The important elements found in fertilizers
Many chemical fertilizers will also contain trace elements and minor nutrients (minerals such as calcium, iron, magnesium, etc.), all of which are necessary in very small amounts for good plant growth. The label will list the percentages of these microelements as well.
For a bag of fertilizer with an NPK of 10-10-10, the customer knows that 30% of the bag is actual fertilizer, 70% will be fillers or a "carrier." It makes good economic sense to buy the product with the highest total percentage but remember you must know your plants' needs first. If the percentage is higher read the instructions carefully since you may need to apply LESS than the manufacturer recommends!
Since most container plants are placed in potting mixes with little or no nutrients in them, the gardener must provide the necessary fertilizers for good plant growth.