Apply fertilizer in small quantities

Despite what you see on certain product labels at garden centers, fertilizer is not plant food. Foods are carbon-based substances - primarily carbohydrates, fats and proteins - that organisms can break down to provide energy and the building blocks to construct and repair living tissue.

Green plants make their own food; they don't get it from an outside source. They use energy from the sun to assemble carbohydrates, fats and proteins from simpler components. What plants do need from the outside are these simpler components: water, carbon dioxide (which they obtain from the air) and certain nutrient elements (nitrogen, phosphorus, potassium) that occur naturally in the soil.

A deficiency of one or more of the nutrient elements can limit plant growth and development. So as good gardeners, we add fertilizer to the soil to prevent deficiencies.

The problem with thinking of fertilizer as food is one of scale. Food is something we people need frequently and in large quantities. Fertilizer is something to be applied occasionally and in small quantities - especially if it contains high doses of nutrients. Too much fertilizer can damage plant roots, and heavy rains or watering can wash nutrient elements into ponds and streams where they become pollutants.

Nutrient elements are held in the soil mostly by organic matter and clay particles. Unfortunately, sandy soils in Florida have little of either. But even in our infertile soils, fertilizer is not always necessary. It depends on the situation.

If plants are small and immature or if organic matter (such as fruits, vegetables and clippings) are being regularly removed from the landscape, thus interrupting natural recycling, then the addition of synthetic fertilizer, manure or compost is important.

However, if plants are mature perennials, they need very little, if any, fertilizer. The plant is considered in a state of equilibrium. Its older leaves will die and fall to the ground where they decay, releasing nitrogen, potassium and other elements into the soil. Those nutrients can be taken up by the plant's roots and used in the creation of new leaves. The cycle is complete.

To assess the fertility of the soil in your landscape and to receive fertilizer recommendations for certain lawn and landscape plants, consider having a sample of your soil tested. Collecting a sample is simple and it costs just $10 per sample for analysis at the UF soil testing lab. For details on this service, read the online UF extension publication "Soil sampling and testing for the home landscape or vegetable garden" at edis.ifas.ufl.edu/SS494, or call your local county extension office.