10-10-10 fertilizer is one of the most popular fertilizers.
This week, I received a great question about the nutritional difference between 10-10-10 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 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.
They’re written on the label as 10-10-10 fertilizer or 5-10-5 fertilizer or whatever.
But the percentage that’s required in order to be labeled a fertilizer can be quite high, in some cases over 20%.
Notice that it’s available phosphate and soluble potash, not total.
This has an unfortunate consequence for organic fertilizers because 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, but it takes time, so 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.
They look like poor value when compared to the high numbers of chemical fertilizers, even if the organics will supply more nutrition over time.
With the low NPK numbers, they end up being sold as soil amendments or perhaps specialty fertilizers.
That’s why things like compost and kelp aren’t technically “fertilizers.” For example, the seaweed fertilizer 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 17 nutrients (and probably benefit from many more than that), so it makes no sense to apply only three.
In fact, applying too much of these three indiscriminately often causes problems.
That’s one reason why quality compost and biostimulants like sea minerals are often the best garden fertilizer choices – they supply everything in small amounts, which ensures all of the nutrients are covered.
3. How Much Of Each Nutrient Does A Plant Need?
Now, onto your specific questions.
No, 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 your compost doesn’t reach the 10-10-10 range recommended for most plants, the truth is that range isn’t really recommended for any plant – it’s just something fertilizer manufacturers came up with.
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 volatilization, we need to add a little more than if we have a balanced, sustainable ecosystem, but not nearly as much as one might think.
10-10-10 Fertilizer Summary
The bottom line is:
- Fertilizer labels are 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 low.
- Well-made compost and biostimulants are some of the best fertilizer choices for supplying what plants really need.
- If you want to know how to fertilize properly, this article goes into more detail.
Any questions or comments about 10-10-10 fertilizer? Let me know below.