March 23, 2025 – It’s spring, and it is time to feed your plants! It is highly recommended to have a soil test done BEFORE adding fertilizer to your landscape! Free soil test bags are available at the AgriLife Extension office, and a soil test is only $12.
All containers of fertilizer sold at nurseries and garden centers are labeled with 3 numbers. These numbers show the percentage of the main nutrients in the fertilizer that are available for the plant to use.
First number is NITROGEN. Nitrogen is responsible for the green parts of the plant— green grass for lawns, and green leaves for flowers and vegetables. Since nitrogen is water soluble, the amount available to plants will dissipate after a few rains or waterings, and must be re-applied several times throughout the growing season.
The second number listed is PHOSPHOROUS. Phosphorous is the chemical that promotes root growth, flowering, and fruiting. Unlike nitrogen, phosphorous tends to accumulate in the soil, and should not be over-applied, as a high level of phosphorous locks other nutrients into the soil, making them unavailable to the plant.
The third number is for POTASSIUM. Potassium aids in the overall health of the plant, and increases disease resistance. Potassium helps move and regulate water and nutrients in the plant. Low potassium levels are harmful to your plants in the summer heat, and potassium deficiency is more evident during dry spells.
EXAMPLES **********
A 15-5-10 bag of fertilizer will consist of 15% nitrogen, 5% phosphorous, and 10% potassium. IMHO, this is a good general fertilizer for most gardening/lawn applications.
A 21-0-0 fertilizer is 21% nitrogen, with NO phosphorous or potassium, making it great for green lawns and pasture grasses.
A 13-13-13 blend is an equal balance of all three (NPK). Due to its high phosphorous level, this formulation probably should be used only after a soil test has been done.
For lawns, a fertilizer with 3-1-2 or a 4-1-2 ratio of NPK is a good overall choice. A simple plan for feeding your lawn is monthly applications in April, May, and June, and a fall feeding in September. Feeding in the hot months (July and August) is not recommended, but the gardener should pay close attention to watering during the dry summer months.
For flowering plants, a fertilizer with a higher middle number (phosphorous) will result in more flowers. Vegetable plants (tomato, pepper, squash, beans, peas, and others) will also appreciate a feeding of phosphorous on a regular basis. Miracle Grow makes a variety of excellent high phosphorous flower producing fertilizers, as well as balanced ones. Check the numbers to make sure you are buying what you need. I saw a $20 liquid fertilizer in a nursery last week that was 0-0-.03!! Buyer be informed and beware!!
Weed and feed products are a combination of fertilizer and weed control. Usually these are more expensive, and in most cases, using fertilizer and weed control products separately produce better results. Do not use weed and feed products under or around trees, as some weed control ingredients can be harmful to your valuable trees.
