Coco coir differs from other substrates in many ways, but one big difference is the anion capacity. What does this mean for nitrogen levels in your nutrient solution?

The overall level of nitrogen in your nutrient solution should be based on the plant's need for nitrogen, which is dictated by the amount of photon energy received by the leaves. Higher PPFD levels mean the plant will require more nitrogen. But nitrogen metabolism also requires other elements to complete the nitrogen cycle, such as magnesium, sulfur, and some trace elements. Also, calcium opens up cellular pathways for nitrogen to be used more efficiently by the plant. (Refer to our previous article discussing the importance of calcium in coco coir.)

So we established that the greater the amount of light a plant receives, the more the nitrogen level needs to be increased. Along with nitrogen, the supporting elements should also be increased in the proper ratios to nitrogen. And when these other elements also have interactions with other macroelements such as calcium and phosphorus, we must increase everything proportionately. Meaning, the overall EC of a balanced nutrient solution should be raised when there is a need for more nitrogen.

In general, most coco coir specific nutrients will primarily use calcium nitrate as the source of nitrogen. This is because, as mentioned in a previous article, the coco coir requires some calcium to “charge” the positively charged cation exchange sites. In a similar manner, coco has a high amount of negatively charged anion exchange sites. These sites can hold some nitrogen in reserve, generally 10-20 ppm. However, these anion exchange sites will need to be charged early on in much the same way as the positive cation sites. Therefore, it is recommended to feed about 10-20 ppm more nitrogen early on in coco than in other types of media. This reserve of nitrate is somewhat small, but very mobile and easy for the plant to get to. You may find that it takes a few days longer to get the nitrogen to taper off or “fade” when reducing or eliminating nitrogen before harvest. This is because the plant is not only consuming the stored excess nitrogen in its leaves, but also consuming the reserve of nitrate stored in these exchange sites in the coco itself.

Different grows will have different lighting and environments, so plants will have different nutritional needs. However, as a general guide, we recommend beginning your starts in coco with around 150-190 ppm of nitrogen, and depending on the PPFD, ramping that up to 210-250 as quickly as possible. We also recommend using calcium nitrate as your primary nitrogen source, as this will satisfy both the cation exchange and anion exchange requirement of the coco.