root growth, that part of a vine’s annual growth cycle which takes place below ground. In most fruit trees, the spring flush of root growth occurs at the same time as budbreak, but for the vine it is delayed. There are two peaks of root growth during the year. The first takes place at flowering of the shoots in early summer, and the second coincides with the normal harvest period in autumn. There is an important correlation between the size, health, and activity of the vine’s root system and the growth of shoots and leaves above ground. This is because the roots act as storage sites for the vine’s crucial reserves of carbohydrates and nitrogen compounds, and also as the site for the production of hormones such as cytokinins, gibberellins, and abscisic acid. Vines with restricted or unhealthy roots have low vigour and this is the basis of the principles of balanced pruning. Root growth also varies according to vine age.