Arid plants are not supposed to look like boxes, spheres, pyramids, or aircraft carriers. Pruning to create a novelty topiary like one might find at an amusement park is tedious work requiring lots of time and dedication. It is best left to professionals working with compatible plants such as boxwood or myrtle. These plants must be sheared frequently to maintain those exotic shapes.
Most of the plants that we call arid adaptive flower profusely. The main reason to refrain from shearing them is that many of the flowers are inadvertently pruned off in the process. As a result the bloom potential is greatly reduced. Secondly, these plants have not evolved to maintain large amounts of foliage. Shearing them produces lots of foliage thereby reducing their water efficient nature. This includes Texas Ranger (Leucophyllum), Cassia (Senna), Creosote (Larrea), and many others.
Texas Rangers In Unnatural Shapes
Why do landscape crews shear arid adapted plants? Well, it is mostly because they have been taught to do so by prior landscapers. There was a notion that the more you pruned off and hauled away the better as the property manager could visually see a change in appearance. Those who know better certainly notice all right. It's also very easy to teach others how to do it. Mindless work that fills hours on the time cards that result in large labor cost passed on to the customer.
In the long run the landscape winds up looking like any other heavily trimmed property, with fewer flowers, a large load of foliage going to the landfill, and a water-thirsty collection of shrubs that must now regrow everything that was pruned off. This doesn't sound very eco-friendly does it?
Pruning desert-adapted shrubs to maintain a natural shape and to improve flowering is easy. First, if the shrub has been routinely sheared to create a geometric form then it should be pruned hard to eliminate all the unnatural top growth. Heavy trimming of this type is called rejuvenation pruning. The shrub is simply cut down to within 4 to 6 inches above ground level. The new growth that emerges may be trained to create a more natural shaped shrub.
Timing is critical to succeed with radical procedures such as this. Rejuvenation pruning should be done during the winter for summer flowering plants (Texas rangers, crapemyrtle) and after the bloom cycle for spring flowering plants (Cassia, brittle bush, autumn sage). Once the new growth fills out you may conduct maintenance pruning in one of two methods: the two-step naturalistic or the one-third per year method.
The two-step naturalistic method was created by the late Eric Johnson from Palm Desert. His method called for the trimming of the heaviest stems each year. These are cut back by one third of their length preferably to a point where an inner branch may then take the lead. Once the largest stems are cut in this manner then all the remaining branches are lightly pruned removing several inches of foliage in a variable manner. This does not equate to shearing and the shape should be informal in appearance. Repeat annually at the appropriate time.
The other method is the one-third per year method. This pruning eliminates the heaviest stems all the way down to ground level. New stems will emerge near this cut replacing the older stems. The process is repeated yearly at the appropriate time. By the end of the third year all of the above-ground stems are less than three years old ensuring that all of the new foliage produces bountiful flowers.
Informal pruning practices such as those described will produce a bounty of flowers, sustainable new growth, and a more water efficient plant. In return the maintenance effort is greatly reduced allowing more time for irrigation management and weed control. Let's not forget that less is hauled to the landfill thereby reducing the burden of disposal. An lastly, most of the work can be done without the use of power tools. Imagine a landscape crew that does not have to use hedge shears and blowers powered by gasoline engines. You could actually hear the birds singing while they work! What a novel concept!
Beautifully Shaped Cassia in Full Bloom