1.What is NPK?
An npk fertilizer is usually thought of as a chemical fertilizer, but npk applies to any soil amendment that supplies Nitrogen, Phosphorous, and K, Potassium, including organic fertilizers.
The numbers are always in the same order, and refer to the percentage of each element in the fertilizer.
Plants need nitrogen for leaf growth, phosphorus for root formation, stem growth, and fruiting, and potassium for flowering and plant immunity.
An organic npk fertilizer can be slow-releasing or fast-releasing. Many have both quick-releasing “labile” nutrients, and more “recalcitrant” nutrients that break down slowly and supply a steady stream of nutrients over a longer period.
Many organic npk fertilizers need soil organisms to break them down and release their nutrients, so they release more quickly when the soil is warm and the soil food web is at its most active. This is also when you get the most rapid plant growth, and your vegetables really need it.
If you’re growing cool-season vegetables, choose an organic npk fertilizer that breaks down under cooler soil temperatures. See Organic NPK Fertilizers for Cool-Season Vegetables.
Balanced Organic NPK Fertilizers
A “balanced” organic npk fertilizer is one that provides nitrogen, phosphorus, and potassium—the main macronutrients needed by plants.
If you’re looking for a balanced organic npk fertilizer, your choices are generally plant-based, manure-based, or blended. Plant-based npk fertilizers include alfalfa meal, soy meal, and cottonseed meal. Note: Use only cottonseed meal from organic cotton. Conventionally grown cotton has some of the highest pesticide application rates in the country, and usually contains pesticide residues.
Worm Castings are probably the best single-constituent organic balanced npk fertilizer. They provide quick-release nutrients for early growth, as well as slower-releasing nutrients to sustain growth through the season. They also provide beneficial bacteria and fungi to help your plants assimilate these nutrients.
Alfalfa Meal is a close second. It’s a balanced npk fertilizer that provides a steady release of nitrogen, phosphorus, potassium, and some sulfur throughout the growing season, with most of it available during peak growth, when crops need it most. It’s also widely available, relatively cheap, light enough to use in container gardens, and doesn’t attract animals.
NPK stands for "nitrogen, phosphorus, and potassium," the three nutrients that compose complete fertilizers (see below). You will encounter the letters, NPK (sometimes separated by hyphens) when reading the contents ("analysis"; see picture) printed on bags of fertilizer. The description of the fertilizer may not expressly say "NPK" (it may simply be implied), but you will at least see a series of three numbers, which correspond, respectively, to the nitrogen content, phosphorus content and potassium content of that fertilizer.
Also implied is a percentage symbol after each number, because each of the three numbers represents the percentage of that nutrient in the makeup of the fertilizer. Here is an example of how it is used in a sentence: "When I asked at the nursery what the 10-10-10 on the back of the fertilizer bag meant, they said it was the NPK number" (some call it NPK "value" or "ratio").
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