Tamarix is a genus of about 50 species of flowering shrub native to Eurasia and Africa. Some Tamarix species, which have the common name of tamarisk, can be invasive in the U.S. and have become naturalised in parts of the American Southwest. Tamarix species bloom either in the spring or in the fall, and pruning practices must be undertaken based on the season in which the tamarisk blooms. A good pruning can rejuvenate even an old and neglected tamarisk, provided the pruning occurs at the proper time of year.
Determine the season in which your tamarisk blooms. You can consult a nursery, a guide to flowering shrubs or the Web to identify your tamarisk and its season of bloom. Tamarix tentandra, for example, is a spring-flowering tamarisk.
Understand the types of pruning you'll be undertaking. Deciduous shrubs such as the tamarisk should undergo three types of pruning: thinning, gradual renewal pruning and rejuvenation pruning. The first two should be accomplished annually. In the case of an overgrown tamarisk, you first need to do a rejuvenation pruning at the proper time of year.
Rejuvenate your tamarisk at the proper time of year. Prune spring-flowering species just after flowers fade in late spring. Prune fall- or late-summer-flowering species in late winter. To perform rejuvenation pruning, cut back one-third of the oldest and largest branches to ground level.
Thin out the remaining growth at the same time by cutting twigs or stems at the main trunk, a lateral side branch or a "Y"-intersection of branches. This type of pruning further opens up the tamarisk and promotes lateral growth while discouraging the top-heavy growth characteristic of an untended tamarisk.
Repeat your pruning from year to year at the same time of year as the initial rejuvenation. Practice gradual renewal pruning by cutting a few of the oldest and tallest branches to the ground every year and thin out the remaining growth to ensure a long and healthy life for your tamarisk.