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NPK and Other Hydroponics Terms Explained

NPK and Other Hydroponics Terms Explained

Horticulture, hydroponics, and plants in general can seem very mysterious with all the technical jargon, ratios, fluxes, etc. So here’s a quick list of common terms, and the science behind them, that will help you decipher all the plant prattle out there as you get started with hydroponics

What is N-P-K Ratio?

Any time you pick up a fertilizer, be it dry or liquid, you will notice 3 numbers separated by dashes somewhere on the packaging. This is the N-P-K ratio. Each of these numbers represents the percentage of a particular element in the fertilizer. They are universally nitrogen (N), phosphorus (P), and potassium (K), in that order. These 3 elements do the bulk of the work in feeding your plant and are the standard by which you can compare fertilizers. 

  • Nitrogen stimulates strong stems and healthy, green leaves. While nitrogen is important for all plants, nitrogen heavy ratios are favored by plants grown for their foliage.
  • Phosphorus promotes flowering and fruiting. If you want big blooms, you will want that middle number to be higher than the other two.
  • Potassium is for photosynthesis and healthy root production. It is important not to overlook humble potassium. Healthy roots make for a healthy plant.

NOTE: Hydroponic fertilizers differ from those made for soils as they must be water soluble and contain all the micronutrients a plant needs that would naturally occur in soils.

Soil vs. Grow Media

Soil and grow media perform the same essential jobs of anchoring the plant, supplying nutrients and water, and allowing gas exchange in the roots. Soil refers specifically to the loose outer layer of the Earth’s crust that supports life. A growing media is a manufactured substrate for plant growth.

Think of it as soil is weathered from nature while growing media is manmade. It is important to understand the difference between these two in order to understand how and when to water your plant and what kind of fertilizer to apply.

Examples of soil are topsoil under your yard, sand, silt, clay, and hardpan. Growing media includes coco-fiber, rockwool, clay pebbles, perlite, vermiculite and peat moss. Potting soil is actually a growing media too and rarely contains mineral soil at all.

PRO TIP: You never want to use soil from the ground in your hydroponic system as you never know what pathogens it could contain.


In our earlier post, we talked about the various attributes of grow lights like Watts, lumens, and Kelvin. There is another less well known way of comparing grow lights however and that is Photosynthetically Active Radiation, or PAR. PAR is the amount of light within the visible spectrum (400-700 nanometers) that plants use during photosynthesis. Just like humans measure light intensity in lumens, light intensity for a plant is measured in PAR. PPF, or Photosynthetic Photon Flux, is basically synonymous with PAR as it is simply describing the flow of photons to the leaves of the plant.

However, photons (the fundamental particle of light) carry different amounts of energy at different wavelengths. Chlorophyll within plants cells is most efficient at utilizing light within the blue and red spectrum however, photons within the red range (>600nm) have about half the energy than those in the blue range (<500nm).

PAR meters can be very effective at determining how much light your plant may be getting, but they are simply photon counters and do not show the different energy levels within the light. Hence, a lamp may claim to have an extremely high PAR, but if it is within the red spectrum it will actually not have nearly as much photo-synthetically usable light as one that had the same PAR within the blue spectrum. Therefore, while PAR is good to know, it’s not the end-all-be-all when comparing grow lights

Words to the Wise

Feeling less glassy-eyed? I thought so. Now go impress your friends with your new plant knowledge. And remember that our helpful staff is on hand to help you defog the mystery of hydroponics.

Still stumped? Look for our next installment of hydroponic terms to know or leave a suggestion on FacebookTwitterGoogle PlusLinkedIn, or Pinterest!



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