If you’re new to learning about earthworm castings, you might be interested in figuring out what the NPK ratio is. If you don’t know what the NPK ratio is, that stands for Nitrogen, Phosphorus, and Potassium. These are the industry standard statistics on all fertilizers and soil supplements. By the way, if you are don't understand if all worm castings are the same, read our detailed answer here.
The short answer is that it can vary a little bit. Typically the nitrogen is around 1-2 and the phosphorus and potassium are 0. With that said, you’re not getting even close to the full story about what’s in worm castings by looking at the NPK ratio.
So if the NPK of worm castings isn’t that important to compare, what should you be looking at?
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It’s All About the Microbes
You thought it was all about the Benjamins? No…it’s all about the microbes. At least when you’re talking about worm castings and plant growth. Premium worm castings like Simple Grow have thousands of beneficial microbes in them that come from the worm’s digestive tract. These microbes lead to massive plant growth and make plants grow faster also.
One of the big reasons that this happens is because the microbes break down the available nutrients for the plant. This gets them into an easily digestible format for the plants.
By comparison, if you pick up a synthetic fertilizer off the shelf with 15 percent nitrogen, the plant might only be able to use 1 percent of that. That’s because a lot of the nitrogen, phosphorus and potassium in many fertilizers is essentially unusable for plants. They can’t digest it. So even though that number looks really cool on the side of the package… it’s basically a lie.
With premium worm castings, the microbes make a much bigger difference than nitrogen or potassium or phosphorus could ever dream of making for plants. In addition to the microbes, the worm castings have many trace elements in them that other fertilizers don’t have.
Benefits in the Soil
Besides the microbes and other good things in the worm castings, they also provide the plant additional benefits that pay big dividends. When you mix the castings in with the soil, it provides the benefit of aeration also.
The physical structure of the castings are such that they look like tiny little pellets. They won’t pack down when you put pressure on them, like regular dirt. So they help keep the soil loose, which allows oxygen to the roots of the plant.
Additionally, worm castings help regulate the moisture going to the roots of the plant. When you water, they can actually absorb the water. Then they release the water as the plants need it. It’s like having tiny little sponges mixed in with the soil down by the roots.
Overall, the NPK ratio is basically useless when it comes to worm castings. Yes they do have some nitrogen in them, which helps, but that doesn’t tell you much. You have to throw out the rulebook and look at the big picture. These things help plants grow fast and big, regardless of the stats.