Cannabis Seedling Help Handbook

Updated Mar 15, 2020

by Nebula Haze

Emergency Resources for Sick Seedlings!

Sometimes the hardest part of growing cannabis is getting started. If you’ve never gardened or planted a seed before, you may have to learn everything from scratch. And with expensive and hard-to-get marijuana seeds, there’s a lot of pressure to get things right!

At GWE, we have resources for almost every common growing problem, so make sure to always use the search bar on the side of the website if you have a specific problem.

Additionally, this tutorial will help you with some of the most common seedling problems, so you can get solutions quickly! Make it so that your first few weeks go without a hitch!

Example of a healthy and happy 10 day old cannabis seedling in a solo cup

 

My Seedling Problem is…

If your seedlings are sick and you’re still investigating the problem, move your grow light up and don’t attempt to train your plants or do anything new until they’re better! If you avoid stressing them out any further, they often recover much more quickly.

Germination Problems

Germination problems? We’ve got you covered!

 

Yellow Leaves

  • Why do seedlings turn yellow? – There are many reasons you might see a yellowing leaf on young plants, but this tutorial breaks down the most common.

This yellow seedling was overwatered. Seedlings don’t like “wet feet”. Too much water is the most common reason you’ll see yellow leaves on seedlings.

This seedling has stayed small with stunted leaves because it has been overwatered, with thick soil

 

Curling or Clawing Leaves

  • Clawing or curling leaves – Like yellow leaves, there are actually a few different triggers for clawing or curling, including watering practices and nutrient levels.

In this case, the clawed leaves are also from too much water. Small seedlings in big pots need careful watering until they’re drinking more.

Bad soil will sabotage you! Thick muddy soil prevents seedling roots from getting enough oxygen

This seedling started "damping off" (dying) due to terrible soil

 

Seedling is Wilting or Droopy

If you notice your plant is droopy all the time (even in the mornings right after lights turn on, when plants are at their perkiest), it usually means there’s something going on at the roots. The seedling might be getting too much or too little water at a time, possibly watering too often or infrequently, or its roots could be sick/damaged. The other major cause of drooping and wilting is high or low temperatures, and occasionally really high or low humidity.

This seedling was given too much water for many days. Notice the green algae growing on top of the soil.

This marijuana plant was overwatered for over a week, causing these odd symptoms in addition to persistent droopiness

Underwatered seedling – When there’s not enough water at the roots, leaves are dark green, possibly clawed or droopy, and growth is slow

Bone dry soils created problems for this underwatered seedlingIn hydroponics, when you see a droopy seedling it usually means there’s something bad happening at the roots

 

Burnt Leaf Tips

Seedling with a single burnt leaf due to slight underwatering. You can tell it’s not nutrient burn because it’s only affecting a single leaf (nutrient burn tends to affect leaves all over the plant).

Nutrient burn (tip burn)

 

Why Are Stems Purple or Red?

Purple stems are normal for some strains, though they also appear on plants that are cold, stressed or experiencing a nutrient deficiency. Sometimes bright light triggers purple stems, like a tan.

This seedling appears healthy. If you don’t see any other symptoms, you probably don’t need to worry about it. But keep a close eye. If a seedling with purple stems also grows slow or has markings on the leaves, it means something is wrong. Investigate!

A cannabis seedling growing its first few sets of leaves

 

Why is My Seedling So Tall?

Tall, “leggy” seedlings need more light. They’re doing their best to stretch towards the nearest light source! Quick aside: Avoid germinating multiple seedlings in the same pot. It can be difficult to separate them.

Cannabis seedlings will grow long and lanky if they're not getting enough light, even if that light has a lot of blue in it

 

Why Are Leaves Curling?

These wavy leaves are the result of too much heat, and possibly slight overwatering

The tips of this seedling's leaves are folded down due to heat

Another example of heat damage plus overwatering (the same triggers can be expressed in multiple ways)

More heat damage

A little heat will cause some problems like leaf tacoing and discoloration, like you can see with this heat-stressed marijuana seedling

 

Bugs or Pests

Learn more about fungus gnats

Fungus gnats looks like tiny flies buzzing around the soil, and are typically triggered by wet soil conditions

 

Something Else?

Re-vegging (pictured below) and other plant problems can be hard to diagnose. Use our free plant doctor tool to check your symptoms.

This cannabis was put outside too early in the year, causing it to re-vegetate with strainge twisted growth

Bonus Articles!

 

​What to Focus on During Your Seedling’s First Month

  • Perfect Environment – humidity, temperature, airflow, CO2/fresh air, reflective walls, etc
  • Enough Light – If your seedlings are growing tall it means that they want more light! Remember, in the flowering stage your yields will be directly related to how much light your buds are getting!
  • Not Too Much of Light Too much light can hurt your plants even in cool temperatures! Seedlings are more sensitive than adult plants, so be careful not to overload them with light too quickly! If you think your seedlings may be stressed from too high levels of light, move your grow light up a few inches and see if they improve.
  • Watering properly (one of the hardest parts for a lot of new growers!) – How to Water Plants Perfectly Every Time. I promise it gets easier!
  • Not Too Much Love – Seedlings need some breathing room! (i.e. avoid overwatering, touching/messing with plants too much, giving too high levels of nutrients or supplements, etc.). They want you to love them and watch out for them, but they also need to get work done 🙂
  • Start Thinking About Plant Sex – For several weeks after germination, a plant’s sex is hidden and has little effect on how your plants grow. However, if you are not familiar with the difference between male and female plants (only female plants make buds), now is the perfect time to read up!

 


 

 

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