10-10-10 fertilizer is certainly one of the most popular fertilizers. This week, I received a great question about the nutritional difference between it and compost:
Most bags of compost and manure say they have about .1-.1-.1 of the big 3. I have tested my own compost and it is somewhat higher but still not in the 10 10 10 range recommended for most plants. So, how do you get enough without using fertilizers? Is 10-10-10 the same as .1-.1-.1? Am I missing something?
I'm really glad you asked. There are 3 things I'd like to address...
1. Fertilizer Labels
In many countries, in order to be considered a fertilizer, a product must contain a minimum percentage of total nitrogen, available phosphate and soluble potash.
That's often written as NPK - such as 10 10 10 fertilizer or 5-10-5 fertilizer - "the big 3" mentioned in the question above. That required percentage can be quite high, well over 20%.
Notice that it’s available phosphate and soluble potash, not total. This has an unfortunate consequence for organic fertilizers.
Nutrients in organic fertilizers are wrapped up in various organic compounds that need to be broken down by microbes before they become available to plants.
That's how nature does it, and it takes time. Most of these nutrients are not so quickly "available."
That means much of the NPK in these fertilizers doesn't get counted on the label, which means many fertilizers used in organic gardening don't qualify as a fertilizer, and look like poor value when compared to the high numbers of a chemical fertilizer.
They may be sold as soil amendments or perhaps specialty fertilizers, with low NPK numbers.
That's why things like compost and kelp aren't technically "fertilizers." For example, the seaweed I use is only a 0-0-1.
2. What Is A Complete Fertilizer?
Further, the law says a "complete fertilizer" only has to supply these three nutrients. We know, of course, that plants need many dozens of nutrients (perhaps over 70), so it makes no sense to apply only three.
In fact, applying too much of these three indiscriminately often causes more problems than benefits.
As we'll see below, while we need a lot of different nutrients in our soil, we don't need all that much of any of them.
That's one reason why quality compost and biostimulants like sea minerals are often the best garden fertilizer choices - they supply everything in tiny amounts, just to make sure all of the nutrients are covered.
3. How Much Of Each Nutrient Does A Plant Need?
Now, onto your specific questions. 10 10 10 fertilizer is not the same as .1-.1-.1. It contains 100 times more total nitrogen, available phosphate and soluble potash.
And when you mentioned that you're compost doesn't reach the "10-10-10 range recommended for most plants," the fact is that this big range is recommended for the profits of the manufacturers, not for the health of the plants.
You asked how to get enough nutrients without using fertilizers, and the heart of the question is really, "how much of each nutrient does a plant need?"
The answer is shockingly little. Only tiny amounts of each nutrient are actually removed from the soil when we harvest the vegetable garden. We're talking grams of each nutrient.
If our soil is poor and losing nutrients through leaching and volatization, we need to add a little more than if we have a balanced, sustainable ecosystem, but not nearly as much as one might think.
We do still fertilize, but mostly for different reasons (I'll save that for another article).
10-10-10 Fertilizer Summary
The bottom line is:
- Fertilizer labels are very misleading, implying that plants need high amounts of just NPK - plants need many more nutrients than NPK, and they need very small amounts of each.
- The chance that your plants and soil will be happy with 10-10-10 fertilizer is very low - plants prefer their nutrients in organic form, prepared by microbes.
- Well-made compost and biostimulants are some of the best fertilizer choices for supplying what plants really need.
- Sometimes it does make sense to use tiny amounts of N-P-K fertilizer, as I discuss here.
Any questions or comments about 10-10-10 fertilizer? Let me know below.