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How to Help Yellow Cannabis Seedlings


by Nebula Haze

Having a problem with your cannabis seedlings? Here's a quock tutorial to help you identify the problem and get it solved right away so you can get back to growing marijuana!

What Causes Cannabis Seedlings to Turn Yellow (or Show Other Symptoms)?

  • Poor Watering Practices - When it comes to seedlings, the most common problem is overwatering. Leaves may turn yellow if roots stay wet for long periods of time ("wet feet") and may also show a wide variety of other symptoms, spots and nutrient deficiencies. Less commonly similar symptoms can be caused by underwatering but it's more rare because small plants don't drink much. Learn how to water your cannabis plants.
  • Bad Soil - If soil is thick and muddy, your seedlings will grow poorly. Good cannabis soil drains well and is rich and light.
  • Not Enough Light - Seedlings get long and stretchy with big spaces between sets of leaves, often with yellowing. What type of grow lights are good for cannabis plants?
  • Too Much Light - Parts of the plant closest to the light is turning yellow or brown. Learn about light burn
  • Too Hot or Dry - This can cause leaves to turn into tacos, crinkle up at the edges, and sometimes turn yellow if it gets too bad! Learn about heat stress and controlling temperatures!
  • Incorrect pH - If pH is too high or too low the plant may show nitrogen or other deficiencies. Learn about controlling pH to prevent nutrient deficiencies. As long as your plant is getting nutrients and doesn't appear droopy, 9/10 times the nutrient deficiency is actually being caused by the incorrect ph!
  • Not Enough Nutrients (rare) - If growing in soil, it's very unlikely your seedling will use up all the nutrients in the first few weeks. However, if growing in coco or hydro, it's important to give seedlings suitable nutrients from the beginning or they will immediately start turning yellow from the bottom up.

Examples of Unhealthy Cannabis Seedlings

Overwatering - Common cause of droopiness and yellow leaves

Overwatered marijuana plant - pot is too big

Overwatered cannabis seedling has turned almost completely yellow

Droopy seedling was overwatered in a too-big container, so the roots are having trouble getting the oxygen they need to grow

Another example of a deficiency that's actually caused by overwatering

Another example of a deficiency caused by overwatering

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

Chronic overwatering in thick soil led to the following yellow leaf symptoms. The main thing that alerts you to the fact that the yellowing is caused by overwatering is the fact that the seedling is droopy. It's very easy to overwater young plants when you have a small seedling in a big container. When that's the case, don't soak the whole growing medium. Water in just a circle around the plant until its leaves are up and growing fast. At that point you can start watering more thoroughly :)

Example of an overwatered young cannabis plant with yellow leaves in a too-big pot

The strange yellow and red growth in this picture has been caused by giving the plant too much water, too often. Overwatering can often causes what appears to be nutrient deficencies in young plnats! Older plants tend to just droop, but especially seedlings can have really odd reactions to root problems.

The strange yellow and red growth in this picture has been caused by giving the plant too much water, too often
 

Bad Soil - What Soil is Good for Cannabis?

Sick seedling - way too wet growing medium - extreme case of seedling overwatering

This soil is thick and thoroughly saturated with water. As a result the young seedling roots can't get any oxygen and it's stopped growing, with the first set of leaves starting to turn yellow. Overwatering will stunt young plants and keep them small!

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

This “soil” is more like mud. The plant roots are drowning from lack of oxygen, causing severe wilting. 

This cannabis seedling is sitting in a mud-like growing medium, causing symptoms of overwatering

 

Not Enough Light - Tall or "Stretchy" Seedlings

Tall seedlings are "stretching" because they're not getting enough light

Seedlings stay yellow if they never get any light

This stretchy cannabis seedling is yellow and tall because it has not been getting enough light

 

Too Much Light - parts of plants closest to the light are turning yellow

This cannabis seedling is being burned by too-close LED grow lights

 

Heat Stress - Causes leaves to fold into tacos and edges to turn up

A cannabis seedling suffering from heat stress - notice how the edges are curling upwards

These two seedsling are suffering partly from overwatering, and partly heat

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

These odd curling leaves symptoms are cause by root problems - partly from overwatering and partly from heat

After being subjected to overwatering plus a heat wave, the leaves of the following seedling started cuppping upwards and turned lime green. The stems and veins of the leaves were turning red. You can see the soil is still dark and wet because the plant stopped drinking after developing root problems.

This cannabis plant's leaves turned lime green when it developed root problems
 

Not Enough Nutrients

Not enough overall levels of nutrients usually only happens to cannabis seedlings in coco or hydro where the grower didn't provide any extra nutrients. It's rare for a young seedling in soil to be able to use up all the nutrients in soil in the first few weeks. In coco or hydro you should be providing nutrients (at seedling strength) from the very first watering because otherwise it only has the nutrients that were contained in the seed.

Nitrogen deficiency in hydro - caused by complete lack of nutrients (given just plain water)

 


 

More Examples of Common Cannabis Seedling Problems

 


 

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