Are You Killing Your Cannabis Plants?!d

Knowing what’s wrong and how to fix it

There is nothing more frustrating than growing cannabis, and having it die on you. There are many things that can straight up “murder” your plants, and today we’re going to be going over some of the more common issues.

There’s a lot to cover, so we will just jump right into it.


Insect pests can be many and varied, and although not all are 100% fatal to the plant, many of them are capable of devastating our garden if they’re not treated properly. Of course, it’s always possible that the plant will survive the infestation, but a serious insect attack will almost always lead to weak plants and lower yields.

What makes cannabis pests such a hassle is that there are many of them. Some more versatile than others.

The most common type of pests you’d run into are:

  • Aphids
  • Spider Mites
  • Thrips
  • Broad Mites

To name a few. There is a more extensive list that you can find here.

At times, a pest infestation could be mistaken for other issues such as overwatering, nutrient burn or heat exposure. However, once you realize that it’s actually the result of little bugs having orgies on your plants – it might be too late.

If you’re in the flowering cycle, it’s important to know when to use pesticides and when not to. Also, the type of pesticide is important. During the vegetative stage of the plant cycle you’ll have more leeway to use pesticides as it will degrade before the flowering cycle. If you do happen to use pesticides during the flowering cycle, it’s important to use organic and non-toxic pesticides and to properly flush your plant.

Overwatering, Nutrient Burn, Drought and other human errors

Growing cannabis is an art and you’ll need to treat your plants with attention and care.

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The most common cause, especially among beginner growers, is undoubtedly overwatering. The excess of irrigation particularly affects young plants in their first weeks of life (although it can also occur with larger plants).

The main reason is watering too much, too frequently. Small plants have a very limited resistance, partly because of their size. A plant with two cotyledons and three small roots can not cope with large amounts of water, simply because they can not process it, not having sufficient absorption capacity in the root zone.

In terms of overwatering you simply need to know how fast your plant consumes water.

In hydroponic systems, this usually isn’t a problem. However, in soil, you simply have to press your finger into the soil (about an inch deep) and feel if it’s moist. If the soil is moist, you don’t need to water. If it’s dry…obviously it’s time for watering.

Nutrient burn

Organic fertilisers don’t tend to over-fertilise plants because they release nutrients slowly. If using mineral fertilisers for cannabis, this possible problem must be taken into account if we want to avoid problems.

To find out if the substrate has an excess of mineral salts, we need to monitor the EC of the drainage water. If the runoff comes out with a similar EC to the inlet (the one used for irrigation) then everything is correct. However, if the EC of the drainage water is much higher than the inlet water, a root-flush should be performed to wash the excess salts out of the substrate. Using enzymes in each irrigation helps keep the substrate free of salts.

For instance, during the flowering cycle the plant will increase its nutrient uptake and perhaps you would need to add some more.

During the vegetative stage, you should not be adding more nutrients (in soil). This is especially true if you properly prepared your soil beforehand.


A lack of water, or drought stress is another of the principal factors that can seriously affect plants and cause premature death. The plants require water for their survival, and if they run out of it for a few days or even hours (depending on the cultivation system) they can die very easily.

Even if the plant manages to survive the drought period, it’s inevitable that part of the root system will be affected. When part of the root system dries out and dies, it is usually accompanied by some of the leaves and branches, which will weaken the plant and reduce it’s capacity to process nutrients, impacting negatively on development and translating into a smaller final harvest. If this period of drought is repeated or is too prolonged, the plant may not be able to survive as well it could the last time, as its root system is now much less extensive than it was initially. Remember that you can use products to stimulate root growth, helping the plant to develop more roots and therefore feed more efficiently and more able to tolerate any periods of drought.

Growing cannabis will have a learning curve, and over time you’ll become more familiar with plant dynamics. Every good grower has a few cannabis skeletons in their closet. The trick is to identify where you went wrong and to learn from your mistakes.

Rot, Mold and Fungus

The grow environment is incredibly important. I prefer to work in sterile environments, but sometimes that isn’t possible. Nonetheless, it’s important to keep your grow area well ventilated and to not have water stagnate.

Root Rot can occur when the water stagnates and usually is more of a problem for people growing in deep water cultures. Essentially, it becomes a breeding ground for organisms that will rot away your roots ultimately killing your plants.

It’s important to keep the water moving and to ensure that it’s getting oxygen.

Mold also occurs when there is too much humidity and stagnation in the airflow. Be sure to maintain the optimal humidity within the grow and keep it well ventilated. Not only will the breeze help make the plant stronger, it will also help keep certain pests at bay (like Spider Mites). Always have a fan blowing on your grows.

This will help stop the development of fungus as well.

The truth of the matter is that at one point in time, you’ll run into a problem when growing cannabis. If you lose a plant – it sucks. However, it can also be a great learning experience allowing you to become better at the art of growing the sticky icky.

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