Tuscan blue (Rosmarinus officinalis) is a fast-growing and upright variety of rosemary, an herb grown for culinary use. Before pruning your Tuscan blue plant, decide on the desired shape. Gardeners typically grow Tuscan blue in the shape of a shrub or a tree. Prune the plant anytime except while it is flowering. Also, avoid heavy pruning in the fall when the expected frost is within 45 days.
Prune your Tuscan blue in the shape of a round shrub by trimming off no more than 1/4 to 1/3 of the plant at any given time. Do not cut back to the main stems, just the top growth. Tuscan blue rosemary will grow even thicker after pruning.
Prune Tuscan blue in shape of a tree by removing the lower branches to the main trunk. Continue to prune off the lower branches as they grow. Trim the top growth in the shape of the tree, but no more than 1/4 to 1/3 of the plant at a time.
Prune diseased or damaged stems at any time of the year. It is usually necessary in the spring.