How to Choose the Right Fertilizer
The NPK numbers on fertilizer are a way to provide the nutrients that may be missing in your garden soil, which is why the soil test is important as a first step. Your soil may have plenty of one and not enough of the others. If you get your soil tested by an extension service, you’ll know which numbers to look for when you buy fertilizer.
Many soils have sufficient phosphorus and potassium for plants, but not enough nitrogen. And plants do not use as much phosphorus as nitrogen and potassium. That means that choosing the right fertilizer may mean picking a fertilizer with a higher first number or three different numbers like 16-8-2.
Knowing the NPK values of a fertilizer will help you select one that’s appropriate for the type of plant you’re growing. For example, if you’re growing leafy vegetables, you may want to apply a fertilizer that has a higher nitrogen number to encourage leafy growth. If you’re growing flowers, you may want to apply a fertilizer that has a higher phosphorus number to encourage more blooms.
How to Calculate for NPK Fertilizer
The next step is to measure your garden and calculate the square footage using the formula length times width. Then purchase enough soil for the area.
The fertilizer numbers can be used to calculate how much of a fertilizer needs to be applied to equal 1 pound (0.45 kg) of the nutrient you are trying to add to the soil. So, if the numbers on the fertilizer are 10-10-10, you can divide 100 by 10 and this will tell you that you need 10 pounds (4.5 kg.) of the fertilizer to add 1 pound (0.45 kg) of the nutrient to the soil. If the fertilizer numbers were 20-20-20, you divide 100 by 20 and you know that it will take 5 pounds (2.2 kg) of the fertilizer to add 1 pound (0.45 kg) of the nutrient to the soil.
Applying Fertilizer
Always apply fertilizer according to directions. It’s important to use the recommended rates or even less. Using too much fertilizer is never a good idea and can burn your plants. If you are a pet parent, have a discussion with your garden center representatives to be sure the fertilizers you choose are pet-friendly.