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The Importance of PK Nutrients

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Cannabis plants have quite a specific diet, and three of the most important nutrients that they need are nitrogen, phosphorus and potassium, which are fundamental for your plants to grow properly and develop its flowers. The combination of these three nutrients is incredibly important when it comes to growing cannabis in its different stages; today we’re going to have a closer look at PK nutrients, which are needed most during the flowering period.

PK is an acronym given to two chemical elements, Phosphorus and Potassium, which are the two main nutrients needed when it comes to fattening cannabis buds.

Phosphorus is involved in resin yield and seed production during the flowering period, although during the growth period it’s used in the photosynthetic process. PK nutrients tend to contain high amounts of phosphorus in order to improve your plants’ metabolism.

On the other hand, potassium allows your plants to grow their roots out during the growth period, as well as growing thicker stems and branches. During the flowering period it increases terpene and essential oil yield, which increases flavor intensity in your cannabis plants.

When should you start using PK nutrients?

Knowing exactly when you should use your PK nutrients is a question that growers come to us with almost daily. If you can figure out when the best time is to start using these products, you can increase your yield quite a lot, as well as resin and terpenes.

You should start using these additives once your plants begin to form their first flowers during the flowering period. Your plants will stop growing upwards and start paying more attention to creating brand new flowers and fattening them up. You’ll need to have fed your plants properly during the growth period in order for them to flower healthily, however. The stronger the plant structure, the heftier and larger its buds can grow.

If you want us to give you an exact week or day that you’ll need to start using PK nutrients, you’re out of luck. This strictly depends on the product used and the amount of PK in each product. Generally, we start using PK from the second flowering week onwards, as well as the rest of your necessary additives and stimulants. Although, if the PK product that you plan on using is highly concentrated, you should probably use it further on, towards the end of the flowering stage.

These fattening products are perfect if you want to harvest delicious, thick, aromatic and resinous flowers from your cannabis plants.

Types of PK nutrients:

There are an incredible amount of fertilizer brands on the market that have spent a lot of time developing products that increase yield from cannabis plants. There are two types of PK nutrients:

  • Chemical
  • Organic

The first type, chemical fertilizers, are mineral in origin and are mainly made by the fertilizer industry. These products come in both solid and liquid format, and are generally used by beginner growers that are looking to get amazing results right from the get-go. They’re also used quite a lot by growers that want to produce a lot of flowers for commercial reasons, as they can thicken up buds in no time. One of our most sold chemical products is Big Boom PK 52-34, which is the highest concentration of phosphorus and potassium, allowing you to double the size of your flowers.

When it comes to organic products, they usually come from plant extracts or animal extracts. They’re the most sold nutrients when it comes to homegrowers. They’re usually full of nitrogen, phosphorus and potassium, as well as smaller trace elements. These nutrients are used to stimulate your plants to generate more terpenes and sugars, which increases the size of your buds while keeping them proportionately dense. We have products such as Bio Bloom by Biobizz and Top Bud by Top Crop, two natural fertilizers used to fatten buds with 100% organic results.

How to use PK nutrients

Fattening products for cannabis plants, like we said before, are generally used at the start of the flowering period. This can vary from the 2nd to the 4th week depending on the manufacturer and the PK content of the product being used.

In order to use these products correctly you should follow the manufacturer’s instructions, although generally speaking PK products are used once a week. This is due to the fact that they’re highly concentrated and your plants need time to metabolize their ingredients – in some cases you can use the product more than once, but only if the manufacturer specifies it.

Not all PK products on the market provide the same results for all growers, however. The amount of experience you have growing is incredibly important, as you need to be capable of picking the right substrate, as well as monitoring pH and EC – this is especially true when it comes to Big boom, which requires you to run a tight ship.

Also, you should keep in mind that you should always flush your plants’ roots before harvesting, around 1-2 weeks before harvesting; your plant will accumulate salts that you’ll need to remove by washing the roots out using just water or a product made specifically for this purpose.

What are the best PK nutrients?

If you do a quick search you’ll see that there are an incredible amount of PK nutrients on the market, and we’ve written an article that deals with what we consider to be the best organic and mineral PK products on the market; How to Grow Bigger Buds on Cannabis Plants.

Some of the most sold PK products on are Big Boom PK 52-43 , Super Bloom and Monster Bloom. These three chemical fertilizers have incredibly high amounts of phosphorus and potassium that’ll absolutely explode your plants’ flowers.

When it comes to organic fertilizers, our customer-favorites are Bio Bloom by Biobizz and Top Bud by Top Crop, as well as Guano by Guanokalong and Bio PK 5-8 by Bio tabs. All of these organic products also give your plants a little extra boost in as far as flavor and aroma thanks to their 100% organic ingredients.

Which one is better, though, organic or mineral? I guess that’s up to you, whichever one gives you the results that you’re looking for. Experience is key.

What do PK nutrients actually do? When should they be used? How many types of PK products are there? Discover everyting you need to know & more, right here!

The flowering stage

The plant is fully grown and the end is nearly in sight. Now we are approaching the flowering phase, after which you can start harvesting. The first three weeks of the flowering stage are in fact more a growth phase. After the flowering period of the plants has been initiated by setting the lighting to a schedule of 12 hours light and 12 hours darkness, they will start flowering and buds will start growing explosively. In which week of flowering do the buds grow most depends on the strain and type of cannabis plant you are growing. They can easily double or even triple in size. I remember the first time I ever grew a plant as if it was yesterday. I was amazed to see that the little plant quickly transformed into a giant. The buds keep swelling, the trichomes start being formed and the specific odor of the plant continues to develop, which makes it hard to wait until the buds can be harvested and you can enjoy the first joint of your own harvest.

Grow and bloom fertiliser

During the flowering phase, you have to switch to bloom nutrients. Some growers keep giving their plants grow fertilizer in the first and sometimes in the second week of the flowering phase because it is a kind of transition period and the plants still need building blocks to grow quickly. This will make the plants grow a bit taller. It all depends on what you want. By managing your use of fertilizer, you can control the size of your plant. If your plants already have the right size and you want to keep them smaller (because for instance space is limited), immediately start giving them bloom fertilizer. If your plants are still a bit small and space is not used optimally, you can continue administering grow fertilizer. They will grow a bit taller. The differences are not extreme, but a couple of centimeters can make quite a difference.

Bloom nutrients

After a blooming period of three weeks, the plants have achieved their maximum size. They will no longer grow in height and width but will start forming buds. It is really important to administer blooming nutrients then because the plants need more phosphorus and potassium. These are important building blocks for a good bud formation. PK 13/14 is a mixture high in phosphorus/potassium that stimulates flowering and fruiting. It is usually indicated on the bottle how much you have to administer. Make sure you do not give the plants too much, otherwise you risk overfertilizing them.

Suzy’s Tip: Watch your plant closely and try to tell what it needs. Every plant blooms in its own way, so in some strains, the buds will grow from the beginning, while in other strains they will only grow in size and weight in a later stage. The needs of the plant can also change after a couple of weeks.

Foliar feeding

If you fertilize well, you actually don’t need foliar feeding. Unfortunately, it is very hard to fertilize flowering cannabis well. Even if you think that you are giving the right nutrients, the plants may lack something. If so, you can administer foliar feeding to your plant. The nutrients are rapidly absorbed in this way and any nutritional deficiencies are corrected quickly. The chance of overfertilizing is minimal when administering foliar feeding. When growing inside, the best moment to administer foliar feeding to your plants is half an hour before the lamps go on. The light of the lamps is very powerful from the beginning, so you run the risk of burning the leaves if they are still too wet. Outdoor plants are best being administered foliar feeding early in the day, before the sun is too strong. It’s no use giving them feeding when there is no light because then the plants don’t grow and they don’t need extra feeding. Besides that, you increase the risk of mold if they are too wet. Foliar feeding has to be sprayed on top of the leaves, once or twice per week. When giving foliar feeding, you also have to watch your plant closely to discover which nutrients it needs.

Top/tie down

If space is limited, you might want to top or bind down your cannabis plants. Topping is removing the top of the plant. You will get two main tops instead of one. These do not grow as tall as one top but they yield more. You can bind a plant down by pulling the biggest bud down and binding it with slight tension. This will give you the same effect as topping, but you have the advantage that the largest bud is retained. The lower branches will develop better and the plant will grow bigger buds.


For a good flowering period, the plants need sufficient CO2 (carbon dioxide). They need this to grow powerfully during the hours that there is light. The more CO2 is present in the air, the faster the plants will be able to develop and the better they will be able to withstand high temperatures. You can use fans, but in good growing spaces, holes are made in the ground at one side to let air in, while at the other side an extraction system is installed as high as possible. This ensures an optimal circulation of air, from which the plants benefit by using the CO2-rich air that is continually circulating. Fresh air is continually sucked in through the holes in the ground. A fan is also very important. These do not only ensure good air circulation but also give the plants a pleasant breeze which will cause them to grow even better.

Bud formation

The period in which the buds of your cannabis plant start growing quickly is the most important in the flowering period. Depending on the strain, that’s usually after about 3 to 5 weeks also called the end of the flowering period. You can continue spraying your plant until then because the buds have not yet become hard and compact, but you shouldn’t after that. So you can opt for preventatively spraying your plant. When the buds start growing rapidly, you can’t do much more than administering nutrients and enjoying the wonderful sight of the buds that are gradually being formed. More and more white hairs will grow and the separate little buds will steadily grow inwards to form one big bud.

The flowering stage of the cannabis plants starts by setting the lighting to 12/12 hours light/darkness. As soon the flowering phase starts the buds will begin to develop.