Why Are Your Weed Plants Growing Slow?

Why are my weed plants growing so slow?” is a question and an issue no grower wants to face, but one that they’ll eventually run into.

Slow plant growth can be caused by a number of things, both in the plant and how it’s grown. Let’s discuss the top reasons for slow plant growth in your garden and how spotting early signs of slow growth can save your cannabis plants.

Help, My Weed Plants Are Growing Slow Out Doors!

Although cannabis can grow in just about any place, like a closet or the outdoors, the process from seed to harvest is tricky if you’re looking to grow quality buds.

Especially if we’re talking about growing photoperiod cannabis outdoors where it’s detrimental for you and your cannabis if they take their sweet time growing.

If you’re new to growing, photoperiod cannabis are strains that only flower once they’re exposed to a 12 hour light and 12 hour dark cycle. Because they rely on sunlight, outdoor growers have it hard when it comes to growing photoperiod cannabis.

Time is of the essence because you’re at the mercy of the season. You need to raise your cannabis plant until it reaches at least 4 feet tall. You also need to keep your plants healthy.

If you fail to meet the needs of your plants before mid-autumn, you’ll end up with fewer buds. Most growers counteract this by tricking their plants into staying into their vegetative phase with artificial light until they reach the right size for flowering. But the cost of that alone isn’t cheap.

So it’s a lose-lose situation. Slow plant growth affects indoor growers, too since It means that they’ll need to keep the lights on longer which adds onto the electrical cost. And if you’re trying to grow cannabis plants discreetly, a higher electricity bill means you’re more likely to be discovered.

How can you solve this problem? Be proactive. Look for early warning signs of slow plant growth by checking the condition of your cannabis’ leaves. Typically the early signs of slow growth appear when the leaves are:

Download my free marijuana grow guide and start growing high quality marijuana

Top Reasons for Slow Cannabis Growth & How to Deal with Them

Poor Genetics

The obvious cause for slow plant growth is using seeds with poor genetics.

This happens when you use old seeds that were lying around or random seeds you got from a fellow enthusiast. Seeds with bad genes will take a while to germinate and longer to grow. They may not even germinate at all.

Stop trying to figure out the answer to “what are the reasons why my weed plants are growing slow?” Make it a bit easier on yourself. Choose high-quality seeds with guaranteed germination. You can buy the best cannabis genetics in my seed store. 

But what if you’re working with clones that you got from a parent with good genetics? Your problem may be rooting issues in your cuttings that have hindered their growth.

To fix this, dip the bottom of your cuttings in apple cider vinegar before putting them in your rooting medium. Apple cider vinegar, as well as vinegar and water, act as a natural rooting hormone that helps promote root development in your clones. You can also use chemical solutions if you have them on hand.

nutritional deficiency in marijuana plants
Nutrient Deficiency in Marijuana

Nutrient Deficiencies

Nutrient deficiency is often mistaken for nutrient burn due to the similarities in their early signs. But nutrient deficiencies should be as much of a concern to growers as overfeeding their plants.

If improperly treated, a lack of nutrients will cause irreparable damage to your cannabis and result in slow growth.

One way to identify whether the problem is oversaturating your plants with nutrients or depriving them is to know how long the nutrients in the commercial potting mix you’re growing them in will last (typically, it’s 3-4 weeks).

The other thing to take into account is the stage of your cannabis. When your plants are in their vegetative phase, they require a lot of nitrogen.

Nitrogen is responsible for the plants’ growth and is a key element in the process of photosynthesis.

You’ll need a lot during the vegetative stage, but it’s important to switch out the type of fertilizer once your cannabis is in its flowering phase, where it doesn’t require as much nitrogen.

Learn more about cannabis nutrients in this cannabis feeding guide

Keep in mind, other factors can cause a nutrient deficiency in your plants,  such as light exposure and the type of growing medium you’re using.

Overwatering Marijuana Plants

Water is essential to your cannabis’ ability to transpire. But too much of it can drown or stunt your plants. Transpiration is a process of water movement throughout your plant that sends needed nutrients that help with its growth.

It’s typically helpful, but did you know that almost all of the water you give your cannabis (97-99.5% of it!) is lost through transpiration and guttation?

This fact explains why it’s easy to drown your plants by overwatering them accidentally, especially if you’re the type of person who uses fixed watering schedules. Why is this?

Shouldn’t it be less likely because you’re timing it? Not necessarily. There’s this thing called vapor pressure deficit (VPD), and essentially it affects the transpiration process in your cannabis.

If your cannabis can’t transpire effectively, your soil becomes waterlogged from the excess water your plant couldn’t absorb.

over watering marijuana plants
Overwatering Marijuana Plants

Your soil can also become waterlogged if it isn’t well-aerated or if your pot has poor drainage. If left as is, the roots of your cannabis will struggle with getting oxygen and cause it to stop growing.

Or worse, they develop root rot. The way to avoid this is to get a well-draining pot and add perlite to your soil.

Learn more on how to prevent overwatering in this cannabis watering guide.

Incorrect Lighting for Cannabis Plants

Proper lighting is key to healthy cannabis growth. If you have an indoor setup, ensuring proper light coverage for your cannabis garden should be one of your main concerns. Depending on how you situate your grow lights, your lights will affect the growth of your cannabis. 

If you place your grow lights too close, your cannabis is at risk of its leaves burning. And if you’re growing seedlings or clones, the intense light would hamper their growth.

If you place them too far or at an awkward angle, your plants will devote most of their development to stretching towards the light rather than growing. The result is a lanky cannabis plant with sparse branches that, on harvest, will produce low yields.

Outside of where you place your grow lights, the type you use can greatly affect plant growth. HIDs are ideal for cannabis.

They come in both Metal Halide (MH) and High-Pressure Sodium (HPS). You’d need to vary your lights based on your plant’s growing stage since cannabis responds to different shades of light. MH offers a cooler blue light that’s good for your plants’ vegetative phase, while HPS is ideal for flowering cannabis due to its warm, reddish light.

Learn about cannabis lighting options in this marijuana lighting guide

Marijuana Plant Temperature Problems

Temperature plays a vital role in your cannabis’ plant growth and health as it affects its ability to photosynthesize and respire. When temperature increases, the rate of photosynthesis and respiration also increases in your cannabis plants.

However, when the temperature becomes uncomfortably high for your plants, it would have the opposite effect on them.

Unfavorably low temperatures can also hinder plant growth in cannabis as it slows down their metabolic functions.

So how do you avoid high temperatures?

For outdoor growers, this isn’t much of a concern; however, it is a bit of a challenge for indoor growers, mainly because grow lights produce heat. Even the best lights can produce heat, and if not checked, it will cause the temperature in your grow room to fluctuate.

Although HIDs are ideal for cannabis growing, they produce a lot of heat which can be difficult to control.

What’s the ideal temperature for marijuana growing? Learn more in this cannabis temperature guide.

Temperature Guide For Marijuana
Temperature Guide For Marijuana

High-Stress Training

Although it’s in your best interest as a grower to maximize the yield of your cannabis plants, it’s important to know the amount of stress that’s good for them.

It may be called high-stress training, but there’s a point where too much stress can slow your cannabis’ plants growth or, worse, permanently damage them.

And it’s also important to take note that any technique that involves damaging the tissue of your plants, such as pruning, topping, and mainlining, can delay your cannabis’ development for days, if not weeks. This is because your plants are spending more energy on repairing than growing larger.

To avoid overstressing your plants, exercise proper pruning and apply the right amount of stress to your plants.

Remember, different types of strains respond differently to HST, such as autoflowering strains. Although not impossible, it’s extremely difficult to top and mainline autoflowers since they tend to enter their flowering phase in response to high stress.

And by that point, it’s impossible to salvage the plant.

Learn more about autoflowers in this guide on cannabis seed types.

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Seeds that grows faster

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Not Enough Darkness

Just as light and temperature play a vital role in the growth of your cannabis, their dark cycles are equally important. Although considered “rest time” for your cannabis, darkness doesn’t necessarily mean nothing is happening.

They may not be able to photosynthesize, but plants can still respire. It may not be as productive as photosynthesis, but it’s enough to keep them alive and gradually develop at night.

In particular, dark cycles are vital for flowering cannabis. If you interrupt them during this cycle by leaving your grow lights on throughout the night, it will cause the buds of your cannabis to stop growing.

And, as a worst-case scenario, your flowering cannabis might hermie and ruin the buds by pollinating them.

It’s easy to avoid this issue, mainly because it only concerns flowering cannabis.

It’s not much of a worry when your cannabis is still in its vegetative phase; during this stage,  it’s safe for you to bathe them in light for longer periods.

Marijuana Plants Growing Slow? It’s not over yet!

If you see signs that your cannabis is growing slowly, don’t lose hope because it’s not the end. When it comes to growing cannabis, many issues show up early enough to correct – if you know what symptoms you’re looking at.

I highly recommend reading our symptom checker to compare your plant’s issues and identify problems by looking at its leaves.

Here are some amazing seed deals. Buy 10 and get 10 seeds for free!

Frequently Asked Questions

What are some problems with slow growth?

For cannabis plants grown outdoors, slow growth generally means that they will miss the optimal sunlight exposure. This will leave you with smaller buds because your plants didn’t bloom during a period of strong sunlight. Slow growth can also result in small buds in autoflowers. This is because this strain of cannabis flowers regardless if it’s in the right conditions or not.

Can you fix stunted growth in weed plants?

Stunted growth in your cannabis plants will mean that you need more time for them to grow in their vegetation stage. This isn’t so hard for photoperiod cannabis, but with autoflowers, you may find it harder to trick them into not flowering. However, you can remedy this problem by applying fertilizers as a quick fix that works most of the time.

How big should a weed plant be at two weeks?

Generally, you should expect your weed plant to be 2-3 inches (5-7cm) tall with 3 nodes that include the cotyledons (which are the seed leaves). If your plant is not this size by two weeks, you may be experiencing slow growth.

Avatar for Robert Bergman

Mr Robert Bergman PhD


Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations ... See profile

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2 comments on “Why Are Your Weed Plants Growing Slow?”

  1. Hi Jeffrey,

    Thanks for your comment. I went and checked your order and you appear to have ordered photo-period seeds from us.
    So these will require a 12/12 light schedule to start flowering.
    I will make sure our customer support team reaches out to you about this as well.
    Kind regards,