Cannabis Cultivation

Why are my Cannabis Seedling Yellowing?

A close-up of a young cannabis seedling with yellowing leaves. The plant is in a small pot, and the bright yellow contrasts sharply with the otherwise green environment.

In this article we will help you understand how to fix cannabis seedling yellowing. There can be many reasons why your cannabis seedlings are yellowing so we will break down why this could be happening.

Illustration-of-a-cannabis-seedling-where-the-leaves-are-turning-yellow-with-droplets-suggesting-overwatering

Why Bad Soil Causes Cannabis Seedling Yellowing

Starting your seedling with the right medium is essential to getting your new cannabis seeds off to a healthy start. Using soil or another growing medium that isn’t good for cannabis can cause your cannabis seeds not to germinate or die once they come out of the ground.

When picking a medium to start your seeds there are important factors to keep in mind that will keep your cannabis seedlings from yellowing later. You will want a good seed stating medium. This type of medium will be free of fungus and pests. Will be light and fluffy, will have excellent drainage for your young plants. This medium should be free of high nutrient content, if it has too much fertilizer in the medium it will most likely burn your new seedlings.

Cannabis Plant Yellowing

Not Watering Correctly can cause Cannabis Seedling Yellowing

One of the most common issues new cannabis growers‘ faces is failing to water there new seedling correct. The seeds and the seedlings require very little water when they first start life. Many growers will over water the seedlings. When this happens the seedling roots will be sitting in water for weeks at a time, there should be a wet and dry cycle. The wet/dry cycle allows for the seedling’s roots to uptake water, then dry out, causing the roots to grow out in search of more water.

If your cannabis seedlings are sitting in overly wet medium for too long it will cause the plants roots to get root rot. This will either kill the young plants or cause them to stop taking up nutrients and this is what leads to cannabis seedling yellowing. If this issue doesn’t get resolved it can also lead to a condition called damp off. This happens when the growing medium is confidently wet and is caused by a fungus that will attack the plant causing it to fall over and die.

Cannabis Plant Yellowing

Too Little Lighting for the New Seedlings

A detailed render showcasing a cannabis seedling situated in a shadowy spot, with just a sliver of light reaching it, highlighting the yellowing signs on its leaves.

Cannabis is a light loving plant. It will require a good amount of light as soon as the seedling breaks the soil. If your new cannabis seedling does get enough light right away, it can turn yellow and will slow die from a lack of lighting. It is also a great idea to provide enough like to new seedlings as they will stretch upward towards the light, in the case that the light is not powerful enough for them.

A photograph capturing a cannabis seedling in a dimly lit environment, showing the onset of yellowing leaves due to the lack of light.

Too Hot in the Grow Space

An artistic illustration presents a cannabis seedling inside a grow tent. Prominently, a thermometer is depicted next to the plant, displaying a notably high temperature, emphasizing the excessive heat in the grow space.

Extreme heat can cause the seedling to dry and the leaves to shrive and turn yellow first and then will die if the issue is not fixed. You will want to have good ventilation in the and a gentle fan blowing to keep the seedling cool, the fan breeze will also help to strengthen the new stem.

Your Growing Medium’s PH is incorrect

Vector-design-of-a-series-of-cannabis-seedlings-in-a-row-gradually-transitioning-from-healthy-green-to-yellow-indicating-various-stages-of-stress

Another important factor when selecting growing medium for your seeds is having the correct PH. If the PH is incorrect in the medium the plant will not be able to get the nutrients it needs right away. It the cannabis seedling can not take up the nitrogen that it needs to grow new leaves it can cause cannabis seedling yellowing on the leaves of the young plant. If you think you might have a PH in the medium that is out of range it may be best to purchase a PH meter to test your soil medium it should be in the range of 6.0 to about 5.7 range for seedling plants.

Over Fertilization can cause Cannabis Seedling Yellowing

Photo-of-a-cannabis-seedling-in-a-pot-with-visibly-yellowing-leaves-next-to-an-overturned-bottle-of-fertilizer-symbolizing-over-fertilization

Cannabis Seeds or young cannabis seedling require very little nutrients (Fertilizer) to grow. It is very common for new cannabis growers to give too much nutrients to a new plant fresh out of the ground. Most of the time this will cause the plant to get lock out (Plant will stop taking up fresh nutrients altogether) and the plant will start to yellow. This will lead the grower to believe that the new seedling needs more nutrients when in fact it will need to be flush of nutrients.

Cannabis Plant Yellowing

New Seedling Tip for Growers

Young cannabis plants need a very small amount of nutrients, most of the time these will be provided in the cannabis growing mediums for the young plants.  Typically, you will not have to add any new growing nutrients till the young plant has it third or forth set of fresh leaves.

The exception to this rule would be if you are using a medium that contains no nutrients. These types of plant growing mediums would include, but not limited to, Rockwool, Coco Coir, Rapid Rooters. These mediums will all require a small amount of full range nutrients right from breaking the growing medium.

Fixing Common Cannabis Seedling Yellowing Problems

Bad Soil

Vector-image-of-a-caution-sign-with-a-cannabis-seedling-icon-and-a-fertilizer-bottle-warning-against-overuse-of-nutrients-in-cannabis-cultivation

Take you young seedling an remove all the roots and as little of the bad soil/medium as possible. Dump out the bad medium/soil in the pot, clean the pot and add good fresh soil to the pot. Then place the young plant into the fresh soil/medium. Give the plant a couple of days to get adjusted before making any changes or adding fresh water.

Overwatering and Underwatering

A vector design vividly portrays a cannabis seedling under a powerful grow light. The seedling is surrounded by visual cues such as sweat droplets and wavy heat lines, indicating the extreme temperature it's experiencing.

If the plant is over watered, don’t water it till it is dried out. You can check our “How to water Cannabis Plants” for more detailed information on how to water your young cannabis plant correctly.

If it is underwater, it is best to give it some fresh clean water right away and monitor the plant to see if the plant leaves perk back up. This normally takes and hour or two to happen, so you will need to give it some time.

Too Little lighting

Render-of-a-cannabis-seedling-placed-on-a-sunlit-windowsill-during-a-hot-summer-day-with-its-leaves-showing-signs-of-yellowing-and-stress

You can look to move the plant light closers being careful not to move it too close and burn the small plants. You can also add new lighting to supplement your current lighting.

Too Hot in the Grow Space

Photo-of-a-cannabis-seedling-under-intense-heat-with-a-heatwave-visual-effect-and-the-leaves-starting-

The seedling room temperature should be between 70F (21C) and 80F (27C) for the best growth. If it is consistently over the high temperature, you will need more ventilation or if this doesn’t bring down the temperature you may need to invest in Air Conditioning for your grow space.

In Correct Medium PH

First check with a meter that this is in fact the case. If it is out of range, you can use PH up or PH down to adjust the water to bring the growing medium into the proper range. If you are unable to do this you may have to change out the medium using the steps in “Bad Soil” above.

Fixing over Fertilization

An illustration that contrasts a healthy green cannabis seedling with a yellowing seedling. Positioned behind the yellowing seedling is a large sack of fertilizer, emphasizing the notion of excess fertilization.

Take your seedling container and using clean fresh water. Take the water, run it over the plants medium for a few minutes to flush out an excess nutrient. Give the young seedling a chance to recover over a couple of days. The leaves should start to green up. If this doesn’t happen this may not have been the issue, or you will need to flush the plant again.

We hope this article will help you to find the cause of your cannabis seedling yellowing.

If your are looking for great cannabis seed strains check out this article!

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