About Fertilizer Label Numbers

Reading the label on commercial fertilizers can be confusing unless you understand what the numbers mean and when to use them. The three numbers, such as 5-10-10, represent the percentage of nitrogen, phosphorus, and potassium in the fertilizer. Knowing which fertilizer to buy to fit your needs requires an understanding of what each component does and how it will benefit your yard or garden.

Function

Nitrogen is the element that produces lush green vegetation. Applying nitrogen will promote rapid growth and plenty of vegetation, but it will also inhibit blooming and the onset of fruits. Excessive amounts of nitrogen will cause leaves to turn yellow or brown and die.

Phosphorus promotes blooming and the onset of fruit, It also builds strong root systems to sustain the plants in harsh weather and to promote adequate water and nutrients throughout the growing season.

Potassium adds strength to the plant and aids in the production of proteins and carbohydrates. It also helps the plant to regulate growth.

Effects

A well balanced formula provides plants with the necessary nutrients to promote growth and production. When applied at the appropriate time, formulas heavy in a particular nutrient can promote specific actions.

The addition of a high phosphorus fertilizer just prior to blooming will promote large colorful blooms and healthy fruit onset.

A high nitrogen formula will promote lush green foliage, but if applied at blooming time it may inhibit blooming and onset of fruit.

Plants with brown scorched leaves that curl at the end and yellowing veins would benefit from an application of high phosphorus fertilizer.

Risk Factors

Applying fertilizers that are not balanced formulas, or over applying any fertilizer, carries the risk of damaging plants and inhibiting growth. Applying fertilizers heavy in one nutrient needs to be done at the proper time to produce the results you seek. Commercial fertilizers can burn young roots and leaves and depending on your soil type, they can build up in the soil.

Benefits

Commercial fertilizer is readily available and is easy to apply. There are two basic types of fertilizer to choose from: granular formulas that must be mixed into the soil prior to planting, or used to side dress plants during the growing season; and water soluble fertilizers that are mixed with water and applied by a sprayer or from a watering can. They are easy to apply and come in a predetermined formula that does not require mixing or determining percentages of nutrients.

Misconceptions

Many gardeners mistakenly assume that all gardeners should use the same formula to produce similar results. The formula you choose depends upon your soil type and the naturally occurring nutrients in your soil. A good soil test is always advised prior to establishing a new garden bed and should be repeated periodically to determine the PH level and fertilization needs of your soil. Contact your local cooperative extension office to obtain a soil test and recommendations for amending the soil and adjusting PH levels.

Lack of growth or weak plants are your signal to investigate the needs of your particular soil and plants. Providing more of the same fertilizer is unlikely to produce the results you seek, unless of course you have neglected to provide adequate fertilizer in your plant's early stages of growth. It is more likely that your plants require a different combination of nitrogen, phosphorus and potassium or need an adjustment in PH level to enable the plants to absorb the nutrients your current fertilizer supplies.