The Best Fertilizer Blend NPK Calculator!

NPK stands for nitrogen, phosphorus, and potassium, which are the three most important macronutrients required by plants to grow and thrive. The numbers that follow the letters NPK on fertilizer bags represent the percentage of each nutrient in the fertilizer, in the order: nitrogen-phosphorus-potassium. For example, a fertilizer labeled 10-10-10 would contain 10% nitrogen, 10% phosphorus and 10% potassium. Technically, in the US, the NPK usually indicates N - P2O5 - K2O. The P and K numbers do not denote pure elemental phosphorus or potassium.

The values for each macronutrient are listed as a percentage of weight. So a ten pound bag of 10-10-10 fertilizer would have a total of one pound each of nitrogen, phosphorus (P2O5) and potassium (K2O). When blending fertilizers you need to know what the weight is of each individual component. This would enable you to calculate the NPK of a custom fertilizer blend.

What's the perfect blend of nutrients? The optimal ratios of NPK can vary depending on the specific needs of different plants and crops. And of course, this will also depend on the soil that you are growing in.

How to Use Fertilizer Blend NPK Calculator:

This fertilizer blend calculator allows you to mix up to five different fertilizer types. Simply input the weight for each fertilizer. It doesn't matter if you're working with ounces or pounds, or if it's grams or kilograms. The only thing that matters is that you need to use the same unit for ALL fertilizers that you are blending. You simply want to supply a ratio.

Next, input the NPK rating, which is stated somewhere on the product label. If you are not mixing all five, simply fill in the fields that apply and leave the others blank. If your fertilizer has zeros, then input those zeros: 34-0-0.

Fertilizer 1:
Fertilizer 2:
Fertilizer 3:
Fertilizer 4:
Fertilizer 5:

You can also use this to calculate the percentages of secondary macros. For example, you can input 2-3-6 to represent calcium (Ca), magnesium (Mg) and sulfur (S).

Many home users will use volume measurements when working with fertilizer products. In case you are interested in a couple basic references, 1 measuring cup of Espoma Garden-tone or Plant-tone fertilizer weighs about 6.6 oz (0.41 lb). Osmocote time release fertilizers have a scoop inside the bag. A single scoop of Osmocote weighs about 1.6 oz (0.24 lb).

Video: Fertilizer Application Rates for Home Gardening
in Containers & Wicking Planters

After years of testing I'm now able to demonstrate fertilizer rates for maintaining optimal plant health.

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