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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.
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.
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