A fertilizer and plant food buying guide begins with three numbers on the label: N-P-K. They tell you the product's nutrient analysis, not whether it is automatically right for your roses, herbs, or lawn. A soil test and the plant's needs turn those numbers into a useful choice.

Fertilizer N-P-K: what the label measures

The numbers are the percentages of nitrogen, phosphate, and potash expressed under labeling conventions, in that order. A bag marked 10-5-5 has twice the listed nitrogen proportion of either of the other two numbers. The remaining material is not necessarily “empty”; it may include other ingredients or nutrients. “Plant food” is a retail phrase, while plants make sugars through photosynthesis and fertilizer supplies nutrients. Read the guaranteed analysis for details beyond the front of the bag.

Why a higher number is not a better answer

Two products can have the same ratio but different concentrations: 10-5-5 and 20-10-10 have the same relative pattern, yet the latter supplies more nutrients for the same weight. That changes the application amount, not the soil's underlying need. Applying extra phosphorus because a package says “bloom” can waste money when the soil already has enough. Use a recent soil test where practical, follow crop-specific guidance, and avoid guessing from leaf color alone.

Match the form to how you garden

Granular products are measured into soil or scattered as directed, while liquid concentrates must be diluted according to the label. Compare with for the way you actually water and measure. Note coverage per container, frequency, storage instructions, and whether the label names your crop or use. A small pot on a porch has different handling needs from a long vegetable row.

Make the number practical with one calculation

Suppose a label says 10% nitrogen. One pound of product contains one tenth of a pound of nitrogen by weight; that does not mean one pound should be applied to every plant. Read the labeled rate for your planting area and use a measuring container rather than a casual handful. Keep granules away from hard surfaces where runoff can carry them into drains, and store products away from children and pets. If your soil report shows no need for phosphorus, seek an analysis with little or none instead of blindly choosing a balanced blend.

Label-reading checklist

• Identify the crop and consult a soil test before selecting the N-P-K ratio.
• Compare concentration and the label's application rate, not just the largest number.
• Check form, coverage, dilution or spreading directions, and storage requirements.
• Apply only as directed and keep fertilizer off pavement and out of waterways.