• Ali Bongo, Head Shop UK, buy best bong UK, Percys Grow Room
Clear all

[Sticky] Phosphorus Deficiency

100 Post Likes
250 Post Likes
500 Post Likes
Respected Member
Points: 12427
Posts: 162
Topic starter
Joined: 3 years ago

Phosphorus is the “P” in your N/P/K Ratio. Like Nitrogen and Potassium, it is known as a “Macro nutrient”, and is one of the three main elements needed in plant growth. A phosphorus deficiency can have a big impact on your plant development, especially during the flowering period.

Phosphorus is like a power line, connecting all of your plants cells together. The energy created by the plant via photosynthesis, is transported around the plant using phosphorus. It is also a major element in flower, and root growth.

Because flowers are also built out of phosphorus, you will find bloom foods, and P/K boosters will be high in phosphorus.

If you think you have a phosphorus deficiency in your cannabis plant, then feel free to ask for help in our cannabis growers forum

The Effects of Phosphorus Deficiency in a Cannabis Plant

Phosphorus is used by the plant transport energy from one place to another. If there isn't enough of it available to your plant, it will grow slowly, and become weak. Also, if you're in the flowering stage, your flowers will not form and grow to their full potential.

What Phosphorus Deficiency Looks Like

A brief Description of Symptoms of Phosphorus Deficiency in a Cannabis Plant. Percys Grow And a Cannabis plant drawing with dark green leaves How to grow legal cannabis, a step by step guide to growing weed, cannabis growing guide, tips for marijuana growers, growing cannabis plants for the first time, marijuana growers forum, marijuana growing tips, cannabis plant problems, cannabis plant help, marijuana growing expert advice.

Plants need a large amount of phosphorus to grow, healthily and happily. Without the right level, leaves will be small and have a blue-green colour. Stems of the leaves may turn purple. Starting with older leaves first and moving onto the newer leaves in bad cases. In extreme cases, your leaves develop purple or black blotches, and fall off.

Because phosphorus is used a large amounts to build flowers on your cannabis plant, a deficiency will reduce the rate of your bud growth. To make sure you get the best harvest possible, you need to keep your phosphorus levels in check.

How to Fix Phosphorus Deficiency in a Cannabis Plant

A cannabis leaf effected by phosphorus deficiency. yellow edge with brown blothces

It will depend on what medium you're growing in, but these problems are easily fixable! With any deficiency, it can be one of two things, either, a; your medium does not have enough phosphorus in it that is available to your plant. Or b; the PH of your medium if off, and needs restoring so it is within the correct range.

Phosphorus Deficiency in Coco & Hydro

Increasing the EC of your feed is a good way to add the extra phosphorus to your medium. Bloom nutrients, are high in P, and will be an easy way to fix the problem.

Increasing the EC of your feed by 0.2 points, every few days, will bring the correct level back to the plant. Be careful not to go too high. Gradual increases are important, and you must read the plant and the EC of your feed and run off. As soon as it looks healthy again, stop increasing the EC.

A PH imbalance can always be the cause of any nutrient problem! So make sure your pH is set to 5.8-6.2 in any hydro or soil less medium grows.

Phosphorus Deficiency in Soils Grown Cannabis Plants

If you’re using salt based nutrients in your soil, then increasing your EC for a couple of feeds should fix the deficiency within a week. If you’re growing cannabis organically, there are many things you can add to the medium, to increase the phosphorus content. 

Bat guano is amongst the favourite organic phosphorus heavy food sources. It will also improve the flavour of your final product. Simply top dress your medium and water it into your plants. It will help the roots grow stronger, and buds grow fatter.

Alternatively, Bone Meal is another great sources of organic phosphorus. Be careful when using any nutrients. Too much can quickly damage your roots, and will do more damage then the deficiency would! Look out for signs of excess. If you do go over, and the plant starts to show sign of P excess, Check out this guide:

Phosphorus Excess

One more thing

You can easily come a cross a P deficiency by over watering your plants! Make sure you are watering your plants correctly! Each medium has their own specific watering schedule, coco, every day is best, soil, when the pot feels light. More info on how to water you cannabis plants correctly can be found here:

Thanks for reading! You can find more information on anything related to growing in our cannabis grow guides. All of our guides are written by experienced growers, and members of our cannabis growers forum. If you have any questions, sign up. It is free, and we are always happy to help!


In our cannabis growers forum, we have guides to growing cannabis, cannabis grow dairies that cover growing weed in hydroponics, soil and coco. Find the help you need, by either, using the search box, or asking for help in the forum.

Our cannabis growers website also has competitions where you can win free weed seeds. As a member you will also have discount codes for cannabis seeds, and LED grow Lighting.
Our Cannabis Growers Forum is for educational purposes and we encourage our members to check their country of residence legislation before germinating a marijuana seed.

This site is here because we want to help you grow your own cannabis for personal use. Therefore, any member who is suspected of growing cannabis for commercial gains will be banned immediately.

Please read our forum rules, and enjoy the site.

Percys Grow Room Facebook Page, Cannabis grower forum fb page,
percys grow room twitter icon, cannabis growers forum
pintrest logo percys grow room, cannabis forum
percys grow room instagram logo

Find us on all social networks! Just search for Percys Grow Room

Percys Grow Room