plant. This means that if you have a substantial deficiency, it can affect the health of the whole plant.
Different symptoms will occur if your plant has potassium toxicity; the edges will begin to yellow, then the tips will brown, and finally, there may be some spotting, very yellow edges, and curling over of the leaves.
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). You can try adjusting the fertilizer mix you are using or add a water-soluble potassium additive as well. 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.
The big three: macronutrients
Although the big three macronutrients are the easiest to identify and are the most common deficiencies, advanced growers, in particular, are going to want to know about the rarer deficiencies that could affect their marijuana plants. There are tons of nutrients to consider altogether, so keep reading for some helpful tips.
The purpose of magnesium is to encourage strong, healthy veins and stimulus on the creation of marijuana leaves. It also plays a role in producing chlorophyll and breaking down enzymes.
Magnesium deficiencies are a relatively rare occurrence for outdoor growers of cannabis, but it’s found indoors and with hydroponics systems. Usually, it will affect the lowest leaves of the plant at the beginning, causing them to yellow and weaken. Although it rarely occurs when growing outdoors, a magnesium deficiency can happen in any plant medium and hydroponic system.
When signs of deficiency occur if must be dealt with quickly or else it will become a major problem causing the plant to quickly lose many of its lower leaves. Magnesium is a nutrient that can move around so the plant can move it from the old leaves to new ones. This explains why magnesium deficiency has a tendency to show up towards the bottom of the plant and on the older leaves. Left unchecked, the leaves will die.
This deficiency can also work its way up the plant from bottom to top until it reaches the crown. Magnesium is a crucial element for the development of chlorophyll in the cannabis plant, so don’t let the problem worsen, especially in the early stages of growth.
The easiest and most common way to fix a magnesium deficiency is the application of Epsom salts. Be careful, though, you want to make sure you’ve diagnosed the deficiency correctly before trying to fix it. If you apply too many unneeded nutrients, you could be causing a whole new problem instead of fixing the real issue.
Signs of a magnesium deficiency
Symptoms begin in the lower leaves when they start to turn yellow and show chlorosis. The leaves start turning inward and will soon die. The outlining of the leaves will feel dry and brittle. The deficiency will move up to the middle and upper half of the leaf, and the growing shoots will start going from pale green to white. All of the petioles and stems will also become purple in color.
Sometimes you may notice light brown spotting on the edges if the issue continues to worsen, even though it is possible this could be a little bit of another deficiency that comes along with magnesium deficiency.
One surprising symptom that some growers notice is the development of red stems on their marijuana plants. If you see your plants starting to have stems that are red in color, you can be sure that it is due to a magnesium deficiency. Try to fix the problem with something such as Epsom salts (see below), but even more importantly, test the pH levels of the soil and the runoff. No amount of Epsom salts will help unless the pH levels are balanced.
You can easily avoid and solve magnesium deficiencies once you are aware of how to handle it. We will go into more detail about this below.
How to fix a magnesium deficiency
There are several ways to resolve magnesium deficiency, but one of the better options is a product called Bergman’s Plant Booster. This is one is very popular because it enhances the quality of your yields and provides a good balance of nutrients.
More options are:
- Dolomite lime
- Magnesium sulfate
- Garden lime
- Worm castings
- Epsom salts
Since both Epsom salt and Magnesium sulfate (wiki) are water soluble, they work the best. For hydroponics systems, Epsom salts are by far the simplest solution. For every gallon of water in your tank add a teaspoon of Epsom salts. Give it a quarter of the initial dosage for every consecutive treatment. If you like, you can even add Calcium-Magnesium (available at this link for only $20)
Tip: make sure to download my free Grow Bible for more information
Magnesium and pH levels
If the pH of your plant’s roots drops too low, the marijuana plant could display signs of magnesium deficiency, even more so in hydro (check these hydro ph levels). This occurs as a result of the pH of the roots not being at the right ratio, which causes the plant to fail to receive magnesium properly from the roots.
Usually, with this deficiency, the magnesium is there, but the roots are not able to receive the magnesium efficiently because of the wrong pH. This is why it is necessary to keep the right pH – to prevent magnesium deficiency.
Providing additional magnesium to a system that has a pH lock-out will most likely not help since the plant can’t take in any magnesium until the pH is made right. If your plant has plenty of magnesium, giving it more could result in the development of other deficiencies by shutting out other nutrients the plant needs.
If you’re growing marijuana in soil, magnesium is better received by the roots in the 6.0 – 7.0 pH rate. If you’re growing marijuana in hydro, magnesium is better absorbed when the roots have a pH of 6.0 – 6.5.
If suspicion sets in and you begin thinking you plant has a magnesium deficiency, flush the system with pure, pH’d water that has a normal dose of marijuana-friendly nutrients in it (including magnesium). This will remove all nutrient salts that may have damaged the plant’s ability to absorb magnesium and help replenish the pH to the right ratio.
Read the article How to rinse a hydro system for more information about flushing.
One of the rarer deficiencies is boron. It’s not common for cannabis cultivation, but it can certainly damage the plant’s potential growth. The most visible signs of boron deficiency are when the growing tips of the plant begin to turn brown or gray.
The growth itself will slow significantly or stop if there isn’t enough boron. In addition to the damage experienced by the growing tips, the leaves may start to develop dead spots. They will be small and scattered and might go easily unnoticed.
Make sure you take counteractive measures to fix boron deficiencies right away. Fixing the problem usually starts with adjusting irrigation processes and making sure you’re getting the boron back into the environment. Boric acid is a simple and common choice for growers, but compost and natural mixes are also potential options to bring the levels back to normal. Read more about boron deficiencies in marijuana plants.
Calcium deficiencies are relatively uncommon for outdoor growers but are not uncommon for indoor growing and users of hydroponics systems. Some areas also have water supplies which don’t contain calcium, and if growers don’t add calcium to their irrigation reservoirs, there likely won’t be enough for the plants to thrive.
Additionally, if you’re growing in a hydroponics system and you’re only using water and nutrients in a solution, then you might be missing a good source of calcium. Calcium deficiencies will usually display symptoms of big dead patches on unusually dark leaves.
The symptoms of calcium deficiencies will usually first arise in the older growth. Branches may become weakened significantly, and any additional weight or stress could cause them to crack or break off. If you don’t address a calcium deficiency early, the plant may also develop some issues in the root systems. Thankfully, treating a calcium deficiency is usually a pretty simple process. Growers often use lime, applying it to the soil or substrate and letting the plant take it from there. Read more about calcium deficiencies in marijuana plants.
Copper deficiencies in cannabis plants are relatively uncommon, but they can cause a lot of damage to new growth. The initial symptoms will be necrosis of the plant matter in young leaves. This will cause the leaves to look brownish or blue-gray at the tips. The new leaves, flowers and other new growth on the plant can also come in limp and weak if there isn’t enough copper.
Since copper is easily renewed in the plant’s environment and is very important for letting the plant thrive and mature, you need to make sure you do your part. Many fungicides contain copper, but there are other options, too. We’ll cover more of your copper options farther along. Read more about copper deficiencies in marijuana plants.
Iron deficiencies are not uncommon for cannabis plants. The first area growers will see evidence of an iron deficiency will be in the new growth of the plant, especially the leaves. The upper leaves will usually be the most affected, becoming discolored and yellowing distinctively.
The veins of the leaf will remain green, but the leaf itself just won’t have enough chlorophyll if the plant has an iron deficiency. Iron holds a vital role in the production of chlorophyll in cannabis plants.
Beware: an iron deficiency and a magnesium deficiency can look very similar to one another. The main difference is that an iron deficiency will primarily affect new growth on the plant. That means the top leaves will be affected far more than those at the bottom and middle of the plant.
Iron deficiencies often occur at the same time as improper pH levels, so you’ll need to take that into account. It’s also common for iron deficiencies to occur in conjunction with manganese and zinc deficiencies, so keep an eye out for those. Read how to treat iron deficiencies in marijuana plants.
Manganese deficiencies are also relatively uncommon in cannabis cultivation. You’ll usually find them occurring in tandem with zinc and iron deficiencies, so remember to carefully test and analyze your plant’s environment when treating them.
A manganese deficiency will display symptoms in new growth, primarily in the leaves. The leaves will develop dead spots and begin to yellow. On the other hand, too much manganese can inhibit nutrient absorption and cause iron deficiencies.
Manganese is a vital element for the creation of chlorophyll and the production of nitrates. Make sure you have plenty of manganese in your nutrient solution or plant substrate. Getting manganese in a water-soluble form is always a good idea since it simplifies the application process. Many growers also prefer compost or greensand. Read more about manganese deficiencies in marijuana plants.
Molybdenum deficiencies are very uncommon, but if they do occur, they will cause some unpredictable and negative effects on your cannabis plant. Without enough molybdenum, the plant’s middle leaves will begin to yellow, and any new foliage will grow out warped or stop growing entirely.
The shoots will begin to curl, and the leaves can develop a strange crimson hue at the tips. Molybdenum aids primarily in the development and production of ammonia for the plant.
One of the main reasons why molybdenum deficiencies are so uncommon in cannabis plants is the tiny amount required. Plants don’t need very much molybdenum. That also means that you should show restraint when treating a molybdenum deficiency. Growers often favor sprays and infused solutions to treat the plant. Read more about molybdenum deficiencies in marijuana plants.
Silicon deficiencies almost never occur in outdoor growing but are always possible in controlled indoor environments. Silicon itself is usually highly abundant in nature, as well as being well represented in fertilizers and nutrient solutions.
Silicon is necessary for plant production in general, so a deficiency will cause the branches and stems of your plant to become weaker than they should be, and the photosynthesis process may be inhibited. Silicon also deters insects and pests; you might notice that you have more issues with insects if your plant has a silicon deficiency.
To treat a silicon deficiency, growers have a number of different options. Many growers favor diatomaceous earth or liquid silicon. Just remember that silicon deficiencies are rare, and it’s always a good idea to check other causes before trying to add more silicon. Read more about silicon deficiencies in marijuana plants.
Sulfur deficiencies don’t occur too often since most fertilizers will have the requisite amount of sulfur already present. Symptoms of a deficiency include yellowing of new and developing foliage, as well as stunted growth.
The new leaves may also be narrower and more brittle than they should be. Sulfur plays an essential role in a number of different vital processes, including chlorophyll development and root system growth.
Despite the moderately small amount of zinc required in the cannabis plant, zinc deficiencies occur fairly regularly. Symptoms of a zinc deficiency include twisted foliage growth and yellowing of the veins of the older leaves.
It’s also possible for the plant to begin to lose color and grow paler. When the flowering phase occurs, the same issue can crop up in the buds, and they might curl or become deformed. Zinc deficiencies often occur in tandem with iron or manganese deficiencies.
Zinc plays an essential role in many different plant processes, including plant development and the production of vital enzymes. Severe deficiencies can cause the plant to wilt or even break the stem. Because of the linkage between zinc, manganese, and iron, it’s important to be careful when trying to treat a zinc deficiency. Read more about zinc deficiencies in marijuana plants.
Getting your plants back to health
If you properly resolve a deficiency issue, the yellowing and discoloration of the leaves should cease almost instantly. Some damaged leaves could bounce back to a certain extent, but what matters the most is that you ensure the issue is not still spreading to the other leaves on the plant.
We suggest not getting rid of the discolored leaves until you are confident the issue is resolved entirely and is not spreading to the newer leaves. It is better if any continued discoloration occurs on the leaves that were already damaged.
Once the issue is resolved, damaged leaves can be removed when they are almost completely discolored, and maybe a little sooner. Prune lightly when you do so that you do not stress the plant any further. Assuming they aren’t discolored, make sure to leave your fan leaves intact because they are absolutely crucial to the health of your plants. This is even the case if there is a heat wave.
Remember, pay close attention to the growth of your plant. If you suspect any issues, use the list of symptoms to determine if there is a deficiency. No matter what type of deficiency your plants had, the new growth will really show you whether they are improving or not. Once you have followed the proper steps to restore balance, remember that it may take a few days before the deficiency is completely cleared up.
If the idea of a deficiency concerns you, lower your risk by starting with great seeds. Plants with strong genetics have less chance of getting sick. Make sure you buy marijuana seeds from a trusted seed bank.
The founder of I Love Growing Marijuana, Robert Bergman, is a marijuana growing expert that enjoys sharing his knowledge with the world. He combines years of experience, ranging from small-scale grows to massive operations, with a passion for growing. His articles include tutorials on growing... [read more]