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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.

Contents:

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.

Easy Start

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.

Common Cannabis Seedling Problems and How To Fix Them

Yellowing or deformed leaves, burnt tips, or even slow growth can be a sign that something is wrong, even though your seedling may be able to recover, it may have a toll on the final size and yields of your cannabis plants.

Problems with seedlings are common and can end up affecting them further into their life cycle so it’s vital you detect and fix them as soon as you can.

It’s definitely not hard to detect when something’s wrong, but if you’re a new grower, first you should know how a healthy seedling looks like.

1. Healthy cannabis seedlings

Cannabis seedlings start with two tiny round leaves named “cotyledons”, these leaves are already formed inside the seed and open up once the seed has been successfully germinated, after a couple of days, the first serrated leaves will appear, which indicates that your seedling is starting to grow.

As you seedling start developing, the first pair of true leaves will appear, the true leaves are the typical fingered leaves everybody knows, all of the leaves up to this point should be bright green, if not, it’s a sign that something is wrong, to help you diagnose what you may have, here are the most common cannabis problems.

2. Overwatering

Overwatering is one of the most common problems amongst growers, even though plants need water to grow, they also need oxygen to properly develop, and when overwatering, you may end up drowning your plants because of the lack of oxygen.

You may think What about plants grown in hydroponics? Well, in hydroponic setups, about ⅓ of the roots are kept out of the water, this way they can breathe at the same time that they absorb water so even though the roots are in the water, they still get the oxygen they need.

When your plants don’t get the amount of oxygen they need, the leaves will start getting droopy and if you don’t treat it for long, the leaves will start to get yellow.

If you are seeing any of these symptoms, it’s most likely the problem is being caused by any poor drainage or watering too often.

How to fix it

  • Don’t leave plants sitting in runoff water.
  • Get better containers such as Smart pots or Air pots.
  • Mix perlite into the soil to increase drainage and oxygenation.
  • Make drainage holes on the bottom of the container to allow water to drain.

3. Underwatering

Just like overwatering, underwatering is very common, especially among new growers who want to prevent overwatering and it can be quite confusing because the symptoms are basically the same as when overwatering.

It’s essential you make sure your plants have access to water at all times, the roots should be kept moist always because plants are constantly losing water through the process of transpiration and they need to be able to replenish the water in the leaves.

When there’s not enough water, cannabis plants stop performing their basic processes and dry out, eventually killing them so even though you should be careful when watering, you should definitely keep your plants watered.

How to fix it

  • Make sure the top part of the soil is always moist.
  • Mix soil with coco fiber or vermiculite to improve water retention.

4. Nutrient problems

Just like the symptoms of overwatering or underwatering, plants that suffer from a nutrient excess (overfeeding) will start to get yellow leaves or yellow spots, burnt tips, or show slower growth.

Problems related to nutrients are usually caused by giving nutrients too soon, giving too many nutrients at once or “hot” super soil or pre-amended soils.

Giving too many nutrients at a time can cause problems overnight, so we recommend watering your seedling with plain water and taking a look at the following table so you prevent any problem related to nutrients.

The ideal water for seedlings

Medium pH PPM
Soil 6.0-7.0 100-250
Coco, clay pellets, and hydro 5.5-6.2 300-400

Have in mind that these are estimates and you should check every day for problems and lower or increase these numbers if you see signs of deficiencies.

Giving nutrients too soon will overload the soil, and consequently, your seedling so remember that you shouldn’t feed for the first couple of weeks or at least give a low nutrient dose.

This can also happen with organic super soil, even though it’s organic, you need to wait until your super soil isn’t “hot” anymore, “hot” soil means that the mix is still undergoing through biological activities so you will have to wait around 30-45 days before you can use it, although this is not the case with all super soils so make sure you get more information on the product you’re using.

How to fix it

  • Make sure you adjust the nutrient dose according to the medium you’re growing in.
  • Wait at least 10 days before you start feeding your plants.
  • Read the instructions on the products you’re using.

5. Excessive heat

Excessive heat can also affect your plants, which will end up showing signs of heat stress, you will see the edges of the leaves turning up like tacos and they will start to get dry and crispy, and in more extreme cases, the leaves will start showing a yellowish-green color.

This can be caused by elevated temperatures, low humidity, or even the fans being too strong, but luckily, this can be easily spotted before your plants start showing the symptoms because you will see the soil is dry and sometimes it will start to crack.

How to fix it

  • Make sure the temperature and humidity are at the right levels.
  • Place your hand under the light fixture, if it’s too hot for you, it definitely is for your plants.
  • Ensure your fans are not too strong for the stage your plants are in.

6. Too much (or too little) light

Another common problem among new growers is not providing enough or providing too much light in the seedling stage, if your seedlings are not getting enough light, they will start stretching and the stem will get super long, which is a bad thing because they can easily snap and there’s no way to fix it.

Now, when your seedlings are getting too much light, or the lights are too close to them, the seedling will get dehydrated and the leaves will get burnt, showing symptoms like burned and wrinkled leaves.

How to fix it

  • Adjust the light fixture’s distance from the seedling every day, try to find the sweet spot.
  • Use CFLs instead of potent LEDs or HPS to avoid this kind of problem.

7. In conclusion

Seedlings are super fragile and sensitive so you should take good care of them, avoiding problems at this stage is vital because even though your baby plants may recover, the size and structure may be affected, which will end up affecting your harvest.

If you have tips you can share with fellow growers to help them take care of their baby plants, feel free to leave a comment in the comment section below!

Have you noticed your seedlings are not growing properly? Learn how to identify and fix those problems!