How To Deal With Slow Cannabis Growth

Created by
Added 21 October 2020

How To Deal With Slow Cannabis Growth

If you have noticed your cannabis plant's growth rate declining, there could be something wrong with it. From pH problems to issues with the roots, there are many reasons why your cannabis plant might be slowing down. But how do you deal with slow growth? This article goes over the possible issues related to sluggish plants so you can get your babies back on track in a flash.

Are You Being Impatient?

The first thing to ask yourself is, 'am I being patient enough?'. There have been too many cases where growers drastically try to fix problems that aren't even there and end up making them worse. With all the different issues a cannabis plant can face, incorrectly treating a problem is easy to do.

Before doing anything, it is important that the issue is diagnosed correctly so you don't end up slowing your plant down even more.

It might simply be that the strain you are growing is just a slow producer. Slow growth does not necessarily mean your plant needs a boost on the feeding front. This is probably the most common error beginners make when their cannabis plants are growing slowly. It is better to take a step back rather than go into full problem solving mode. Understanding why your plants are slowing down is the first step towards speeding them up again.

Slow Cannabis Growth

The slow growth in a cannabis plant is often accompanied by other changes, such as deformed or discoloured leaves, but it is usually the first indication that there is a problem. It can be a challenge spot early unless you are monitoring (and measuring) your plants everyday. Eventually, a cannabis plant will completely stop growing if the problem becomes severe.

Why Is My Cannabis Plant Growing Slowly?

Slow growth is caused by a number of affecting factors. Remember, we are in charge of providing our plants with basically everything they need to grow healthy. So, any slow growth is likely to do with an imbalance somewhere, either with the feeding or watering, or the conditions the plants are being grown in. As we mentioned already, genetics do also play a role in the growth speed, but the conditions do need to be correct for the plant to reach that potential.

Most of the time slow growth is related to the environment unless you are seeing clear signs of nutrient deficiency. Below we discuss 8 causes of a cannabis plant that isn't growing fast enough.


Overwatered Cannabis Plant

Most growers have probably overwatered their plants at some point thinking it can help to speed things up. Unfortunately, watering too much does the complete opposite. Giving cannabis plants too much water results in stunted growth because the roots essentially become suffocated from lack of oxygen.

Other roots problems begin to emerge from overwatering, such as root rot, nutrient lockout, and problems with pests. Once you have to deal with those, plants may slow down even more and the possible recovery time takes longer.


  • Water only when your plants need it. Make sure you give them a wet and dry cycle by watering less, but more frequently.
  • Pot size should be big enough so that you water at least once every day or two, so the grow medium does not stay wet for extended periods of time.


Underwatered Cannabis Plant

Water is a basic requirement for most living organisms. It is fair to say that when a human being is dehydrated, their productivity and body functions slow down. The same could be said for cannabis plants. Apart from slow growth, not giving providing enough water can bring a whole different set of problems, and could potentially be fatal for a cannabis plant.

Underwatering results in shrivelled, wilting plants that cannot support themselves. When a cannabis plant experiences complete drought, capillary hairs on the roots start to dry out and die, which seriously stunts plant development. A cannabis is unlikely to recover from heavy damage caused by underwatering, especially in hydroponics and aeroponics systems.


  • Give your plants pH corrected water until you see runoff draining from the bottom of the pots. Wait until the grow medium is nearly dry before feeding again. 
  • Add amendments to your grow medium to prevent too much water draining or evaporating. Coco coir, clay pebbles, and vermiculite all work well to retain water.

Nutrient Deficiencies

Optimum pH Levels For Nutrient Absorption

A cannabis plant needs certain nutrients in order to grow properly. Most of the soil mixes available on the market for cannabis contain enough nutrients for the first few weeks. If the conditions are correct, there should be no issues with the speed of growth. Eventually, growers will have to add fertilizer if they are looking to maximise health and achieve optimum yields. Without the right nutrient levels, a cannabis plant can become deficient.

If deficiencies occur, then it is likely the plant will stop growing as vigorously. You'll notice deficiency symptoms mainly through the leaves, in addition to an overall decline in health.


  • Correct the pH and EC of your feeding solution. Most of the problems related to nutrients are caused by pH.
  • Store bought nutrients are often heavily concentrated and should be diluted. It can happen that deficiencies arise because of overfeeding.

Over/Under Exposure To Light

Light Deficiency In Cannabis Plants

Cannabis plants need a lot of light, but too much may be stressful. It could be that your plants are growing slowly because they are being overly exposed to light. On the other hand, they could not be getting enough. Either way, you need to make a change to your setup if you want to prevent your plants from lagging behind. 


  • Move your lights closer/further away from the canopy.
  • Consider increasing the wattage of your lights to increase growth rates.

Incorrect Spectrum

Make sure you think about the spectrum of light your plants are receiving during the different stages of growth. Many grow lights nowadays have the spectrum necessary for the entire grow cycle. Some are designed for vegetation and will emit more blue wavelengths, and others give out a reddish light, which work well for flowering.

Giving your plants the correct spectrum allows them to grow strong and healthy. Without the right wavelengths, they can slow down. Get it right, and your plants will love you for it.


  • Invest in high quality lights suited to each stage of growth.
  • Check their wattage and colour spectrum.

PH Problems

An imbalanced pH is one of the leading causes of slow cannabis plants. Not maintaining the right levels leaves you with lots of other issues, like root problems and nutrient deficiencies. Keeping a stable pH within the correct range means your plants can absorb minerals efficiently and grow rapidly because of it.


  • Use a digital pH meter to measure runoff or feeding solution.
  • Keep your soil between pH 6 - 7, and your hydroponics system at pH 5.5 - 6.5.

High/Low Temperatures

Temperature has a big effect on how cannabis plants function. Some strains prefer slightly higher temperatures than others, so if you are noticing slow growth, be sure to check your hygrometer to see if it has fallen out of the comfortable range. Don't forget that humidity can also be a culprit and is well tied to temperature. 

Temperature and Humidity Levels For Cannabis Grow Room


  • Install ventilation and place oscillating fans around your grow area.
  • Maintain proper humidity levels.
  • Heaters or airconditioning can be used in harsher climates to maintain temperature.

Pests and Fungus

Cannabis Pests

In the unfortunate event that your garden gets infested with unwanted guests, you may have to deal with slow plants that need plenty of time to recover. Pests and fungus can massively affect cannabis plants to the point where they cannot be saved, let alone recover from slowed growth. It is extra important that the grow space is kept extremely clean to that pests don't have a chance to get a foothold.


  • Regularly clean and disinfect grow space. Do a thorough clean between each grow.
  • Maintain the correct temperature and humidity, as well as provide adequate ventilation. 


As you've probably realised by now, slow plants can be the result of many different mistakes. Try to keep a proper schedule and monitor your plants regularly so you can catch any signs of unhealthy growth. The sooner you spot the problem, the quicker you can find a solution to get your plants in tip top shape. 

White Widow by Powderfinger from GrowDiaries.

External References

Effects of Acidity on Mineralization: pH-dependence of Organic Matter Mineralization in Weakly Acidic Soils. Soil Biology and Biochemistry. - Curtin, Denis & Campbell, C. & Jalil, Abdul. (1998).

Effect of Irrigation and Fertilization Levels on Mineral Composition of Cannabis sativa L. Leaves. Notulae Botanicae Horti Agrobotanici Cluj-Napoca. - Wogiatzi, Eleni & Gougoulias, Nikolaos & Giannoulis, Kyriakos & Kamvoukou, Christina-Anna. (2019). 

This article was updated October 2020.


Be the first to comment it