Why Are My Plants Turning Yellow? - Nitrogen and Cannabis Plants Explained

In this article, I explain why Nitrogen is so important when growing cannabis, why cannabis plants leaves turn yellow,  the list of organic sources of  Nitrogen that can be used, as well as my top tips to consider making

What causes cannabis plants to become Nitrogen deficient?

During a cannabis plant’s various stages of its lifecycle, it will use a wide range of nutrients accordingly. These will cover the primary nutrients (NPK) and the secondary nutrients (Ca and Mg) and trace elements. Nitrogen is one of the only nutrients that when it is running low, it will actually transfer the available Nitrogen from one set of leaves to another. 

As cannabis plants are able to produce an abundance of fan leaves and smaller leaves during the vegetative and flowering stage, keeping the optimal balance of Nitrogen will ensure the foliage is bright green, soft to touch and the leaves are as healthy as possible. 

The main reason why a cannabis plant will begin to turn from green to bright yellow then fade to a lifeless pale yellow is due to the demand of metabolism and growth. Fast growing plants that are under high intensity lighting will often require more Nitrogen that a young plant that is kept under soft lighting such as CFL or a low powered LED.

The benefits of growing Nitrogen rich plants

• Cannabis plants will grow with a bright green, waxy characteristic and be full of vitality.
• Fan leaves act as solar storage units so the bigger the leaves, the better for the plants.
• Clones will not show any signs of yellowing or struggling to root when plants are healthy.
• Other deficiencies will not start to appear ensuring the plants are green and bright coloured.

Organic solutions to provide more Nitrogen

If you are an organic grower and are looking for a good solution to keep your cannabis plants well topped up with ready to use Nitrogen, then below is a list of all the available options to consider.

Compost

The great thing about compost is that it acts as a slow release organic amendment, so is an excellent way to keep the Nitrogen levels of your crop nicely topped up. Compost also releases other trace elements and particularly rich in Magnesium.

Blood meal

Basically dried blood often sourced from slaughter houses, however is very rich in only Nitrogen so a great way to keep the phosphorus and Potassium levels as they are. 

Manure

Manure is similar to compost in the fact it slowly releases nutrients, and is also great for promoting beneficial bacteria and microorganisms.  Manure does not contain high levels of NPK but can work well for restoring plant health and vigour.

Bat Guano

Depending on where the bat guano is sourced from and the diet of the bat, can make a Nitrogen rich bat guano that can be used for the vegetative stage as a Nitrogen boosting agent. Usually bat guano is used to promote flowering, however combining a Nitrogen and Phosphorus rich guanos together would be well advised. 

Liquid seaweed

Seaweed is a great way to feed your plants and give them a tonic packed full of nutrients. Liquid seaweed contains auxins, cytokinins, natural growth regulators and is a great way to supplement plants with Nitrogen. Foliar spraying seaweed at a ratio of 1-2ml per liter will feed the plants through their leaves and promote healthy growth. 

Fish emulsion

Quick to break down and full of nutrients, fish emulsion can be used at all stages of the plant’s life to boost Nitrogen levels and provide an abundance of trace elements. Be Careful using fish emulsion outdoors due to animals digging up the soil looking for food!

Chicken manure

Manure taken from chickens that has been left to age long enough where it will not burn plants, is another wonderful way to keep the NItrogen levels at peak. Chicken manure does not contain alot of NPK, so can be used frequently as a top dressing.

Worm castings

Orms are Nature’s little helpers an as they eat their way through organic material, they excrete a microbe rich bi-product which contains all of the nutrients a cannabis plant needs. Worm castings can be mixed with old soils to boost the microbiology and also enhance how fertile the soil is. 

Coffee grounds

Now you may be thinking coffee grounds, but believe it or not they work a treat at releasing Nitrogen back to the growing medium. Coffee grounds also lower pH levels making them a good tool for naturally lowering pH and growing organic cannabis.

What to do with yellow and brittle leaves

There are times when yellow and brittle leaves are ok, however knowing when you should have lush green plants or yellowing leaves, can come down to the different stages. Below is a break down of what to do during 18/6 and 12/12 with lifeless leaves.

During the vegetative stage (18/6) - When you notice that your fan leaves are turning light yellow and are brittle and delicate to touch, you can simply pluck those leaves off and do your best to not let other leaves start to show signs of yellowing due to developing Nitrogen deficiency. 

During the flowering stage (12/12)

The time to cut Nitrogen off during the flowering period should be as you approach week 4-5, and allow the Nitrogen to be used up. Yellowing fan leaves that fall off are a sign that the plants are no longer focusing on photosynthesis, and are at the end of their lifecycle, whilst plants focus on Phosphorus, Potassium, Calcium, Magnesium and the trace elements during bud production. 

My final thought on Nitrogen and cannabis plants

Nitrogen is one of the main nutrients a plant needs and as long as there is a consistent amount readily available to them, there is no reason why a plant should use up what is available too soon, and start yellowing. 

Using compost, manures, blood meal, bat guano, fish emulsion and seaweed and worm hummus is a great way to produce a microbe and fungi rich environment, and also produce some incredible tasting organic cannabis. Be careful using chemical Nitrogen feeds sold at gardening centres and also read the label when buying complete soils to check if they use chemical Nitrogen or organic sources.