The rate and frequency of application depends on the nutrient analysis of the fertilizer, plant species, soil type, and other factors. For outdoor or garden plants always start with a soil test to determine the amounts of fertilizer needed. There are some general guidelines on how often to fertilize plants.
A granular fertilizer is often applied to vegetable gardens at the beginning of the growing season, usually at planting or prior to planting. Annual flowers may require frequent fertilization throughout the growing season, especially if they are growing in containers. Houseplants need regular fertilization in spring, summer, and fall. Many houseplants do not need fertilizer in the winter. Established perennials may need fertilizer once in the spring every other year. Established trees and shrubs rarely need fertilizer. But these are general recommendations and could vary, so watch your plants. Poor or slow growth and overall yellowing are signs that a plant may be lacking essential plant nutrients and would benefit from an application of fertilizer.