These three numbers form what is called the fertilizer's N-P-K ratio — the proportion of three plant nutrients in order: nitrogen (N), phosphorus (P) and potassium (K). The product's N-P-K numbers reflect each nutrient's percentage by weight. For example, the label on a 12-pound bag of Pennington Ultragreen Lawn Fertilizer 30-0-4 reveals that
The three NPK numbers on a fertilizer’s label represent the percentage of each element, by weight, inside the package. A package of 24-0-6 fertilizer, in other words, contains 24 percentThe “ideal” soil pH is close to neutral, and neutral soils are considered to fall within a range from a slightly acidic pH of 6.5 to slightly alkaline pH of 7.5. It has been determined that most plant nutrients are optimally available to plants within this 6.5 to 7.5 pH range, plus this range of pH is generally very compatible to plant root
So a 5-5-5 NPK ratio is equal parts of each nutrient and 85% water. This is the NPK ratio that is ideal for tomato seedlings. As plants are maturing and pre-flowering, sticking with a low ratio, around 5-5-5, is still ideal so as not to overwhelm the plant with too many macronutrients in early growth. .