npk levels for growing weed

Ideally, cannabis growers should gradually alter their NPK values, which means using a ratio of 1:3:3 in early flowering and 0:3:3 in late flowering. Nitrogen should be completely absent from the mix for at least the final three weeks of the bloom period.

Choosing a product with the correct NPK ratio is vital for cannabis growth. During vegetation, plants need lots of nitrogen to produce all their green parts like leaves and stems. Cannabis plants generally benefit from an NPK ratio of 3:1:1 at this point in their lifecycle, ensuring they receive plenty of nitrogen and just a little of the other two nutrients.

Meanwhile, sea kelp and wood ash are both high in potassium and are fantastic tools for adjusting your cannabis plants’ NPK ratios.

Ready-made plant feeds and fertilisers with set NPK ratios can be bought from most garden centres and applied to cannabis plants with minimum fuss. Granular feeds are the most common, but liquid and gaseous products are available too.

Other sources of nutrients include human urine and animal manure, both of which are high in nitrogen and should only be used during the vegetative stage. It’s not wise to pee directly onto plants as there’s a lot of salt in urine. Instead, it’s advisable to dilute your pee in the water, using twenty parts water for every one part urine.

The Importance of NPK for Cannabis.

When the flowering stage begins, the NPK balance should switch in favour of phosphorous and potassium. The former helps plants produce large buds, while the latter allows flowers to increase in size. Too much nitrogen can be detrimental at this time, as it prevents flowering and can leave your bud with an unpleasant taste.

Cannabis plants require many nutrients, but nitrogen, phosphorous, and potassium are the three most fundamental elements in a plant’s diet.

The value for nitrogen coming first and potassium coming last.

Bone meal and fish meal are excellent sources of phosphorous and are popular among gardeners. These can be scattered on the soil around a plant’s roots during flowering to bring NPK ratios up to the ideal value for cannabis.

Most high-quality soils contain plenty of nitrogen. It may not be necessary to add any of these key nutrients during the first month of growth. When growing in low-quality soils or other growing mediums, though, it’s essential to give your cannabis plants the nutrients they need.

Most fertilisers and plant feeds contain NPK values on their labels. These appear as three numbers denoting the relative concentration of each component. For instance, a ratio of 2:3:8 indicates that a product contains two parts nitrogen to every three parts phosphorous and eight parts potassium. Cannabis growers should be aware that NPK ratios always appear in this order.

Known by their chemical symbols N, P, and K, these three nutrients are essential for healthy growth. As cannabis plants move from the vegetative to the flowering stage, the ideal NPK ratio shifts. Meaning growers need to adapt their feeds and fertilisers.

Finally, growers should be aware that the pH of their soil affects plants’ ability to absorb these nutrients. Cannabis plants can therefore suffer nutrient lockout even when NPK ratios are ideal. It’s vital to ensure that soil acidity falls within the optimum range of between 6 and 7.

Related Post.

How To Apply NPK To Cannabis.

Potassium helps the plant as an auxiliary nutrient. It regulates the systems needed to stay healthy and to grow. Potassium ensures firm stems as well as stimulating ATP production needed for energy storage. It is also important for a strong immune system. In addition, potassium plays a part moisture evaporation through the leaves. It ensures proper balance of salt and water concentrations, and it is critical to sustaining a functioning sap flow throughout the plant.

Providing just the right nutrients is a veritable art form. Give too much and you’ll harm your plants, or even kill them. The safest approach is to start out at 25% of the recommended quantity stated on the package, and then to gradually increase to the full dose.

Phosphorus deficits are expressed by underdeveloped root systems, leading to stunted plants. The flowering phase of a cannabis plant is where lack of phosphorus really sticks out, though. To all probability, the plant won’t be able to flower at all. An early warning sign of phosphorus deficits is a purplish colour of the leaf veins.

Potassium (K)

So with these NPK facts out of the way, let’s head for the Amsterdam Genetics Seeds range and see which strain deserves all those lovely nutrients the most!

Providing your pants with these three essential nutrients is a key part of growing cannabis. Nitrogen, potassium and phosphorus are commonly sold as soil fertilizers named N-P-K. This formula usually states three figures indicating the percentages of each nutrient in the mix. 10-4-4, for instance, means 10% nitrogen, 4% phosphorus, and 4% potassium.

Growing weed in soil is completely different from growing on hydroponics. Plants with their feet in the earth benefit from all the available nutrients already contained in the soil. Humus, organic fertilizer, compost, and countless micro-organisms are already working to keep the soil balanced. That means many of the essential nutrients will be available by default. These substances are not soluble, however, so microbes and fungi are needed to convert them into form usable by plants.

If cannabis plants are grown using hydroponics, nutrients come in liquid or powder form. These concentrated minerals have to be dissolved in water before the plant can absorb them. Liquid products are sold as two separate components A and B. When these are added to water, all nutrients become available to your plants.

Cannabis grown in soil can still benefit from added nutrients for health support. Liquid fertilizers used for hydroponic grows are not essential. Most soil types contain plenty of nitrogen to see your plant through.

It’s a good idea to keep track of these NPK percentages. Cannabis plants will need different ratios in every stage of their life. Product packaging usually indicates the particular stage for which fertilizers are intended (growth or flowering). In the growth or vegetative phase, weed plants need more nitrogen, whereas they can use more phosphorus and potassium while flowering.

All growth depends on the right nutrients.

Nitrogen, Phosphorus And Potassium For Various Growing Methods.

Potassium is also crucial throughout the flowering phase, to control flower bud formation. Weed plants need it to keep cell pressure steady, protecting the plant from drought. This mineral is also important for the formation of a strong root system.

Phosphorus is key to growing strong roots.

Growing cannabis can be approached in various ways: in full soil, in pots, or using hydroponics. Growing with hydroponics means raising your plants not in soil, but in a basket or pot filled with a growing medium (like coco fibre, clay pellets, or rockwool, for example). Each growing method requires different nutrient regimes.

Nitrogen (N), phosphorus (P), and potassium (K) are so-called micronutrients. Your cannabis plants need all three (and more besides) to unleash their full growth potential. Paying attention to micronutrients is important, because plants need different nutrients in different quantities as they pass through the various stages of their life cycle. In this context, ‘NPK’ is a famous grower abbreviation. That’s because together, phosphorus, nitrogen, and potassium stimulate root system formation, absorption of other nutrients, and many more crucial processes. Knowing a weed plant’s favourite food allows growers to give them all they need to enjoy a bountiful harvest.

However you grow, get your NPK sorted!

Phosphorus (P)

In case you’re wondering, NPK servings can be kept completely organic for natural results. The BIO PK liquid you’ll find in our webstore contains a careful balance of fully organic nitrogen, phosphorus, and potassium. That’s an efficient, fast growth or flowering booster for any cannabis plant, regardless of the strains or soil types you prefer.

Potassium deficits become apparent in weak, low-energy plants. The first sign is usually leaves with yellow edges. A plant lacking in potassium is unable to regulate exchange of CO2, oxygen, and water. This results in thin, stretched plants with stems too weak to support their branches.

So how do you know whether cannabis plants are suffering from nitrogen deficits? You can tell by discoloration of the oldest lower leaves. This is because nitrogen is a nutrient that can be relocated throughout the plant. If there is a lack of nitrogen when new leaves are formed, nitrogen stored in the older leaves is used instead. This causes the lower leaves to turn yellow and fall off eventually. Nitrogen deficits are also apparent in slow growth. The plants may weaken and become susceptible to disease and pests.

Nitrogen is the most common element in the earth’s atmosphere. Together with is carbon, hydrogen, and oxygen, nitrogen is also the most common element in organic lifeforms found on our planet.

Nitrogen is called a primary micronutrient. Not very surprising, as this substance is vital during both the growth and the flowering stages of all plants. Basically, this element is crucial throughout all stages of the life cycle of cannabis plants. Nitrogen is used for production of chlorophyll. This compound gives plants their green colour, as well as being a key component of photosynthesis: the process in which a plant converts sunlight into plant energy supplies.

Phosphorus is necessary during the flowering phase. This micronutrient’s job is to make other nutrients available for the plant, allowing it to absorb them. Phosphorus is used to fortify the plant’s structure, from the roots to the flower buds. It is necessary to promote the overall health of your plant. Phosphorus makes a plant appear strong and vibrant. Germination of seeds depends on phosphorus, too.

After a week of flushing, the plants should be given no more water. After 4-5 days of drying out, leaves the plants in the dark for 24-48 hours before cutting it down. This will help rid the plant of chlorophyll and will prompt the plants to produce resin. This final drying out and dark stage is what helps the flowers turn into nice, dense sticky buds.

Once the cannabis plant has 5 bladed leaves it enters early vegetative stage. Planted clones also are considered to be in early vegetative stage. Cannabis plants in this stage can move up to a mild feeding, about ½ of the recommended amount in addition to Root Juice.

Mid flowering stage begins once the stretch is complete. This is the most crucial time for feeding in order to create big, dense flowers and buds. Cannabis plants want lots of Phosphorus and Potassium in this stage. A very popular additive is PK 13-14, which is high doses of Phosphorus and Potassium with no Nitrogen in the solution at all. The plants still need Nitrogen so don’t forsake it completely. However the PK 13-14 additives allows you to boost the PK ratios as it is difficult to find over the counter fertilizer with very high concentrations of Phosphorus and Potassium.

Recognizing that the needs of the cannabis plant changes over the different stages of its life is really the key to growing the best flowers. The idea is to feed the plant the food it needs at that time in its life. If you were to feed a cannabis plant the same food mix for its entire existence you will probably grow something, maybe even something decent, but you would never grow the highest quality cannabis.

The final stage is a flush. We want to get all the chemicals out of the plant to improve the taste and quality of the smoke. Thus for the final week, the plants get only water. This is true for both feminized and autoflowering cannabis plants.

Change From Vegetative to Flowering NPK 7-7-7.

The key here is to recognize Potassium is always about 65% of the main element, Nitrogen during vegetative and Phosphorus during flowering. Also that the “weakest” element is always about 50% of the main element. Thus the correct ratios look something like this: Vegetative NPK – Nitrogen is the main element.

Flowering NPK – Phosphorus is the main element.

Very simply, during vegetative, Phosphorus should be about 50% of Nitrogen, while Potassium is about 65% of Nitrogen. During flowering, Phosphorus is the main element, while Nitrogen is about 50% of Phosphorus, and Potassium is about 65% of Phosphorus (with the exception of mid flowering when it is boosted to be about equal to Phosphorus).

Reduce the nitrogen and increase phosphorus and potassium to create a balanced NPK. This can be done by mixing grow and bloom formulas. The goal is to make a stress free transition from vegetative to flowering stage. Radically changing a cannabis plants’ feed can induce stress on the plant and any stress normally stunts growth.

Nitrogen (N) : Nitrogen helps in making proteins that are used for foliage growth. Excessive Nitrogen will cause fast growth but poor flowering, . A Nitrogen deficiency causes stunted growth.

Cannabis, like all plants, has a ratio of NPK that helps it grow strong and healthy. Just like people, different plants prefer different diets. And just like people, the preferred diet changes as the plant ages. By understanding cannabis NPK, you can adjust the feed to produce a healthier, higher yielding plant.

Cannabis plants, like all living things, need food to grow. For most people this involves soil, water and fertilizer or plant food. But growing cannabis is not as simple as watering and adding any old fertilizer, at least not if you want to grow good cannabis. Understanding NPK ratios and when an autoflowering or feminized cannabis plant requires different nutrients is what separates a good crop from a fantastic crop.

As the pistils start to change to a higher ratio of red/brown and fold over, the cannabis plant is entering late flowering stage. It is time to reduce all NPK and start to wean the plant off the food. As the ratio of brown pistils start to approach 60%-70%, the cannabis flowering stage is beginning to come to an end.

A seedling is stage between germination and the first 5 bladed leaves, typically found at Node 3. A node is simply a pair of new branches/leaves. Node 1 normally has single bladed leaves. Node 2 has 3 bladed leaves. This sequence continues up to 7, 9, 11, and even 13 bladed leaves. The key is that seedling stage ends after node 3 and the pant enters early vegetative stage.

Phosphorus (P) : Phosphorus is key to strong root growth, flower development and larger seeds. An excess of Phosphorus causes poor growth and bleached or yellow leaves. A phosphorus deficiency causes leaves to die.

Early Flowering 5-10-7.

Late flowering lasts 2-3 weeks in feminized plants and 1-2 weeks in autoflowers.

As the plant hits nodes 5 and 6, the plant is in vegetative stage. Cannabis plants want a lot of Nitrogen at this stage to help grow strong and healthy. Root Juice can be continue to be added until late vegetative stage. At the end of the vegetative stage, Root Juice is no longer needed, and the plant should be prepared for the changeover to flowering. Start to reduce Nitrogen levels at this point.

Nitrogen is still being reduced. Potassium is being held firm while Phosphorus is still increasing. Cannabis plants want and need Phosphorus to grow flowers. The early flowering phase is roughly 2 -3 weeks for feminized plants, but only 1-2 weeks for autoflowers. This early flowering stage is accompanied by the plant stretching, or growing taller quickly. Once the plant stops growing taller, the stretch and early flowering stage is completed. Flowers should be entirely white pistils.

More important than trying to follow this NPK guide perfectly is to recognize the key is in the ratios between NPK than the numerical amount(ie 7-7-7). Keeping the correct ratios is more important than the concentration. So for the change over stage, feeding 5-5-5 is perfectly fine. It is not the recommended 7-7-7 but the ratios between NPK are the same. However you would not want to feed the plant 9-5-9 as the ratios between N, P, K are entirely different when compared to 7-7-7 or 5-5-5/

There are other nutrients and compounds that a plant needs, but they are often required in tiny amounts. Calcium, Magnesium, & Iron are needed by plants, but in minuscule amounts compared to NPK.

A seedling requires very little feeding. Starting at ¼ strength of whatever is recommended and only every 2nd or 3rd watering. Most seedlings should be able to draw from the soil whatever nutrients they need. Adding a little Root Juice to help the roots grow is always a good idea.

Potassium (K) : Potassium is important for overall plant health and development of flowers. Excess Potassium can cause (N) and (P) uptake to be blocked which would then lead to (N) & (P) deficiencies and issues. Potassium deficiencies lead to disease and overall poor plant health.


Mid flowering stage ends once pistils are beginning to turn brown/red. Mid flowering is about 3-4 weeks in feminized plants and 2-3 weeks in autoflowers.

NPK are the chemical symbols for Nitrogen (N), Phosphorus (P) & Potassium (K). These three elements are found in almost every type of soil sold are the amounts are normally listed on the bag or bottle under the NPK designation. For example, if a bag of soil is 15-18-20, it is referring to the ratio of NPK. The same is true on a bottle of fertilizer. The ratio of NPK will normally be listed somewhere on the label.

With the above Cannabis NPK Chart you should be well on your way to growing healthy, strong and high yielding cannabis plants. With a bit of trial and error, you should be able to provide the feed your cannabis plants want, when they want it. The end result of good feeding is big, fat, sticky, dense buds which is the goal for every grower.