Is it necessary to feed plants?
Containerised plants need regular feeding, as they only have what you give them. Plants in beds and borders, by contrast, are able to use the resources present in the garden soil, and may not need feeding.
Ornamental trees and shrubs in garden soil may not need regular feeding by fertiliser. Some crops that do benefit from regular fertiliser are: fruit, vegetables and bedding plants.
Gardeners often assume that poor growth in garden plants is related to lack of soil nutrients and give fertiliser. In fact, results from the RHS Soil Analysis Service show that shortages of plant nutrients in the soil are quite rare. Usually poor growth is due to other environmental factors such as drought, waterlogging and weather damage. Pests and dieases are also responsible for plants making poor growth.
Soils vary in their nutrient levels. Sandy soils and chalky soils tend to be lower in nutrients than clay or loam soils. Soils also vary in the availability of nutrients. Soils that are dry, waterlogged, very acid or very alkaline may not allow plants to access existing nutrients. Correcting these factors (where possible) may be more effective than giving fertiliser, and in fact may be necessary for fertilisers to be effective.
Soil: understanding pH and testing soil
RHS Soil Analysis Service