Common Problems When Growing Cannabis

Common Problems When Growing Cannabis

When you first start growing, it can be very overwhelming. There are so many factors to take into consideration. It’s exciting and scary at the same time. You’re scared of messing something up but excited about growing your own cannabis. Both the fear and excitement can cause you to do things that may cause stress to the plant. There are some common problems when growing cannabis. Luckily, I am here to tell you what those things are and how to avoid doing them.

Over-Watering, Under-Watering & Incorrect pH Range


The number one mistake new growers make is over-watering their plants. We get this idea in our head that the plants need water every single day to grow. While that can be true in some cases, it’s not usually the case. If you over-saturate the soil, the plants roots cannot get oxygen, which is needed for healthy root development. The healthier the roots, the easier it is for them to do their job of absorbing nutrients and water. You want to let your growing medium dry out in between watering, so that the roots get both water and oxygen. An over-watered plant will have leaves curled downward and look very rigid because they’re full of water. Growth will slow down and if not fixed, can lead to root rot. If you over-watered your plant, let it dry out for a few days and then resume a more appropriate watering schedule.


Although more rare, some growers will underwater their plants. After hearing over-watering is the most common mistake, many new growers end up under-watering for fear of over-watering. If you have an under-watered plant, the leaves with droop and seem like they’re hanging. They may also appear thin like paper. To fix this problem is easy, just water you plant. But be sure to start with a smaller amount than usual as to not shock the plant. Once it perks up, you can give it the rest. After that, try watering more frequently.

As a seedling, plants don’t need much water, so try watering in a small circle around the stem. By doing this, rather than saturating the entire growing medium in the pot, you minimize the chance of over-watering. As the plant gets bigger, so can the circle of water. Keep enlarging the watering circle until the plant is about 8 inches tall. Once it gets to that height, water the entire medium until you see a tiny bit of run off in the tray. You can water about every other day, but monitor the top 1 inch of medium to assess the moisture in it. Once plants get bigger, so does their thirst for water.

Incorrect pH Range

Providing the correct pH range for your plant is so crucial to its health. It is one of the most common reason growers experience problems with their plants. So always check your runoff first to assess if your pH levels are correct. If the pH is not in the correct range, the plant can’t absorb all of the nutrients it needs to grow.

Different nutrients absorb at different pH values. For example in soil, nitrogen is absorbed at a pH range of about 5.5 to 7.5 but phosphorus is absorbed in the range of 6.0 to 7.0. This is why the pH for each medium has a range. Within that range, all nutrients are able to absorb through the roots. So, when you give a variety of pH to your plant, it can absorb certain nutrients more efficiently than at different times. This will help your plant to be its healthiest, which means faster growth.

Ideal pH ranges:

  • Soil – 6.0-7.0
  • Hydro/Soilless mediums – 5.5-6.5

For more information on how to pH balance your water, check out my post, The importance of pH levels for your plants

Nutrient Burn & Nitrogen Deficiency/Toxicity

Nutrient Burn

Another common mistake made by first time growers is nutrient burn. This is because we want to get the best results and become a little too enthusiast with the nutrients. They either feed too much at once or too frequently. When giving plants nutrients, it’s always a better idea to start out smaller and increase it slowly. It’s much harder to get nutrient burn when using organics and living soils because you’re feeding the soil, not the roots directly. Plus, it’s a slow release of nutrients to the roots. Autoflowers require much less nutrients then photoperiod plants, so make sure not to give your autoflower a nutrient feeding designed for a photoperiod plant.

Nutrient burn will cause yellow then brown, crispy looking edges on the leaves. It will also slow down growth. The leaf tips will be affected first. So, keep your eye out for the leaf tips first. If you have nutrient burn on your plants, stop feedings for a 1-3 weeks depending on how bad the burn is and then resume a more suitable feeding schedule. This will allow the plant to flush out the large amount of nutrients.

Nitrogen Deficiency & Toxicity

Nitrogen is one of three main macronutrients that cannabis plants need for proper growth. When you buy any fertilizer/nutrient, they have a N-P-K ratio on the package. These stand for: Nitrogen, Phosphorus and Potassium (K on periodic table). Nitrogen is needed most in vegetation, but important for the plant throughout its life.

If the plant doesn’t get enough nitrogen, the leaves will start to turn bright yellow and die. Towards the end of flower, this will happen naturally as the plant uses the last the nitrogen in its system. This can be easily fixed by adding some nutrients with a high N amount in the N-P-K ratio at the recommended dosage.

Nitrogen toxicity is caused by too much nitrogen in the plants system. This is also referred to as ‘the claw’ as it causes the end of the leaves to curl downward in a claw like fashion. The leaves will also turn a dark green. If you see these signs, let up on the amount of nitrogen in your nutrient feedings. For more information on nutrient deficiencies, check out my blog post, What are mobile & immobile nutrients?

Heat Stress & Light Burn

Heat Stress

Stress your plant experiences from the grow room being too hot is called heat stress. Aim to keep your temperature between 70-75°F/21°-24°C during vegetation. You can make it a little cooler every 1-2 weeks during flower to simulate fall. If it’s too hot for your plant, the leaves will fold up long ways or ‘taco’. If you suspect your plant is experiencing heat stress, try lowering the temperature. This should alleviate the symptoms of heat stress.

Light Burn

If your plant tops are too close to your light, they will get light burn. The very tops of the plants will yellow first, and then it will spread. It can also cause pale, white bud tops if not corrected. If light burn is present, raise your light about 6 inches to 12 inches. Remember to always read your manual for your light for specifics for light height during different stages of growth. If your plant is experiencing heat stress, it is more likely to suffer from light burns.

White Powdery Mildew & Bud Rot

White Powdery Mildew

One of the most common types of fungi your cannabis plants can get. Often caused by too much humidity in the grow room and little to no airflow. You will see a powdery substance appear on your leaves and it can spread to other plants in your grow area. It is a form of mold that can affect your cannabis plant. To get rid of it, simply spray plants with mildew eliminating spray. Also, lower humidity and increase airflow to prevent it from coming back.

Bud Rot

Another problem caused by high humidity and poor airflow. Bud rot is exactly what it says; your buds basically rot from the inside out. The rotting is caused by another type of mold that can affect your cannabis plant. It can be very difficult to identify early on. Bud rot starts at the stem and spreads in all directions. It starts as white and wispy, then grey and black as the buds become a mushy, slimy consistency. If bud rot is present, it’s no longer safe for consumption. It needs to be removed from the plant and disposed of or the entire plant may need to dispose of. This depends on the severity of the bud rot. Prevention is the best treatment for bud rot. Maintain a constant movement of air and keep the humidity at around 50-55% to avoid issues.

Spider Mites and Aphids

Spider Mites

Although not as common as some of this list, spider mites are harder to deal with. If you don’t find them early enough, there’s a chance you won’t be able to get rid of them. They hide on the underside of the leaves. They cannot be seen very will with the naked eye so you’ll have to use a trichome scope or some sort of magnifier to view them.

The mites look like tiny spiders, hence the name. The early signs are tiny, light coloured spots on the leaves and as it progresses, you’ll see what looks like spider webs covering the leaves and plant. By the time you see the webs, it’s usually too late. If you catch them early on, you can get some ladybugs to add to your plants and they’ll eat them fairly quickly. The mites reproduce rapidly so make sure to get them all or they will return to cause issues again.


Aphids are another bug that can affect your plants. You can also find them on the underside of the leaves. They look more like a tiny green grasshopper with long legs. You’ll need to view them under a magnifier like the spider mites. They suck the water and nutrients out of the leaves, which causes them to wilt and die. If you don’t catch them quickly, they can kill a lot of leaves on your plant. You can spray your plant with a neem oil if it’s not in flower, but i wouldn’t recommend spraying plants that have started flowering. The neem oil is an all natural insecticide. You can also add ladybugs to your plants for aphids as well. They love eating aphids so just add them to the plant and they’ll take care of the rest.

You can buy ladybugs at your local garden stores or online. For Canadians, you can buy 250 for $18CAD from You can also try your local garden supply stores.

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