Southern Homes & Gardens Blog

7-5-4, 20-9-20, 15-7-3. What do all these numbers mean? Whether you use conventional fertilizers or organic fertilizers you’ve probably come across these three numbers listed on the packaging. They are not combinations to a safe, but they can be the key to selecting the appropriate fertilizer for your plants needs.

The first number is the amount of Nitrogen or “N” in the fertilizer. Nitrogen gas comprises about 78% of the earth’s atmosphere. Growing plants, animals and microbial populations need a continual source of N. It is an essential component of the proteins that build cell material and plant tissue. N is often the most important determinant of plant growth. Plants lacking in N will often have stunted growth or yellowish leaves. Just as too little N can be harmful, applying more N than the plant can use can build up in the soil and drain off into our water sources. So make sure that you are using fertilizers with the appropriate amount of N during the appropriate time of year and on the appropriate plants.

The second number is the amount of Phosphorus or “P” in the fertilizer. Like N, Phosphorus participates in the development of new growth and is most critical in root development and seed production. Compounds of P are critical for the plant’s respiration, efficient functioning, and utilization of N. Therefore the symptoms of P deficiency are identical or similar to those which result from a deficiency of N.

The third and final number is the amount of Potassium or “K” in the fertilizer. K assists in the processes that ensure carbon assimilation and the transport of photosynthates through the plant for storage of sugars and proteins. It also assists in the all around growth of the plant. Potassium is important for water regulation and intake. Sufficient potassium helps plants resist frost, drought and certain diseases.

In general, the role of phosphorus and potassium in the plant is maintenance. Both are highly concentrated in new growth and are responsible for keeping the plant system operating smoothly.

By watching your Ns, Ps and Ks, and selecting the appropriate fertilizer, you can help the overall health of your plants and the look of your landscape.

Chris Holley, Garden Center Manager