Why is my cannabis plant growing slowly or not at all? Find out the answer to this question and see what you can do to solve it. When your cannabis plants are growing slow or not at all, there is a reason for it. Find out about the top 10 reasons for slow cannabis growth. There are many factors that affect the growth of a cannabis seedling.
Slow Cannabis Plant Growth And What You Can Do About It
When your cannabis plants grow slowly or stop growing altogether, there is always a reason. It could be a problem with nutrients, an environmental factor, or something else entirely. Let’s explore the reasons your cannabis plants or seedlings may experience slow or stunted growth.
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“Why are my plants growing so slow?”. Sometimes, marijuana plant problems occur out of the blue. Your baby may not have shown any signs of an issue, but now you notice that development has halted and have no idea why. Here are some possible factors behind the slowed growth of your cannabis seedling or plant.
18 REASONS FOR SLOW OR STUNTED CANNABIS GROWTH
1. SEEDS ARE OLD OR LOW-QUALITY
Old seeds don’t just take longer to germinate (if they germinate at all); plants grown from aged seeds can also sometimes grow at a reduced pace. Likewise, good genetics are essential for healthy and vigorous growth from seed to harvest. A random bagseed will not perform nearly as well as quality seeds obtained from a reputable seedbank.
2. CLONE STRESS
Sometimes cuttings don’t root well, which hampers their growth. To prevent this from happening, apply a little bit of rooting hormone immediately after taking your cuttings.
Also, make sure your environment promotes root growth. The medium should be humid (but not too moist) with a pH level of about 6.0. Keep your cuttings at a temperature of around 22ºC. If they get too cold, they won’t root at all, and if it’s too hot, the roots will die.
3. ROOT HEALTH
When your plant’s roots can’t receive enough oxygen, metabolic functions slow down. In some cases, a lack of oxygen may stop their growth altogether. One common reason for this is overwatering or using substrates with poor drainage.
What to do about it? Create a light and airy growing medium with good drainage. You can improve poor-draining soil by adding some perlite.
The root zone for your cannabis plants should never get much hotter or colder than room temperature. Likewise, physical damage to the roots, mould, or bacteria can severely affect the growth of your plants. Always use non-transparent planters so light doesn’t reach the roots, as this is bad as well.
4. CANNABIS PLANTS STRETCH TOO MUCH
Stretching among seedlings can be particularly problematic. Multiple factors can induce this response, but the most likely culprit is a lack of light.
If your seedlings are spindly, increase light intensity or bring the lights closer. Prop them up with dowels as an aid during recovery. As a last resort, you can (carefully) replant them deeper into a new pot.
5. PLANTS ARE NOT GETTING ENOUGH LIGHT
Although requirements can vary from strain to strain, light is nonetheless a critical factor for the development of all cannabis plants. A lack of “good” light can absolutely lead to slowed growth. If you grow indoors and suspect that your plants aren’t getting enough light, try to decrease the distance between your lamps and the tops of plants. If you grow outdoors in pots, move your plants to a sunnier spot.
6. PLANTS ARE GETTING TOO MUCH LIGHT
Any type of stress on your cannabis plants, including many hours of exposure to direct sunlight without rest, can also halt or slow down growth. If you grow indoors and suspect light exposure to be the source of stress, decrease the intensity or move lamps further away from the canopy if possible. Know that seedlings are particularly sensitive to intense light! If you grow outdoors and you’re able to, move your plants into a spot where the light is diffused, such as around a shade tree.
7. INCORRECT LIGHT SPECTRUM
How fast and how vigorously plants grow are influenced by the spectrum of light they receive. Make sure you use the correct type of light according to each stage of growth. For healthy vegetative growth, you want a cooler light with more blue in its spectrum, a so-called “vegging light”. Lights with a warmer, more reddish spectrum are used for the flowering phase.
8. LIGHT STRESS: DARK CYCLE INTERRUPTION
Light is essential for all plants to grow. Any changes in light intensity or exposure will have an effect on growth. Flowering cannabis is especially susceptible to interruptions in the dark cycle. A light leak in your tent, stray light from a street lamp, and even a red light from a camera can disrupt flowering, and in a worst case scenario, can turn plants hermaphroditic. For that reason, it is very important to maintain complete darkness during the lights-off hours.
Exposing weed plants to irregular light hours can cause a hormone imbalance that confuses their internal clock. Your plants could flower prematurely, or they could revert back to the vegetative stage. If this happens, growth and yields will greatly suffer. For that reason, make sure to keep your light cycle consistent.
The above suggestions predominantly apply to photoperiod strains, as autoflowering cannabis flowers based on age rather than light exposure.
Overwatering is one of the most common mistakes made by new cannabis growers. It’s like suffocating your plants, and one of the main reasons behind slow growth, nutrient deficiencies, root rot, fungus, and many other problems. Don’t water too often and do not water on a fixed schedule. It is better water less frequently so that the soil can dry out between waterings. A good way to test whether you should water or not is to lift up the pot itself. If it feels quite light, it is time to water again.
10. NOT ENOUGH NUTRIENTS
Although not as common as overfeeding cannabis plants, an insufficient amount of nutrients for healthy growth can well be the reason for slow growth. Know that the nutrients found in most commercial potting mixes will only last for 3–4 weeks; afterwards, you will have to administer some more quality nutrients. Check the label of your nutrient products for the recommended dosage for healthy growth. Also know that your plant’s nutrient requirements are closely linked to the light intensity your plants are exposed to. Plants under intensive lights grow faster and will require more nutrients than plants under fluorescent lights, for example.
11. CALCIUM DEFICIENCY
Calcium is among those vital elements that your plant needs for healthy development. A lack of calcium can manifest in the following symptoms:
- Fresh growth is slow, twisted, and curled
- Young shoots are discoloured and turn purple or yellow
- Overall plant growth is slow and lacks vigour and vitality
- You can avoid a calcium deficiency by adding dolomitic lime to your soil or growing medium
Address a calcium deficiency immediately with commercial CalMag products that contain liquid calcium. You can add these products to your nutrient solution or administer them as a foliar spray.
Be aware that some growing media, like coco, increase the risk for a calcium deficiency. If you grow in coco, you should use special coco nutrients and/or regularly add CalMag to your nutrient regimen.
12. INCORRECT PH LEVEL
Incorrect pH level of your nutrient solution is among the most common reasons for cannabis growing problems, including slow growth. The reason for this is that cannabis thrives only in a relatively small window of suitable pH values. If the pH is off, the plants are unable to take in nutrients, even if they are present.
Make sure to dial in the correct pH level depending on your growing method. If you grow in soil, make sure the pH level is from 6.5 to 7.0. If you grow in hydro, an optimal pH level is 5.6 to 5.8. For soilless grows, such as coco, a pH level of 6.0 to 6.3 is optimal.
13. TEMPERATURES ARE TOO LOW OR TOO HIGH
Cannabis likes it warm to grow healthy, and does best at daytime temperatures between 25–30°C. Temperatures lower than that will slow down your plant’s metabolism, resulting in slower growth. But excessive temperatures are not optimal either. At very high temperatures, heat stress can also slow down or even halt plant growth altogether. If you grow indoors, adjust your temperature to a comfortable level. You can also provide some cooling with fans that blow a mild stream of air over your plants. This can also help prevent hot air pockets from forming inside your grow room.
14. PLANTING POTS ARE TOO BIG
Cannabis growers often start their seedlings in small cups. Later on, when the plants have reached an adequate size, they will “pot-up” to larger containers.
If you start your cannabis plants in containers that are too big, there is a high risk that you’ll overwater them. The issue is that seedlings cannot absorb all the moisture that is held in a large container, unlike mature cannabis, which can “drink” much more. Furthermore, a large pot will also take much longer to dry out.
To avoid the problems that come with too much soil and moisture, start seedlings in smaller containers until they’re growing vigorously. Once they have a set of 5–6 real leaves (not counting the cotyledons), then transfer them to a larger container, at least twice the current size.
If your seedling is already in a big container and you don’t want to or can’t move it into a smaller cup, water only a small area around the seedling.
• What Is The Right Size Pot For Your Cannabis Plant?
Use this rough guide to determine what size pot you should use for your cannabis plant:
- Plant height 30cm: 7.5–11l container
- Plant height 60cm: 11–19l container
- Plant height 90cm: 18–26l container
- Plant height 120cm: 22–37l container
- Plant height 150cm: 30–37l+ container
15. STRESS CAUSED BY PESTS / DISEASES
Insects, pests, and disease can cause damage and compromise a plant’s immune system. In a best case scenario, your plant may survive, but you will have poor yields. In the worst case, your plants could die.
Insects may feed on the leaves, affecting a plant’s ability to retain water and transpire. Other pests may damage the roots or cause additional problems. Any time your plant is sick or infested with insects, it will spend most of its energy defending itself and recovering from damage, which will slow down growth.
If your plants are infested, you’ll want to treat them immediately with appropriate measures. Even better, you can use preventative methods (e.g. neem oil, slug barriers, etc.) to minimise the risk for pest infestations. During all stages of growth, ensure that you regularly check for symptoms of pest infestations, including under the leaves.
16. STRESS CAUSED BY TISSUE DAMAGE
Physical damage, such as broken branches, can significantly slow your plant’s growth. Any damage will make the plant redirect valuable resources to repair wounds—resources that could be better spent on growing or flower production.
If you’re growing outdoors, situate your plants in an area sheltered from strong winds and heavy rains, and use chicken wire and stakes to maintain support.
Seedlings and young cannabis plants are especially vulnerable. Allow your seedlings to mature indoors for some weeks before setting them outside.
17. STRESS FROM CANNABIS TRAINING TECHNIQUES
Tissue damage from high-stress plant training techniques always causes some delay in plant development. But when you’re pruning excessively or too frequently, your plant may ultimately spend more energy repairing itself than growing.
If you plan on pruning, don’t overdo it. Be aware that each pruning can delay the development of your plant for days, if not weeks.
If you’re using other plant training techniques such as topping, make sure you start as early as possible. If you’re growing autoflowers, don’t use any plant training techniques that involve tissue damage, such as pruning and cutting.
18. AGE STRESS
Older cannabis plants have different nutritional requirements than young plants. Their tissues become hard and woody, they’re less vigorous, and they’re unable to take in as many nutrients.
Because of this, you’ll want to adjust your feeding regimen accordingly. Otherwise you risk overfeeding, which in turn results in stunted growth, deficiencies, and disease. Keep this in mind if you’re keeping mother plants around for a long time.
Top 10 Reasons For Slow Cannabis Growth
There can be many reasons why your cannabis plant is growing slow or has stopped growing altogether. It could be a factor in your growing environment such as temperature being off, a problem with nutrients, or something else. Let’s look at the top 10 reasons behind slow and stunted cannabis growth.
When you are growing cannabis, you may sometimes think that you have taken care of everything. Then, seemingly out of the blue, you notice that your plant has stopped growing or is only growing slowly. This can happen during all stages of your cannabis plant’s growth—early in the seedling stage or later in the vegetative growing phase. Why won’t your seedling grow? What could be the reason for your cannabis plant developing slower than it should? Here are some of the most common reasons for slow and stunted growth.
TOP REASONS FOR SLOW AND STUNTED CANNABIS GROWTH
Many cannabis growers, especially those new to cultivation, tend to overwater their plants. Overwatering is indeed one of the most common (and lethal) mistakes when it comes to growing weed, and can cause many growing problems as a result. Slow and stunted growth of your plant can be due to nutrient deficiencies, root rot, or infestation, all of which can be catalysed by excess water in the substrate. If you want to water your plant right, don’t do so on a schedule—just when your plant needs it. It is always better to water less often so that the soil can dry out. A good test of whether you should water your plants is to lift the pot. If the pot is heavy and damp, it’s not time; if the pot is light and dry, you’ll know it’s time to water.
2. NOT ENOUGH NUTRIENTS
Some cannabis growers have a tendency to overfeed their plants, but not giving plants enough nutrients is another culprit of slow growth. If you’re growing with a pre-fertilised potting mix, know that the nutrients in these will normally only last some weeks to a month. After that time, you need to administer your cannabis with phase-specific nutrients to support healthy development, and eventually, robust flowering. However, know that nutrient requirements for your plant can vary. This will depend on the strain that you’re growing, as well as other factors such as temperature and how much light your plant is getting. If you’re growing under intensive grow lights, your plant will need more nutrients than if it were growing under less light.
3. SEEDS ARE LOW IN QUALITY OR OLD
Low-quality or old cannabis seeds are a common reason for all sorts of growing problems. If you use low-quality seeds, your plant may grow slow and stunted, or your seed may not even germinate at all. For best results, choose only quality seeds like those you can get at Zambeza and other reputable seed banks. With Zambeza Seeds, you will receive the best genetics so your cannabis plant will have a great start to its life, and a much better chance of healthy growth throughout all stages.
4. YOUR PLANT IS NOT GETTING ENOUGH LIGHT
Cannabis needs a lot of light, especially in the flowering phase. But your plants will also need sufficient light to support their vegetative growth. Although light requirements may vary between strains, all plants need a baseline amount of light exposure to prosper. If you grow indoors and feel that your plants are not getting enough light, you should be able to simply lower your lights, decreasing the distance between the lamp and the canopy. If you’re growing outdoors, make sure you plant in a spot with a lot of direct sun, or move your pots around throughout the day to maximise sun exposure.
5. YOUR PLANT IS GETTING TOO MUCH LIGHT
Again, cannabis plants love and require a lot of light; but too much is not a good thing either. Constant direct exposure to intensive sunlight or high-intensity indoor grow lights can stress your plants, which can lead to slow growth and other problems. If you think that too much light is behind the issue and you are growing indoors, move your plants further away from your lights to decrease the intensity. If you’re growing outdoors in pots, move your plants to a location with diffused or partial sunlight if possible.
6. WRONG TYPE OF LIGHT
In addition to the amount of light, the spectrum of light plays an equally important role. Some types of grow lights, those with a warmer, more reddish light spectrum, are more suited for flowering, while other lights can emit a colder, blueish light that is better for the vegetative phase. Make sure that you use a light in the right spectrum, otherwise your plant may grow slower than normal. Many common grow lights today are suitable for both your plant’s vegetative and flowering phases. However, if you are not sure, make sure you read the description for the light or ask the vendor before you purchase.
7. CALCIUM DEFICIENCY
Cannabis requires many vital elements for healthy growth, and calcium is one of them. If your plant is experiencing a calcium deficiency, it will mostly affect new growth on top of your plant. You may observe symptoms such as slow or twisted new growth, or the leaves turning purple or yellow. In time, your whole plant will take on a sickly appearance.
Although most cannabis nutrients should contain adequate amounts of calcium for healthy growth, a deficiency can still occur. Some growing media such as coco increase the risk for a calcium deficiency. This is also why coco growers normally use special coco nutrients or add Cal-Mag products to their nutrient regimen. You can also add dolomitic lime to your soil to avoid a calcium deficiency.
8. PH PROBLEMS
Along with overwatering or overfeeding, problems with the pH value of the water or nutrient solution are a common reason for slowed growth. Cannabis is rather picky when it comes to correct pH value, and if your plant is not within a healthy pH window, it cannot take up nutrients—even if they are present.
If you grow your cannabis plant in soil, ensure that your water or nutrient solution has a pH value of 6.5–7.0. For hydro, the optimal pH for cannabis is 5.6–5.8. If you grow soilless, including in coco, make sure the pH value for your water sits at 6.0–6.3.
9. YOUR POTS ARE TOO BIG
Have you ever wondered why you should start your plant in a small pot and only later repot into a bigger container? The answer is that a tiny seedling cannot absorb all the moisture present in a large pot, which can lead to all sorts of troubles. Mature plants with a large root system won’t have this problem as they can drink much more. One other issue with large pots is that they will take much longer to dry out. And just as with overwatering, the large pot and the stagnant moisture can incite slowed growth and a host of other problems.
Always start your seed in a small container such as a cup or jiffy pot, then transfer it into a larger pot once your plant has a set of 5–6 leaves. If you have already planted your seed in a large pot, make sure that you water only in a small area around the seedling.
THE OPTIMAL POT SIZE FOR CANNABIS PLANTS
Plant height 30cm: 7.5–11l container
Plant height 60cm: 11–19l container
Plant height 90cm: 18–26l container
Plant height 120cm: 22–37l container
Plant height 150cm: 30–37l+ container
10. TEMPERATURES TOO LOW OR TOO HIGH
Cannabis, like many other plants, grows best at moderately warm temperatures. The optimal temperature range for growing weed is between 25 and 30°C, although nighttime temperatures should be a few degrees lower. If it is too cold, this will slow down your plant’s growth. Likewise, you want to avoid exposing your plants to excessive heat. Temperatures that are too high can also lead to slow growth or halt plant development altogether. If you are growing indoors, make sure that the temperatures are at a comfortable level for your plants and that your grow room is well-ventilated. Sometimes a simple fan can be all that’s needed to get grow room temperatures under control.
No reason to panic if your cannabis plant is growing slow! With our guide, you should be able to identify and address the most common reasons for slow and stunted growth.
I have a seedling started. It’s fruitcake and I started it in soil. My question is it’s a little droopy and I feel like I’m doing everything right with the amount of water and the light it’s got. It’s kind of growing slow. I think it’s in the third week and it’s only barely got the 3rd set of leaves coming out. I also read something about fruitcake and that all fruitcake strains are autoflower is that true? Thanks, Steven R.
There are many factors that affect the growth of a cannabis seedling. In general, seedlings need a consistently warm temperature (70-78°F), adequate lighting (kept at a proper distance), a photoperiod of 18 hours on/6 hours off, air movement, and an appropriately sized container with a well-aerated medium. Assuming your garden temperature falls within the desired range (70-78°F) and you are giving your plants the rest they need with an 18 hours on/6 hours off photoperiod, your problem may lie in your artificial lighting, air movement, or soil mix.
One way to test if the artificial light source is the proper distance from the plants is to place your hand under the light source, just above the tops of the seedlings, then wait 30 seconds. If your hand feels hot, it is likely too hot for sensitive seedlings and the light source should be moved farther away. On the other hand, if the light source is not close enough, the seedlings could get “stretchy.” A full-spectrum light source, or “white light” is ideal for early seedling development.
Proper air movement is essential for building a seedling’s structural integrity. High humidity environments, like that created with a humidity dome, are great for the first week or so, but a periodic removal of the dome to replenish the fresh air is advised. After the seedlings start to develop their first set of true leaves, they should be acclimated to an environment with adequate air movement. This can be easily accomplished by using an oscillating fan.
Lastly, a well-aerated soil mix in an appropriately sized planting container is crucial for healthy root development. Seedling specific soil mixes are generally a good choice as they are well-aerated and contain a ratio of nutrients specific for that stage of growth. Dense, compacted, or oversaturated soils will stunt the seedling’s growth.
As for your question about Fruitcake strains being autoflower, there are multiple seed companies that sell strains under various names. Reputable seed companies will have lineage descriptions for their hybrid strains. Autoflowering varieties will contain cannabis ruderalis in its lineage. Breeders have hybridized indica and sativa varieties with ruderalis to create high THC and CBD strains that autoflower or create flowers due to the age of the plant, not necessarily from the period of darkness, like photoperiod strains. I hope this answers your questions.