Why is it important to know what NPK means? It’s important because chemical fertilizers should not be used indiscriminately. Not all plants have the same nutrient requirements, and you can sometimes do more harm than good when applying chemical fertilizers haphazardly. For example, applying a fertilizer high in nitrogen (indicated by the fact that the first number on the package is high) will cause certain plants to put all their energy into producing foliage, at the expense of flowers.
If you don’t know that much about the nutritional needs of your plant (but still feel the need to feed it at the present time), your best bet is probably to:
· Use compost instead of a chemical fertilizer
· And/or have your soil tested
· And/or stick with a chemical fertilizer labeled as being specifically for that particular type of plant
NPK: The Breakdown
In conclusion, let’s take a brief look at the constituents of NPK:
1. Nitrogen
2. Phosphorus
3. Potassium
Nitrogen promotes leaf development. “Nitrogen” is a major part of chlorophyll and the green color of plants.” As mentioned above, there can be such a thing as “too much nitrogen”; at the opposite end of the spectrum, gardeners sometimes encounter the problem of nitrogen depletion.
Meanwhile, phosphorus plays a key role in the growth of roots, blooming and fruiting. Potassium also plays a part in root growth, as well as in stem development.
You want to make sure your plants are getting the nutrition they need to do you proud, but there are so many choices when it comes to selecting a fertilizer. How do you know what is really in the bag? There are certain rules that all fertilizer makers must follow when they label their products and understanding these rules can make comparing fertilizers much easier.
Here’s How:
1. Major Ingredients: Most commercial fertilizers have 3 numbers on the front label, separated by dashes. For example 5-10-5. This is the fertilizer analysis or percentage by weight of the 3 major nutrients plants need: nitrogen, phosphorus, and potassium, in that order. These are abbreviated as N-P-K.
So if you purchased a 10-pound bag of fertilizer labeled 5-10-5, it would contain 5% nitrogen, 10% phosphorus, and 5% potassium. The remaining 80% could be comprised of other nutrients and filler.
2. 1st Number = Nitrogen: The first number gives the concentration of nitrogen in the product. Nitrogen encourages foliage growth, among other benefits. A 5-10-5 fertilizer would contain 5% nitrogen by weight. So for every pound of fertilizer applied there is really only .05 pounds of nitrogen. (The 10-pound bag mentioned above would contain .5 lb. nitrogen.)
3. 2nd Number = Phosphorous: The middle number refers to the concentration of phosphorous. Phosphorous contributes to many fundamental plant processes such as rooting and setting flower buds. A 5-10-5 fertilizer would contain 10% phosphorous by weight or .1 pounds of phosphorous. (The 10-pound bag mentioned above would contain 1 lb. of phosphorus.)
4. 3rd Number = Potassium: The final number states the concentration of potassium. Potassium contributes to the overall health and vigor of plants. Again, a 5-10-5 fertilizer would contain 5% potassium by weight or .05 pounds of potassium. (The 10-pound bag mentioned above would contain .5 lb. potassium.)
5. Complete Fertilizers: Fertilizers that contain all three major nutrients are considered complete fertilizers. There are specialized fertilizers which are called incomplete because they lack one or more major nutrients such as a fertilizer labeled 0-20-20.
6. Fertilizer Ratio (An easier comparison): An easier way to compare the numbers is to break them down to the fertilizer ratio or the amounts of the 3 major nutrients in relation to each other. A 5-10-5 fertilizer has a ratio of 1-2-1. This becomes important when looking for a fertilizer for a specific need. A 1-2-1 ratio is often recommended for vegetables, which need plenty of phosphorous to set fruit. 1-2-1 could be 5-10-5, 10-20-10 or any similar extrapolation.
7. Other Ingredients: Any additional ingredients will be listed on the side label. This may include other nutrients like calcium, magnesium, iron, micronutrients and even the percentage of organic matter.
8. Organic fertilizers: Organic fertilizers must specify which nutrient(s) is organic and it must be identified as either synthetic and/or natural, by percentage. For example 20% of Nitrogen organic (6% synthetic, 14% organic). When fertilizer is labeled “organic”, it simply means it contains carbon atoms. It can be naturally produced from plant or animal tissue or synthetically manufactured. Until next time…Happy Gardening!!
Jimmie