Nutrition is one of the cornerstones of growing a healthy garden. Soil needs the proper amount of nutrients for plants to achieve optimum health and beauty. Of the many kinds of fertilizers available, controlled-release plant foods are among the most useful in achieving and maintaining good soil nutrition over time.
A controlled-release plant food, or slow-release fertilizer, is one that makes some nutrients available over time, rather than immediately after application. These plant foods release their nutrients slowly over time because they are made from insoluble ingredients, which do not immediately dissolve in water.
Controlled-release plant foods, releasing their nutrients slowly, feed plants over longer periods as opposed to fast-release plant foods. Application is less frequent than with soluble fertilizers. A slow release of nutrients keeps tender plant roots from becoming burned by high concentrations of chemicals.
Controlled-release plant foods are most commonly available in granular form. These are most often used for flower and vegetable gardens. Granular products are available for lawns, trees and shrubs as well. Slow-release plant spikes are available for large trees and shrubs and dissolve throughout a season, while plant tablets and smaller spikes do the same job with houseplants and smaller garden plants.
A typical release time for controlled-release products is 90 to 120 days. They are properly applied in those intervals. Fertilizing plants at planting is not usually recommended because of potential chemical root burn. Slow-release plant foods, on the other hand, can be applied at planting because they don't cause burning and overfertilization. Use all products according to instructions on the label.
There are many natural products and additives that release nutrients slowly into the soil. Compost and composted manure contain nitrogen that penetrates soil as it breaks down. Bone meal, made from pulverized chicken bones, releases phosphorus and calcium. Greensand releases potassium and several micronutrients over time. Not to be confused with sand, greensand (glauconite) is a natural nutrient product available at garden centers.