Slow Release Fertilizers | NPK Fertilizers Series Part 1
Have you ever stood in the home & garden aisle only to be faced with a mega load of fertilizers? Did you think NPK was some hot tech stock? Do I really need this stuff to get big tomatoes or survive on a homestead?
Let's sort through the different choices to help you use slow-release fertilizer like a boss and just get back to the basics in your garden (or "garden" if you could imagine a Boston accent).
We are going to discuss NPK Fertilizers and dig deeper into the slow-release fertilizers or insoluble fertilizers.
Part 2 of this series can be here.
Slow Release Fertilizer - What's the deal yo!!
Slow-release fertilizer is simply another way of describing food for plants that take a much longer time to break down in the soil.
This is in essence what you want for the long term goal of building healthy soil for your garden, or allotment (for all those on the other side of the pond).
This fertilizer or food is not readily available for your plant but is slowly released in the soil over an extended period of time. The best sources of slow-release fertilizers tend to be organic fertilizers such as compost that is rich & dense in hummus.
How does one go about knowing where to get them? Let's first explore what NPK fertilizers mean.
NPK Fertilizer- What does NPK mean?
NPK Fertilizers is the term that is used to describe the different components in fertilizers. You will see the numbers displayed is a set of 3s such 11-10-5. The first number is N, the second number is P, and the third number represents K.
Stick with me here, this will all make sense as you read on.
A Fertilizer example would be NPK of 13-10-5
- N -stands for nitrogen and is represented by the number of 13 in the fertilizer example above
- P -stands for phosphate and is represented by the number 10 in the fertilizer example above
- K- stands for potassium and is represented by the number 5 in the fertilizer example above

Kudos to you for following all this. You'll be the expert when you see a clueless person standing next to you in the garden aisle next time.
Slow Release Fertilizer Examples
You can simply break down the different sources of a slow-release or insoluble fertilizers into 2 main groups. The first group is the more natural materials that are derived from organic materials without refinement.
The second group can also be those made from a refinement process. This groups can be inorganic or organic. Let's see how you can distinguish them.
- Some of the examples of this would be cow manure (which is rich in N or nitrogen), leaves & other plant materials.
- Eggshells, fruit peels, vegetable scraps are all other good examples. These materials will take some time to break down in the soil.
- A simple way to get use these materials is to start a compost pile. You can also start a worm compost bin. There is a video that we put together to show you a simple way to build a worm compost bin. You can click here if you want to see it.
- You may also want to check out a previous post here that shows you a live look in on the bin here.

Frequently Asked Questions
What does NPK mean on fertilizer?
The three numbers are the percentages of nitrogen (N), phosphorus (P), and potassium (K). Nitrogen feeds leaves, phosphorus roots and flowers, and potassium overall health.
What is slow-release fertilizer?
Fertilizer that releases nutrients gradually over weeks or months, so plants get a steady supply and you feed less often. It also reduces the risk of burning roots.
Is slow-release fertilizer better?
For steady, low-maintenance feeding, yes. It avoids the spikes and runoff of quick-release types, though fast feeds are useful when a plant needs an immediate boost.

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