As indicated by soil analysis, throughout the growing cycle. Copper is not readily mobile within the plant, so must be continuously available, although in small amounts. Too much copper in the soil is harmful, so soil analysis testing is necessary.
The availability and sufficiency of copper in the soil is essential to strong, healthy growth and high yields. Copper supports photosynthesis, structural strength, respiration, enzymatic processes, pollen virility, carbohydrate and protein metabolism, as well as the flavour of fruit.