How to Prevent and Fix Stretching in Cannabis Seedlings
Long, stretchy stems are one of the most common problems growers face during the seedling stage. Luckily, there are a few simple ways to prevent and fix stretching in cannabis seedlings.
Fix stretching in cannabis seedlings, and prevent it from happening again.
Just like baby humans, cannabis seedlings are super fragile and need plenty of tender loving care to flourish. Unfortunately, many growers run into the same issue during the early stages of their cannabis plants’ lives; their seedlings grow long, stretchy, and weak stems. This, in turn, can lead to a host of issues that put your crop at risk of delivering subpar results.
Below, you’ll learn how to prevent and fix stretching in cannabis seedlings.
Understanding the Seedling Phase
Seeds are like little genetic time-capsule bombs. What this means is that they only have one job, and only get one chance to pull it off. They are pre-programmed to survive. A seed self-contains absolutely everything a future plant needs to get started. Once activated with moisture and darkness, it will trigger germination, and once that gets going, there is no turning back.
A seedling does not need any food for the first good few days of its life. From its genetics, it is already backpacking all the essential nutrients needed to embrace the miracle of life. Seedlings have a little reserve to help establish themselves in their growing environment.
In optimal conditions, the seed shell, or husk, will crack open and a taproot will pop out, immediately digging further down in search of a water lifeline. Soon, you will see a sprout rise from the under the soil, spread out its first baby leaves (cotyledons), and then you will start noticing the first set of true leaves. Leaves have an equally important job as the taproot, but they are in search of another food source – light. Quite literally, a plant uses light to digest what it brings up from the soil.
The Perfect Light Conditions for Cannabis Seedlings
To grow healthy seedlings, it’s important to give them the right amount and type of light as soon as they break out of their shells. Cannabis seedlings like to receive around 16 hours of light per day at an intensity of 375 lumens and 4000 lux.
To meet these requirements, we recommend using one 12W CFL bulb per 1–2 seedlings. Keep the bulb 5–7.5cm (2–3in) from the top of the seedlings and monitor their growth carefully, making sure the plants don’t make contact with the bulbs.
Growing your seedlings under lights with a high percentage of red light may cause them to stretch. Blue light, on the other hand, helps to keep internodal spacing to a minimum and encourages plants to grow nice and stocky from the get-go.
What Causes Abnormal Stretching?
Abnormal stretching in the seedling phase is a sign of stress. By far, the most common situation that causes seedlings to stretch and topple over is light deprivation.
In the same way taproots dig for water and nutrients, the top part of the plant will stretch vigorously if it’s not receiving enough light. It’s a survival mechanism in which a plant uses up all its stored energy to rise above competing flora. In the case of indoor growing, there is no competition, but the seedling will perceive it this way. For instance, leaving the pot under a windowsill in the shade will likely trigger this behaviour. Things can get even more dramatic under artificial light.
This may seem a bit confusing for new indoor growers, as they may think they are providing more than enough light to their plants. But consider the following: Positioning a 200W metal halide (MH) bulb relatively far from the pot will be less effective than a 20W CFL bulb placed a few inches from the leaf surface. Even though CFLs are much weaker than MH, light intensity drops significantly the further away plants are from the source.
Moreover, seedlings have very small, and few, leaves. The total surface area available to absorb light is very small. So, in essence, that 200W bulb will be radiating over a very large area, but the seedling can only use a minute fraction of it. The CFL positioned right over the plant, on the other hand, will be able to give most of its 20W directly.
Other Potential Causes of Stretchy Cannabis Seedlings
Besides light deprivation, there are a handful of other factors that could be causing your cannabis seedlings to stretch. One common cause of leggy seedlings is poor nutrient content in the soil.
More precisely, cannabis seedlings benefit from nitrate-derived nitrogen. Unlike ammoniacal nitrogen, nitrate-nitrogen is a lot easier for plants to absorb and fuels shorter, bushier vegetative growth. If your seedlings are stretching despite ideal light conditions, we highly recommend checking the ammoniacal nitrogen content in your soil and fertiliser.
Another cause of leggy seedlings is heat.
While cannabis seedlings like warm, humid conditions, too much heat can cause a plant’s leaves to grow slower than its stem, resulting in tall and stretchy growth. To promote healthy seedling growth, we recommend keeping the temperatures in your grow room or dome at 19–20°C during the day and roughly 13°C at night.
Finally, cannabis seedlings can also stretch if they’re receiving too much or not enough light per day.
While some growers opt to keep their seedlings under 24 hours of light per day, we recommend sticking to 16 hours. Seedlings are fragile, and giving them too much light can cause stress and stretching. Remember, those dark hours are just as important for your young plants to develop healthy roots and respire.
How to Keep Cannabis Seedlings From Stretching and Falling Over
Stretchy cannabis seedlings can be a pain to handle and transplant. Their stems can be very fragile, and once they start vegging, their foliage can be off-centre due to the weird stretch they underwent as seedlings.
For best results, we recommend replanting your stretching seedlings deeper into their soil, correcting your lighting, and checking the nitrogen levels in your soil and/or fertilisers (as mentioned above). Once you’re confident you’ve created the right environment for your seedlings, pop them back under their lights and monitor their growth. Over time, the buried overgrown stem should sprout roots.
If possible, you may want to consider growing your seedlings outdoors under direct sunlight. There is simply no substitute for Mother Nature, and seedlings in direct sunlight will grow healthy, strong stems with short internodes. Once your plants have developed 2–3 mature leaves, feel free to move them indoors, making sure to keep their lights at the right height to prevent any further stretching.
If you have to grow your seedlings indoors, use the setup described above to ensure they get enough direct light at the right intensity.
Soon, you should notice your seedlings developing healthier growth. Short internodes and compact, green foliage are all signs that your seedlings are growing perfectly.
Note: Some growers try tying their stretchy seedlings to a stake. We do not recommend this method, as it doesn’t do anything to combat the weak, overgrown stem or the difficulty it’ll present further along in the grow.
Thinning Your Cannabis Seedling Crop to Prevent Stretching
Thinning is a common agricultural technique that’s often forgotten among cannabis growers. As the name suggests, thinning is all about reducing competition among your plants by “thinning” out the population.
Cannabis plants grow very quickly and will naturally compete with one another for space, light, and nutrients. So, while you may have been taught to think that more plants will naturally translate into bigger, better harvests—that might not be the case. In fact, many experienced growers opt to cull their weakest seedlings and only grow those plants that show the healthiest growth. This way, they focus their efforts on the plants most likely to produce the best flowers.
Thinning also helps growers maintain an even canopy across their grow room, which makes better use of a limited amount of light and space. Finally, thinning can help you avoid pests and other plagues, as you’ll be less likely to end up with a crowded grow space.
To thin your plants, simply keep a close eye on your seedlings throughout the first 1–2 weeks of their life, and only keep those specimens that show the healthiest, fastest growth.
Are your cannabis seedlings growing long, stretchy stems? Here's how to prevent and fix stretching during the cannabis seedling stage.
How to care for your cannabis seedling
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- What happens during the seedling stage?
- Choose the right container
- Be mindful of how much you water your cannabis seedlings
- Know the signs of nutrient deficiencies
- Choose the right lighting
- Keep your environment at the right temperature and humidity
- Get out there and grow your seedling into a full-grown marijuana plant
When you’re growing cannabis, you want to keep your plants strong and healthy through every stage of the growing process — and that includes the seedling stage.
The seedling stage can be an especially vulnerable time in the growing process. The cannabis seedling is in need of a lot of TLC to grow into a healthy cannabis plant.
In the seedling stage the cannabis seedling is in need of a lot of TLC to grow into a healthy cannabis plant. Photo by: Gina Coleman/Weedmaps
But what does that TLC look like? What steps do you need to take to support your cannabis seedlings through the seedling stage and as they grow into mature marijuana plants?
Let’s take a deep dive into how to care for your baby marijuana plant so you know exactly how to take care of your growing seedling and make sure it grows into a healthy, mature cannabis plant.
What happens during the seedling stage?
Before we jump into how to care for your cannabis seedling, let’s quickly cover what happens during this grow stage.
The growing process has four key stages: the seed germination stage, the seedling stage, the vegetative stage, and the flowering stage. Once the cannabis seeds germinate and are placed into their growing medium (like a potting mix), they start to root into the soil as the stem grows upward, sprouting two cotyledon leaves, which help the plant absorb light and continue to grow.
As the plant grows, it starts to produce more fan leaves — and those leaves continue to develop the ridged edges that you’ll immediately recognize as the marijuana plant. As more leaves grow, more ridged edges develop until finally, the plant is fully grown with each leaf reaching its maximum number of edges (which can be anywhere from 5 ridges per leaf to upwards of 10).
This stage — moving from germinated cannabis seeds to cannabis plants with the maximum number of ridged edges per leaf — is the seedling stage.
The seedling stage is an incredibly important part of the growing process; because the cannabis plant is still young and fragile, proper care is essential if you want to lay the foundation for a healthy mature plant.
But what does that care look like? What are the key things to know when it comes to how to take care of marijuana seedlings?
Choose the right container
Your cannabis seedling needs space to grow. But too much space and too little space can both create problems for your plant.
If you try to grow your seedling in a container that’s too large, the root system won’t be able to absorb all the water in the soil. If you start growing your seedling in a container that’s too small, the roots won’t have space to extend and will start to wrap around themselves, which will also impact their ability to absorb water.
Choosing the right pot is an essential part of caring for your growing plant. You need a pot that’s going to give the root system space to grow, but not so much space that the roots won’t be able to absorb all the water in the soil. You should also make sure the pot has drainage holes to get rid of any excess water that could overwhelm the plant.
Choosing the right pot is an essential part of caring for your growing plant. Photo by: Gina Coleman/Weedmaps
Be mindful of how much you water your cannabis seedlings
When it comes to watering your seedlings, you want to give them the water they need to thrive. But too much water can actually have a negative impact on the growth process, so it’s important to be mindful of how much you water your seedlings.
The root system of a seedling isn’t elaborate; the roots are small and don’t need much water to grow. Misting the plants with water once or twice a day should be plenty to give them the hydration they need to grow.
If you’re not sure how much water is too much water, keep in mind that you want the growing medium (AKA the soil) to be damp and moist — not soaked and oversaturated.
Know the signs of nutrient deficiencies
A nutrient deficiency can cause serious issues for your growing plant, so part of proper care is knowing how to spot the signs of a nutrient deficiency.
Nutrient deficiencies can come from a variety of places. “Hot” potting mixes that contain too many nutrients could cause nutrient toxicity. On the other end of the spectrum, under-watering can cause a deficiency in the key nutrients your plant needs to grow.
Some red flags that signal your seedling may have a deficiency in nutrients (or nutrient toxicity) include:
- Dark coloring (cannabis seedlings should be a vibrant shade of green)
- A burned appearance on the tip of the leaves
- A curling on the tip of the leaves
- Yellowing leaves
If you notice any of these issues with your plant, it could be the result of too many or too few nutrients. You’ll need to adjust your growing strategy to support your plant’s health.
Choose the right lighting
Like any plant, seedlings need light in order to grow and thrive. But not all light is created equal. If you want your seedling to grow into a healthy cannabis plant, you need to expose it to the right type of light.
If you’re growing your seedlings outdoors, they’ll need to be exposed to as much sunlight as possible. Keep them in the sun from sunrise to sunset; the more sunlight exposure they get, the better.
If you’re growing your seedlings outdoors, they’ll need to be exposed to as much sunlight as possible. Photo by: Gina Coleman/Weedmaps
But growing your seedlings outdoors can be tricky. Because you can’t control sunlight, there’s no way to ensure your cannabis seedlings are getting the light they need to grow properly. A cloudy day can prevent your seedlings from getting enough light and throw off your entire growth process.
Growing your seedlings indoors with artificial light gives you more control over the process, making it easier to ensure your plants are getting enough light each day. If you’re growing with artificial lights (compact fluorescent lights that emit cooler, blue spectrum light are especially effective), aim to give your plants 18 hours on and six hours off each day.
Keep your environment at the right temperature and humidity
Environmental conditions are essential to growing healthy cannabis seedlings, and some of the most important conditions to control are temperature and humidity.
The temperature in your grow environment shouldn’t exceed 80 degrees Fahrenheit, otherwise the seedlings may grow too tall. (You should also plan on lowering the temperature at night to about 70 degrees Fahrenheit.)
You should also aim to keep humidity in the grow environment at a higher level, typically around 70 percent. That way, the plants can absorb moisture from the environment to develop stronger roots without getting weighed down by over-watering.
Get out there and grow your seedling into a full-grown marijuana plant
Watching your cannabis seeds transform into seedlings is an exciting part of the growth process. And now that you know how to care for your cannabis seedling, you should have everything you need to transform your seedling into a mature, healthy, and flowering cannabis plant.
How to care for your cannabis seedling Copy article link to clipboard. Link copied to clipboard. Contents What happens during the seedling stage? Choose the right container