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A Beginners Guide: NPK in Hydroponics

NPK Beginners Guide

NPK stands for nitrogen, phosphorus, and potassium. These three numbers represent the ratio of N, P, and K in your fertilizer. Every main mix (complete balance) fertilizer will have these numbers clearly displayed, always in the same order.

Not all fertilizers are complete balanced fertilizers, however. Different ratios of NPK serve different needs. For instance, a blooming mix might have low to no nitrogen in the mix.

So what do each of these nutrients do?

  • Nitrogen is what makes your plants green, big, and strong. It is the absolute most important nutrient in the solution.
  • Phosphorus is important for blooming; it plays a role in all of the reproductive roles of your plant.
  • Potassium is important to plant photosynthesis, CO2 uptake, activation of plant enzymes, and water uptake. It is important for building strong stems and seeds.

N, P, and K are not the only nutrient that your plant needs. Micronutrients are required in much smaller quantities. A complete and balanced fertilizer will almost always include the micronutrients.

The NPK in your fertilizer is not present in their pure elemental form. Plants can only take up certain compounds with these nutrients in them. Fertilizers also sometimes have multiple forms in the fertilizers. These are listed on the label of the formula.

A Word on Organic Fertilizers

Many sources of fertilizers are synthetically derived. You might be wondering if there’s an organic option. The answer is yes, but realize that more is needed to use an organic solution. To use organic fertilizers in a hydroponic setup, you need a very strong microbial community in your system. The microbes are what drives organic growing. They cycle the nutrients and turn them into a form that the plants can use. So if you don’t have a strong community, this won’t work.

Another drawback is that it takes time (6-18 weeks) to culture the microbial community.

A final drawback of organic hydroponics is that some solutions do stink. When you put a lot of organic compounds into water, you can end up with lots of anaerobic microbes that produce horrible smells.

If you’re using a solution with low nutrient, but not for a blooming crop, you should supplement nitrogen in another part of the solution. CaNO3, calcium nitrate can be used, to bring up the nitrogen ratios for our lettuce crops.

Please note that this site is supported by affiliate marketing which means that a small portion will be paid to maintain this site from any purchases made through it. This in no way affects the price of the products on this page.

Conclusion

Finding the right balance of nutrients for your plants is extremely important however buying pre-made mixes and following the very explicit instructions they come with will make the job a whole lot easier.  All of the products listed below come highly recommended.

Please follow and like my posts.  I would love to hear your opinion and ideas below!  Let’s keep the whole community blooming!


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Darlene Thompson

After having lived in Canada's most northerly territory of Nunavut where outdoor gardening is nigh impossible, I started down my adventure of indoor gardening. I hope you find the various methods as exciting as I do!

18 Comments

  1. Hi,

    Thanks for providing information about the science of hydroponics. My kids and I are into hydroponics at the moment and knowing what the Nitrogen, Phosphorus and Potassium actually do is going to be interesting for them.

    I’m looking to use organic fertilizers which I feel are safer to use than the synthetically derived ones. Can you recommend some organic fertilizers that I could buy online? I also need these to be able to be shipped to Australia

    • Hi Marketa!  You read my mind.  Although organic fertilizers aren’t actually any safer, there are still PLENTY of people that would like to use them.  This is a blog article in itself.  If you check back tomorrow, I will have that information up!

  2. This is extremely helpful for all the people that love planting and tending to their green thumb. I never knew fertilizer would be this helpful and what it would actually be made out of. My best friend loves tending to plants and wants have a garden in the future. I will definitely let him know about this awesome fertilizer post so he can keep them healthy. 

  3. Hi! You made me remember my high school classes 15 years ago. I had been asking myself what these three numbers represented and it’s nice to know it’s a really simple answer. These 3 essential macro-nutrients are everywhere in Hydroponics and it’s good I’ve started to realize where they’re indicated.

    • LOL – I agree.  SO many fertilizers just list NPK without telling you what each means.  I’m glad you liked this!

  4. Hi! Thanks for guiding us here to what each one of these 3 essential macro-nutrients do to our plants. I didn’t know that Nitrogen was the responsible for making our plants green. I thought that that was Phosphorus’ job but instead it’s in charge of blooming. This is really interesting. Thanks again.

    • Thank you, Abel!  Yes, many get confused as to what each letter means and what each does for your plants.  I’m so glad you found this useful!

  5. I just finished reading your post on Hydroponic Nutrients and decided to check out a few more of your posts here.

    Once again I find myself learning quite a bit.

    I didn’t realize that organic fertilizers required quite a bit more preparation and readiness than synthetic ones.  I’m thinking that I can start out with the synthetic setup and build that required microbial community before looking at an organic option.

    You’re just a fountain of information.

    Thank you,

    Scott

    • Thank you so much, Scott!  I’m so glad you found this and my other articles useful!

  6. Hello Darlene, thanks for this beautiful piece of information. Plants are very sensitive to nutrients provided to them and so its only advisable we are careful with what we apply to out plants. I am just learning about the NPK in fertilizer and also having a good knowledge of what they do in plants. I have been applying some fertilizer to my plants and it sad. I will look for these suggestions you have given here .

    • I’m so glad you found this useful, Benson!  It’s amazing what the correct nutrients in the correct proportions can improve your growing efforts.

  7. I think your site has a great layout. Great article, I found it very interesting to learn about the science of hydroponics. Very informative and great writing. And some good product picks. Keep up the good work. I think your menus are we’ll constructed. The use of the green background was a smart choice.

    • Thank you SO MUCH, Mark!  I truly appreciate your take on my site layout as well as the information provided.

  8. I am very grateful to have discovered the value you deliver here. As New Zealand gears towards making Cannabis legal I am trying to learn all I can to be ready. Learning about NPK sounds very crucial to the success and yields:) You have made it very clear and easy to understand. 

    Thank you so much

    Ropata

    • I’m from Canada and cannabis is now legal here so I certainly understand your excitement.  Frankly, many of my articles are for cannabis growing.  I truly believe in its healing properties and growing your own can be so very rewarding!

  9. I have suffered from plat lost in the past and my daughter’s favorite flower was included when this happened and it almost drove her interest in gardening away completely. This happened when I applied the wrong percentage of nutrients to my plants and the outcome was dreadful. It brings great joy to see a fertilizer with necessary nutrients for your crop and in the right quantity needed by plants.

    • Hi there, Bella!  Yes, you can kill a plant as easily by over-feeding as by under-feeding.  Even if you are using commercial fertilizers, be careful to follow the instructions that always comes with them as to dilution and such in order to achieve the effects you want

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