Chaste tree grows quite well in Southern Arizona, though it has its origins in Southern Europe and the Mediterranean. Very shrub-like and naturally multi-trunked, it can be trained to grow as a small tree eventually reaching a mature size of 20 feet tall with a 20 foot spread. The deciduous, aromatic foliage consists of compound, lance-shaped leaves that are a grey-green color above and silvery on the underside. Long, narrow spikes of purple flowers appear in late spring and early summer. The most common flower color is purple. However, certain hybrids have deep blue, white or pink flowers. According to legend, chaste tree was used by medieval monks who found that chewing its leaves helped them maintain their vows of celibacy. This explains the name of this lovely ornamental tree.
Plant chaste tree in the spring, after all danger of frost is past, in full sun or partial shade. Chaste tree does best in well-drained, fertile soil but tolerates drier soils with sufficient irrigation. The first year, water chaste tree every seven to ten days. It can survive on low amounts of water but does best with regular, deep irrigations. Water established chaste trees weekly in the summer and every three to four weeks in winter. To shape into a tree form, prune the lowest branches and any suckers or side shoots each spring, until the crown is as tall as you desire. Prune dead or damaged branches in late spring. By removing the first flush of flowers as soon as they fade, a second bloom can appear in the summer. Chaste tree is not particularly susceptible to pests or diseases.