Using the term "plant food" is misleading, because plants produce their own food in their leaves. Various nutrients, extant in fertilizer, are utilized by plants to create tissues and harness the sun's energy to manufacture sugars. Florida in general has sandy, nutrient-poor soils that leach quickly in the heavy thunderstorms each summer. Clay exists in the Panhandle, but addition of organic matter greatly improves the tilth, texture and quality of soils in every part of the Sunshine state.
Contributing writers in "Your Florida Landscape" mention that there are 16 nutrient elements essential to the growth of all garden plants. Nitrogen, phosphorus and potassium are referred to as "macro nutrients" and are utilized in the largest amounts by plants in order to conduct all types of growth and metabolic processes. "Micro" nutrients are needed in minute amounts but play key roles in health of tissues or metabolism. Examples include iron, manganese, copper, boron and magnesium. If native soils lack nutrients necessary for optimal plant growth, gardeners add fertilizers.
Plants cannot differentiate among the various fertilizer formulas or snazzy product names. To a plant, any fertilizer is merely a source of elements. Thus, using an azalea or gardenia fertilizer on other plants still works, as the roots absorb whatever amount or composition of elements are made available. The concern is whether the fertilizer is supplying an ample amount of any nutrient. For example, if a palm is lacking iron and displays yellow fronds, any fertilizer with iron is beneficial. If an insufficient amount is not quickly available, the palm may not fully "green up" after the feeding.
Gerald Kidder and Sydney Park Brown write in "Your Florida Landscape" that you need to fertilize whenever you want a specific plant response the fertilizer product is known to create, such as new green leaves or increased flower production. In general, plants in Florida should not be fertilized in winter when there is any threat of a damaging frost. Always follow product label directions so you apply nutrients at a rate and at a time that doesn't harm the plant.
Both organic and inorganic/synthetic fertilizers are available. Organic fertilizers include soil amendments like compost, bark, needles, leaf mold, well-rotted manure and other degradable natural materials and concentrated products. Inorganic fertilizers are manufactured in a granular or water-soluble form with definitive, exact proportions of nutrients and other components. Granular fertilizers tend to be slow-acting; they slowly release nutrients to plant roots over a season. Water-soluble fertilizers are fast-acting, with nutrients that are immediately absorbed by roots.
Soil pH affects a plant's ability to absorb nutrients in the soil. In peninsular Florida, many sandy soils are neutral to alkaline in pH, resulting in many deficiencies in micronutrients in plants such as palms or evergreen shrubs like gardenia, azalea and camellia. More acidic soils occur in the clay soils in northern counties and are maintained by acid-forming debris like pine needles and bark. Contact your local Cooperative Extension office for guidance on which fertilizers are best in your region, as well as fertilizer formulas best used for different plant types (like citrus, palms, vegetables or lawn grass). Recommended seasonal timing for fertilizing differs slightly in north, central and south Florida locations.