WTF is NPK?
Fertilizing can be so confusing. What kind to use? How much? How often?!?!
Don’t worry - you’re not alone. In fact, a lot of professionals make mistakes.
When you look at a bag of fertilizer, there’s usually three numbers (sometimes four) printed on the bag. It looks like this:
16 - 4 - 12
What those numbers mean is there’s 16% Nitrogen (N), 4% Phosphorous (P), and 12% Potassium (K). Combined, you would say the NPK is 16-4-12. If there’s a fourth number, it’s usually a percentage of Calcium (Ca) that is also included. These three (or four) minerals are considered the most important macronutrients to plant health. Micronutrients are also super important because of a very complex web of interactions with the way plants uptake minerals. Think about how milk is always “fortified with Vitamin D.” Ever wonder why? It’s because most people don’t get enough vitamin D in their daily nutrition, but it helps to promote the absorption of calcium. Similarly, phosphorous (in perfect quantity) enables trees to uptake other minerals. But if there’s not enough phosphorous - or too much - it actually blocks a tree from utilizing available nutrients.
So… how do you appropriately fertilize?
Here are the questions that need answering:
How many of these important macro- and micro-nutrients are already available?
Is the quantity sufficient, deficient, or in excess?
What are the requirements of the specific tree or plant? (Bananas need a lot more potassium than most other fruit-bearing vegetation, for example)
Once you have the answers to those questions, you can choose an appropriate fertilizer, and apply it responsibly and effectively.
The best way to answer those questions is to get a soil analysis with a comprehensive (and comprehensible) soil analysis. A basic soil analysis should tell you the pH value, the NPK available, and the gross composition of the soil.
If you are lucky enough to live on the Big Island of Hawai’i, with me, I can do this for you and together we can formulate a personalized fertilization prescription for each of your treasured trees - just shoot me an email to get started. If you don’t live nearby, there are online resources available (A great source is the University of Connecticut Soil Nutrient Analysis Laboratory). Beware when sending soil to other states, as counties in many states have either Fire Ant or Golden Nematode QUARANTINES!
If you live in a quarantine area, your soil samples will be destroyed without testing - and there’s usually a disposal fee, so be careful!!
The USDA APHIS website has information regarding which US counties are quarantined. To determine if you are in a fire ant quarantine area, CLICK HERE. To determine if you are in a golden nematode quarantine area (New York State only), CLICK HERE.
