Cannabis Plants Growing Slow: Top 8 Reasons And How To Fix Them

Have you ever wondered why your cannabis plant is taking its sweet time to grow? It’s time to stop scratching your head and understand why it could be happening. 

There are various reasons, but we have highlighted a few as beginners are prone to make these mistakes. In this article, we take a look at some of the most common reasons why your cannabis plant may be growing slowly, including the use of wrong lights, incorrect pH, small pot size, pests, and much more. Apart from that, you’ll also learn how to fix these problems.

It can be very frustrating if your plant grows too slowly, especially when you see others harvesting in just a few weeks. And, if your harvest is timed with the weather? Well, then, you’ve got to do something before it’s too late. So, go through the potential causes, determine what your plant is facing, and start fixing it. 

1. A Wrong Lighting Setup 

In many ways, growing cannabis is all about getting the right kind of light setup. Every grower worth their buds swear by using the best lights they can get their hands on. Even then, mistakes can happen. 

Unfortunately, light is pretty unforgiving. Your cannabis plant lives on light, and without the right kind of light, your plant will find it difficult to flourish and produce excellent yields. Here are some of the problems you may run into. 

• Inadequate Light

The most common reason why your plant may be growing slowly due to light issues is inadequate light, and this applies to both indoor and outdoor plants. In an outdoor environment, this can happen due to clouds or overcrowding of plants, and indoors, it can happen due to subpar light output. 

A good way to know whether this is the issue is if your plant stretches, too, as a last-ditch effort to get closer to the light source. 

How do you fix this? Stop relying on the light’s wattage and focus on PPFD. PPFD stands for photosynthetic photon flux density, or the amount of photosynthetically active radiation (PAR) light reaching your plant. 

You can measure PPFD with a lux meter, and ideally, you want your grow lights to produce around 300 to 600 μmol in 18 hours during the growth stage and 450 to 900 μmol for 12 hours during bloom. 

• Too Much Light

On the flip side, your cannabis plant may be growing slowly due to too much light. This especially occurs if your cannabis is exposed to sunlight for too long since the heat from the light can slow down your cannabis’ metabolic processes. 

Usually, this problem occurs along with other symptoms of light burn, including yellowish or burnt leaves with green veins. Move your light farther and measure its PPFD. 

• Wrong Light Spectrum 

Apart from that, your cannabis plant may grow slowly if you are giving it the incorrect type of light. Cannabis prefers different wavelengths during different growth stages, so you need to pick the right type of light. 

For seedling and growth stages, give your plant light that is rich in blue color, and during bloom, give it red to far red light. Here, you can use configurable LED lights or switch between MH lights (blue dominant) and HPS lights (red dominant). 

• Improper Light Cycle 

You can have everything nailed down when it comes to light, but if you mess up the light cycle, expect your cannabis plant to throw a tantrum. In severe cases, your plant can even turn into a hermie or start re-vegging — you want to avoid these problems as much as you can as you’re probably looking for seedless or sinsemilla buds that offer maximum potency. You don’t want seeds now, do you?

So, make sure you give your cannabis plant all the light it needs. As long as the distance from the grow light is appropriate, they won’t mind. Also, don’t reduce the number of daylight hours just to save on the bills as you’ll end up with less yield and defeat the purpose of growing buds at home.

2. Improper pH Levels

pH is one of the foundations of a healthy cannabis plant. pH essentially refers to the concentration of hydrogen ions in the nutrient solution or the growing medium, representing its acidity or alkalinity. 

But here’s the tricky part. pH scale is logarithmic, so even small changes lead to major consequences. When the pH strays too far from ideal, the roots find it difficult to absorb nutrients properly, leading to deficiencies and slow growth. 

So, how do you fix this? Get a pH meter. Measure the pH of your nutrient solution to make sure it is between 5.5 to 6.5 if you’re using a hydroponics system and 6 to 7 if you’re growing in soil. That’s not where it ends, though. You also need to measure the runoff water’s pH as well.

If the runoff water’s pH is not the same as the nutrient solution, there is a salt buildup in the growing medium, i.e., the medium’s pH is not ideal. Flush the growing medium with a ton of RO or pH-neutral water and restart with a pH-balanced nutrient solution. 

3. Nutrient Problems 

Your plant may have the best pH, but if the nutrients you give it are not ideal, your plant is in trouble. Such nutrient problems occur in various forms, such as the following. 

• Nutrient Deficiencies 

A nutrient deficiency is when your cannabis plant does not get enough nutrients to sustain its growth. This can happen due to several reasons, including wrong ratios, overwatering, root problems, pH issues, etc. 

Nutrient deficiency is nasty and can present itself with various symptoms, such as:

• Slow growth
• Vigor loss
• Small plant size
• Low potency buds 
• Buds that lack flavor and aroma, etc.

Fortunately, cannabis is very communicative, so you will know about this issue quickly. You then have to start fixing it. How do you do that? Remix your nutrient solution, flush the growing medium to remove excess salts, and water your plant properly. You can also foliar feed your plant to give it a nutrient boost. 

• Nutrient Toxicity or Burn

On the other hand, you can sometimes give your cannabis plant too many nutrients, which can lead to nutrient toxicity or burn. This can happen due to incorrect nutrient ratios, use of chemical fertilizers, bad water quality, improper pH, etc. 

When this occurs, your plant will show symptoms like stunted growth, yellowing leaves, burnt leaf tips, curling leaves, pH imbalance, etc. 

To fix nutrient toxicity or burn, you need to work on the pH of the soil by flushing it, followed by using chelated nutrients and adjusting the feeding regime. 

• Nutrient Lockout 

Nutrient lockout is a cousin to nutrient toxicity, and this occurs if one or more nutrients are present in a high concentration in the soil. This can prevent the roots from absorbing other nutrients. 

This problem presents symptoms similar to nutrient deficiency since your plant cannot take in nutrients, even if they are present in the soil. The nutrients are locked out. 

Here are a few things to keep in mind to deal with and prevent such problems from occurring again:

• Maintain the right pH, depending on whether you’re growing in hydro or soil
• Maintain a PPM level of 500 to 600 for seedlings, 800 to 900 for vegetative plants, and 1000 to 1100 for flowering plants 
• Be conservative when using feeding charts 
• Use products and nutrients specifically made for cannabis plants 
• Choose organic nutrients since they are more slow-releasing and not as harmful as chemical ones 
• Always choose high-quality products 
• Flush your growing medium regularly with RO water 
• Learn about nutrient interactions

4. Wrong Pot Size 

If you are brave enough, you can grow cannabis in any container, even your old sock drawer, but since we’re not experimenting with science, it’s wise to choose the right kind of container, especially when it comes to its size. 

The pot you choose should be large enough for your cannabis plant’s roots. If the container is small, the roots may not get enough room to grow, which can lead to root binding, where the plant fails to grow larger. 

That doesn’t mean you choose a dump truck to grow cannabis, but you need to pick the right-sized container. If the container is too big, the nutrients can get lost in the soil without ever reaching the roots. 

So, whether you are using a plastic, ceramic, or fabric pot, you need to pick the right-sized one. The most common size is 2.5 gallons for indoor cannabis plants, so that’s a good starting point for most growers. Once your cannabis plant outgrows it, you can move to a bigger container. 

5. Other Root Issues 

Apart from the pH and the wrong container, your cannabis plant’s roots can run into other problems that can slow down its growth too. So, you must pay attention to the roots, especially if you are growing in soil since you can’t see the roots directly. 

Here are the common root problems you may encounter while growing cannabis.

• Overwatering 

Overwatering is a common problem that many new growers fall for. It’s easy to assume the more the merrier when it comes to watering cannabis plants, but that’s never the case. Giving your cannabis plant too much water can lead to all kinds of issues, including drooping leaves, stunted growth, yellowing leaves, and even mold in the growing medium. 

• Underwatering 

On the other hand, underwatering isn’t great either. When you do this, your plant does not get enough water and nutrients to sustain proper growth. Due to this, the plant may start wilting, appearing weak, showing signs of deficiency, and stunted growth. 

So, how do you deal with over- and under-watering? There’s a simple trick for this — use your fingers. When the top inch of the soil is dry, water your plant, and keep watering it until 25% of the water runs off the drain. 

• Lack of Oxygen in the Soil 

Did you know that your plant breathes via the roots, too? If the roots do not get enough aeration or oxygen, they may suffocate and fail to do their duty of absorbing the nutrients. When this happens, your cannabis plant may slow down in its growth. 

How do you fix this? By using a high-quality potting mix. If you’re already using soil but it has compacted over time, consider adding perlite or coco to the soil. These mediums offer excellent aeration and adding them to the soil can improve its aeration, too. 

6. Temperature and Humidity Issues

Cannabis, as a species, is strong and can withstand harsh conditions. There’s a reason why it can grow even in the Himalayas. But that doesn’t mean you let it grow in a harsh environment; it won’t grow as big as you’d expect it to. 

Most cannabis strains prefer a slightly warm and humid climate with minimal fluctuations. So, make sure your grow room’s environment is maintained well. 

For this, it is recommended that you get a thermo hygrometer that will allow you to measure the humidity and temperature of your grow room. If the temperature goes below 60°F (15.5°C) or over 85°F (29°C), you need to act quickly to bring it back to ideal levels. 

But that’s just a starting point; managing temperature and humidity for cannabis plants is more involved than that. Here are the temperature and humidity ranges you need to aim for during each of your plant’s growth stages:

• Seedling stage: 60% to 70% with temp between 70 to 80°F 
• Vegetative stage: 40% to 70% with temp between 70 to 95°F
• Flowering stage: 40% to 50% with temp between 65 to 85°F 
• Late flowering stage: 30% to 40%

Do note that when you decrease the humidity, do not do it instantly. Instead, reduce 5% per week and take it gradually. Otherwise, your plant may experience stress, which will further slow down its growth. 

7. Training Stress or Physical Damage 

Your cannabis plant is sturdy, but like your body, it can easily break under a lot of stress. Whether you used a heavy hand while training or the grow light fell on the plant, your plant can experience physical damage sometimes. 

When this happens, the plant has to redirect its nutrients to the damaged part to heal it, but this takes away the energy from other parts of the plant. This can lead to your cannabis plant not growing properly. 

So, how do you fix it? First, find the damaged part and try to fix it. For example, if your plant has a broken branch, wrap it with gardening tape, and let it heal. There’s not much you can do other than give your plant some time to recover on its own.

However, you can prevent this from happening again by regularly checking and fastening all the fixtures around your plant. When you are training, make sure you use the right methods and tools and do not be too hard on the plant. 

8. Pests 

Cannabis is no stranger to pests, but sometimes, these pests can create havoc in your garden if you don’t deal with them on time. Generally, these pests that attack cannabis plants come in three flavors:

• Those that suck nutrients from the plant
• Those that chew away the leaves and branches 
• Those who spread infectious diseases

All these types of pests have the potential to make your cannabis plant grow slower. The first kind will take vital nutrients from your plant, creating an energy deficit in the plant. The second one will chew away the leaves, which will hamper the plant’s photosynthesis process. Finally, the third kind can cause problems, ranging from fungal to viral infections, which can affect the plant in many ways. 

The most common pests your plant may encounter include whiteflies, caterpillars, spider mites, fungus gnats, slugs, snails, thrips, caterpillars, etc. 

So, how do you get rid of them? There are a few ways, such as the following.

• Use Neem Oil

The best way to deal with pests on cannabis plants is with neem oil, a natural pesticide that is completely safe for your cannabis plant. This works against most pests by coating them in oil and suffocating them. 

To use this to eliminate pests, you need to dilute it with water and spray it around the plant. Do note that neem oil is pungent, so do not use it on a flowering plant as it can leave a pungent flavor in the buds. 

Also, neem oil is usually safe for humans but it is a common allergen. So, make sure you are not allergic to neem oil. 

• Spinosad

On the other hand, you can also use spinosad. This is completely harmless to plants, children, and pests. Spinosad is made from the fermentation of a particular soil bacteria that kills pests by affecting their nervous systems. 

This pesticide is easy to use, too. All you need to do is mix it with water and spray it on the plant, like neem oil. And since the mixture is fairly diluted, you can be liberal with it, too. It works against crickets, grasshoppers, caterpillars, thrips, spider mites, and whiteflies. 

• Diatomaceous Earth 

You can also use diatomaceous earth, which is a powder that’s made from fossil dust. It is fluffy for us, but at a microscopic level, it is extremely sharp. It punctures insects to the touch, leaving them dehydrated. 

Do note that this is only good to be used as a sprinkler to keep the numbers in control. It won’t necessarily eliminate all the insects from your garden and won’t work if the soil is wet.

• Use Beneficial Insects 

One of the best ways of eliminating insects from your cannabis plant is by using beneficial insects that will do the hunting for you. The best beneficial insects include ladybugs, lacewings, predator mites, praying mantis, rove beetles, nematodes, green lacewings, etc. 

You can purchase them from your local horticultural store and leave them loose in your garden. Soon enough, they will start hunting down all the nasty pests that may be preying on your cannabis plant. 

Are You Overthinking This?

When growing cannabis, it is easy to fall into the trap of worrying too much, sometimes even unnecessarily. So, if you think your plant is growing slowly but there aren’t any noticeable signs of any problems, do you need to worry?

Sometimes, cannabis plants can grow slowly due to a few reasons. 

The first reason is genetics. Some strains are predisposed to grow slowly, especially in certain environments. So, make sure the cannabis strain that you are growing is not a slow-growing strain. Even if it is, there’s no need to worry. 

The genetic makeup determines how the plants grow and develop. Each strain's genetic composition influences its growth patterns, flowering behavior, and ability to withstand environmental challenges. Understanding how genetics impact cannabis cultivation helps in selecting the strains and cultivating practices to ensure a smooth growing operation.

In terms of growth rate, think of genetics as the roadmap where everything including the size, vigor, and speed with which the plants grow is predetermined. Some strains are genetically inclined to grow very quickly during the vegetative phase whereas others may perform well when they start flowering. These strains often exhibit traits that support growth, such as luxurious foliage, extensive branching, and efficient nutrient absorption.

Similarly, strains with genetic characteristics that tend to grow slowly will do the same. You will notice that the plants grow gradually rather than displaying quick bursts of vegetative growth which is common in many strains. Needless to say, they will also have extended flowering periods. 

Although slow growth may delay progress initially it can lead to denser buds with hefty amounts of resin over time. This slower pace of growth can be beneficial if you want to train the plants well and are in no hurry to harvest the plants. Moreover, even if the plant grows slowly due to its genetics, it will just take about 1-2 weeks extra. Thus, strains that grow slowly aren’t necessarily bad, but if you want faster harvests, make sure you read the description provided by the seed bank to understand the characteristics of the strain. 

In addition, you must consider several factors such as your local climate even if you’re growing indoors when choosing strains. Although it’s possible to manipulate the environmental conditions using air conditioners or air heaters to reduce or increase the temperature, it will help to choose strains that adapt well to your climate. This way, it becomes easier to grow strains without having to worry too much about the temperatures. 

The second reason is just nature doing its thing. Sometimes, everything can be perfect and the plant may still grow slowly. There’s nothing you can do about it. Let it grow at its own pace — it needs to do its thing. 

The third reason that your plant may be growing too slowly, to say the least, is if you are just being impatient. It’s exciting to wait for harvest, but sometimes, we may get too impatient with it. 

Avoid overthinking this. While we are not asking you to ignore your plant’s problems, it’s often wise to take a step back and look at the bigger picture — especially if you think your plant is growing too slowly but you can’t find a clear problem for it. 

How to Improve Growth

There are a few ways to help your cannabis plant grow faster. The techniques you use will significantly influence how your plants grow and as long as you choose seeds with good genetics, you can expect decent yields. But if you want more from your plant, you can use techniques like pruning to ensure the plants grow vigorously. Also, make sure you space your plants properly as it reduces the chances of pests and mold that occur due to high humidity. 

Let’s take a quick look at some strategies you can use to help your plants grow vigorously:

Pruning

Pruning involves removing sections of the cannabis plant like leaves, branches, or buds that have no potential to grow big. This method serves several purposes, but the biggest advantage is that it improves airflow and the plants’ exposure to light. By getting rid of excess foliage, you’re going to reduce humidity and improve ventilation in the canopy. In addition, since high humidity levels attract mold and powdery mildew, you’ll be able to prevent them as well. 

Once the excess leaves are removed, the leaves and branches in the lower parts of the plant also get more light, thereby helping them grow vigorously. Keep in mind that you can remove any part that’s preventing light exposure, including the buds. This way, the plant directs its energy towards the remaining buds that have the potential to grow big. However, do not remove too many buds as the purpose of this exercise is to increase the speed of plant growth to get more buds rather than getting rid of the buds themselves. Typically, you’ll want to remove popcorn buds that have no scope of getting any light. Other than that, just stick to leaves. 

If some sections of the plant are suffering from any diseases, you can remove them immediately to stop them from spreading to other parts or plants. Pests and diseases slow the plant down incredibly, so do everything possible to keep the grow room pest-free. 

Training

Cannabis typically grows like a Christmas tree with one main cola. The lower branches of the plant rarely get any light. However, if you can manipulate the plant to spread out and produce more colas, you will get more yields. Most training techniques are geared towards this concept. Through various techniques, you can alter the pattern of the plant so that it develops a uniform canopy and produces more buds. In short, you’re allowing all parts of the plant to get more light so the yields will be more too. 

• Topping

This method is pretty straightforward. Once the seedlings grow a few sets of leaves, remove the tip of the stem to encourage lateral branching and create multiple primary colas. It leads to a denser canopy but the plants will still get a lot of light if you combine this with other training techniques. Ultimately, the combination will produce more bud sites with many more buds. 

• Low-Stress Training (LST)

This is another training technique that improves the light distribution and encourages the plants to grow quickly. You will get better results if you pair this method with topping. Essentially, LST involves bending the branches of the plant to the sides of the container to promote horizontal growth and establish a flat uniform canopy. By spreading out the plant's branches, LST helps all parts of the plant get more light. Eventually, this will lead to more buds. 

Summary: Cannabis Plants Growing Slow: Top 8 Reasons And How To Fix Them

There you have it — some of the most common reasons that may be making your cannabis plant slow to grow. By addressing these factors, including lighting, nutrients, root health, pests, etc. you can be well-equipped to figure out and fix the problem and turn your plant into a thriving beauty. 

Lastly, remember that sometimes, Mother Nature has her own timeline. Due to the weather, strain, or genetics, your cannabis may be slow to grow naturally. So if you can’t find a clear cause but still think your plant is growing slowly, it’s worth taking a look at the strain’s characteristics.