Common Cannabis Seedling Problems and How To Fix Them

Have you noticed your seedlings are not growing properly? Learn how to identify and fix them!
20 October 2020
11 min read
Common Cannabis Seedling Problems and How To Fix Them

Contents:

 

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.

 

Common cannabis seedling problems: healthy seedlings

Healthy cannabis seedling.
 

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 cannabis 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.

 

Common cannabis seedling problems: overwatering

Overwatered cannabis symptoms.
 

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.

 

Common cannabis seedling problems: underwatering

Underwatered cannabis symptoms.
 

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

MediumpHPPM
Soil6.0-7.0100-250
Coco, clay pellets, and hydro5.5-6.2300-400

 

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.

 

Common cannabis seedling problems: excessive heat

Cannabis heat stress symptoms.
 

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.

 

Common cannabis seedling problems: light

Too much or too little light symptoms on cannabis seedlings.
 

 

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 cannabis growing 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!

 

External References:

  1. Seedlings. - Jenkins, Elwyn. (2020).
  2. Effect of seedling grades on seedling vigour of Azadirachta indica. - Mani, Gangadharan & A.Bharathi,. (2020).

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20 October 2020
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