Cannabis Nutrient Deficiencies: Telltale Signs

Cultivating cannabis can be a double-edged sword. On one hand, it can be one of the most rewarding things that you will ever do. On the other hand, many of the common cannabis plant deficiencies can make growing marijuana one of the most frustrating things you will ever do.

It is nearly impossible to refrain from getting emotionally invested in a cannabis garden. That is also true regarding the financial investment. So when things go wrong in a garden, no matter the size of the operation, it can be soul crushing.

Every true cannabis cultivation expert will be quick to point out that no matter how much knowledge they have accumulated or how many successful crops they have harvested, they still run into problems from time to time.

The fact of the matter is that the cannabis plant can be finicky with hurdles and issues popping up during the cultivation process. One very common problem is cannabis nutrient deficiencies. Marijuana plant deficiencies come in many forms, knowing how to spot them and how to fix them is crucial to success.

It is a virtual guarantee that if you cultivate long enough, you will run into nutrient deficiencies. Educating yourself on common types of cannabis nutrient deficiencies and being prepared ahead of time very well could be the difference between you salvaging your harvest or having no harvest at all.

The Green Flower team, in conjunction with nutrient expert Simon Hart of Grotek Nutrients, has identified some of the most common types of cannabis plant nutrient deficiencies. In this article, we will discuss their deficiency symptoms and how to properly address each type of problem you’ll likely encounter. 

However, first we will discuss some very important factors to keep in mind when it comes to cannabis plant nutrient deficiencies.

Is It Really A Nutrient Deficiency?

It is very common for a cannabis cultivator to see a cannabis plant that looks unhealthy and assume that cannabis nutrient deficiencies are to blame. That is especially true for beginner cannabis cultivators who are seeing a struggling cannabis plant for the first time.

However, just because a cannabis plant looks unhealthy does not necessarily mean that it is lacking proper nutrients. It is possible that the plant could be experiencing health woes due to something else such as a bug infestation or a temperature issue.

Even if other factors can be confidently ruled out, it is still possible that it’s not the nutrients themselves that are the cause of the issue. It’s quite possible that the cultivator is feeding their plants the right amount of nutrients yet the marijuana plants are not absorbing them properly due to one or more reasons.

Nutrient Uptake

When a cannabis plant is fed, the plant’s roots absorb nutrients from the moisture and grow medium, or in cases of hydroponics, the water that the roots are suspended in. In layman’s terms, the roots eat the nutrients and get them to where they need to go throughout the plant via a process known as nutrient uptake.

Several factors affect a cannabis plant’s nutrient uptake potential. For example, the pH level of the water that the roots are feeding from will have a direct impact on the plant’s nutrient uptake capabilities. Cannabis plants prefer water that is as close to 7 pH (neutral) as possible. If the pH deviates a small amount from that level, either above or below, it can essentially limit the amount of nutrients that a cannabis plant can absorb.

The amount of water that the plants are being fed is another factor that can affect nutrient uptake. If a cannabis plant is not being fed enough water, it won’t be able to absorb enough nutrients. Conversely, if a cannabis plant is being watered too often, it won’t be able to absorb enough nutrients.

Combining certain nutrients and using them at the same time to feed plants can lead to nutrient uptake deficiencies in cannabis plants as well. Some nutrients effectively cancel each other out when mixed together, and that’s a common issue that arises when inexperienced cultivators make their own nutrient mixes.

In any of the above scenarios the cultivator will have seemingly fed their cannabis plant(s) the right amount of nutrients, yet their plants will appear to be experiencing cannabis nutrient deficiencies and limited plant growth. The ancillary factors will need to be addressed first, otherwise no change in nutrient feeding levels will fix the actual underlying problem(s).

Early Intervention & Frequent Monitoring

If a cultivator can confidently determine that it is indeed a nutrient deficiency or deficiencies that they are dealing with and that it’s not some other type of factor, then early intervention is extremely important. If a plant is truly experiencing one or more nutrient deficiencies it does not take long for the plant to be harmed to the point that it cannot be salvaged.

One of the most important things that every cannabis cultivator can do is a daily visual inspection. It is likely that many cannabis cultivators stare at their plants probably more than they should, however, many make the mistake of not inspecting their plants often enough. Whether it’s bugs, temperature, disease, some type of equipment malfunction, or nutrient deficiencies, it does not take long for a cannabis garden to be ruined, which is why constant monitoring and early intervention is key.

Make it a point to start every garden day with a thorough visual inspection of every part of every cannabis plant in the garden. Pay close attention to the bottoms of every leaf, and pay special attention to the older leaves. Obviously, you want to keep green leaves in place, however, if you see leaves that look like they are dying or look noticeably unhealthy, remove them immediately.

Frequently perform as many types of level-based tests as possible — monitor pH levels in the water and soil, EC levels, PPM, total dissolved liquids, and anything else that you can afford to perform tests on. The more types of data that you can acquire the better. It is somewhat common that a leaf is visually showing an issue, yet that issue is not reflected in the soil, water, or tissue testing.

If a plant is experiencing issues, perform as many tests as possible on the cannabis plant to set a baseline, then perform more tests to monitor what is going up and what is going down, and adjust feeding strategies accordingly.

Common Nutrient Deficiencies During The Vegetative Stage

As previously mentioned, the cannabis plant will require different levels of nutrients depending on where it’s at in the growth cycle. Some deficiencies in cannabis plants are more common during the vegetative phase compared to the flowering phase.

Arguably the most common type of nutrient deficiency during the vegetative phase is nitrogen deficiency. The cannabis plant certainly needs more nitrogen during the flowering phase compared to the vegetative phase, however, some growers make the mistake of not giving their plants enough nitrogen during the vegetative phase. A nitrogen deficiency comes in the form of leaves that turn yellow progressively, starting from the bottom of the plant and moving its way upward to the top of the plant. 

Many products exist that can be added to water and fed to cannabis plants to fix a nitrogen deficiency problem. Make sure to proceed with caution when it comes to nitrogen. A little goes a long way and too much nitrogen can quickly kill a cannabis plant. As with all nutrient deficiency adjustments, try to add additional nitrogen to the feeding schedule of one plant and see how it reacts. If it seems to help, then apply the additional nitrogen to the feeding schedule of the other plants.

Magnesium deficiencies are more common during the flowering phase, however, they can occur during the vegetative phase as well. Magnesium deficiencies show on leaves in the form of interveinal yellowing versus the all around yellowing that occurs with a nitrogen deficiency. The easiest way to address a magnesium deficiency is to include more epsom salt in the feeding schedule. 

Epsom salt is particularly useful because it also includes sulfur and helps cultivators fight off sulfur deficiencies. Sulfur deficiencies can occur during the vegetative phase and the flowering phase, and can be hard to differentiate from a magnesium or nitrogen deficiency.

Common Nutrient Deficiencies During The Flowering Stage

In addition to the previously mentioned types of nutrient deficiencies, which can all occur during the flowering phase, several other types of nutrient deficiencies are common during the flowering phase. When a cannabis plant is flowering it requires more nutrients, which is why so many more types of nutrient deficiencies occur during this phase of the plant’s growth cycle.

Iron deficiencies are common during flowering, and can be very hard to differentiate from a magnesium deficiency which is also common in flowering. The best strategy is to boost the use of products that have both nutrients in them because if one type of deficiency is occurring, the other is likely to follow if it isn’t occurring already.

Potassium deficiencies are also common during the flowering phase. A flowering cannabis plant uses a lot of potassium since potassium is what helps the buds swell in size. A potassium deficiency shows itself via the yellowing and ‘burned’ look on the edges of the blades of leaves. Nutrients rich in potassium are easy to find at any gardening store.

Phosphorus deficiencies are fairly rare with cannabis plants, however, they do occur. When older leaves on the plant start to experience brown spotting, or another dark color, and growth has slowed and new leaves are really small, it’s likely due to a phosphorus deficiency. Remove the spotted leaves and boost feeding with a phosphorus-rich nutrient product (they are very common at gardening stores).

Other Types of Cannabis Plant Deficiencies & A Word Of Caution

If you have mitigated issues regarding the previously mentioned types of nutrient deficiencies, you should be fine in your garden pursuits. However, there are a handful of other deficiencies that can occur and that cultivators should be aware of:

  • Zinc deficiencies — younger leaves start yellowing in between veins
  • Calcium deficiencies — younger leaves curl
  • Manganese deficiencies — yellowing leaves and brown spots, often confused with phosphorus deficiencies
  • Copper deficiencies — leaves get dark and shiny

When it comes to cannabis nutrients, more does not always mean better. For starters, cannabis plant nutrients are expensive, and using any more than is required has the same effect as lighting money on fire. Too many nutrients can also kill a cannabis plant, sometimes at an even faster rate than not feeding a cannabis plant enough nutrients.

When cultivators, especially newbies, think that a plant is not receiving enough of a particular nutrient or nutrients, they tend to overcompensate. A very obvious sign that a cannabis plant is being fed too many nutrients is the leaf tips looking like they were burned.

If that is happening with your plant, back off using nutrients and just feed the plant water, and lots of it. Flush cannabis plants with 3-4 times as much water as they normally receive and let as much water pass through the soil and leak out of the bottom of the containers as possible. 

Test the water ‘runoff’ after it passes through the grow medium to see what levels of nutrients are in the runoff. Hold back on feeding the cannabis plant whichever nutrients are off the charts in the runoff water tests until the levels have come back down to normal, and even then, only feed the plants half as much of those particular nutrients for a couple of weeks following the flushing.

One thing that many expert cultivators recommend is using a garden journal and writing down feeding information and plant observations. The journal will help the cultivator spot trends that they may have not noticed otherwise, including over-feeding. It’s all part of the greater effort to boost education and the learning experience. After all, becoming an expert cannabis cultivator is a lifelong, never-ending journey!

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