There is no one best type of plant food. Healthy plants need a mixture of chemical and mineral nutrients. The three basic elements that all plants need are nitrogen, phosphorus and potassium. Small amounts of minerals such as calcium, iron, manganese and magnesium are also necessary for healthy plant growth. The ratio of these plant foods needed in the soil varies according to the needs of individual plant types.
The term "plant food" is a bit misleading in that it makes people tend to think that plants need regular feeding just as people do. According to Washington State University, plants make their own food by using the nutrients in the soil and sunlight to make carbohydrate compounds by photosynthesis.
Food for Perennials
Perennials go dormant in winter and come back in the spring. Provide them with extra nutrients to get them off to a good start as they put out new leafy growth.
According to University of Illinois perennials are not heavy feeders. If the soil has adequate organic matter only a small amount of extra nitrogen will be needed. Unless your soil test indicates otherwise, about a pound of a general purpose fertilizer such as 10-10-10 in the early spring will provide them with enough nutrients to start and also store up some for the summer.
The numbers 10-10-10 indicate that the plant food contains 10 percent nitrogen, 10 percent phosphorus and 10 percent soluble potassium.
Food for Acid-Loving Plants
There are some garden plants that prefer an acidic soil. Conifer trees, roses, raspberries, dogwood, camellias and azaleas are all plants that like an acidic soil. Fertilizers made with cottonseed meal are a good choice for these plants because the nitrogen is bound up in organic molecules and is not released until the microorganisms in the soil have broken it down. North Carolina State University recommends applying 2 to 5 lbs. of cottonseed meal fertilizer per thousand feet of garden space.
According to the University of California, many gardeners will feed acid-loving plants a 0-10-10 fertilizer mix in the fall. This supplies the plants with the nutrients most needed during the winter dormant time but won’t promote new growth.