When to prune depends largely as to why you are pruning. Light corrective pruning and removing dead wood can be done almost any time. Major pruning is best done during the dormant season. Hear are some guidelines. Timing for individual species may differ.
During winter, growth slows and plants gradually become dormant. In mild climates they are semi dormant. Pruning when plants are not actively growing is the most common timing, resulting in vigorous new growth the following spring. Typically, it’s best to prune after the coldest part of winter has passed. Some plants, such as mesquites, ashes, and sycamores, may bleed when the sap begins to flow. This is not harmful and will cease when the tree leafs out.
Prune trees or shrubs that bloom in summer or fall on current year’s growth in winter. Examples are crape myrtle, pomegranates and roses.
Plants that freeze or go dormant during the winter such as Caesalpinia gilliesii, C. pulcherrima and Salvia leucantha should be pruned back in late winter or within 1 to 1/2 feet from the crown or base. In warm-winter areas, Caesalpinia gilliesii and C. pulcherrima may remain green and alive but pruning helps keep plants compact and in control, plus encourages fresh, healthy, new growth.
Late winter is also the time to thin the canopies of young, fast-growing trees such as Prosopis hybrids, mesquites, and many Acacia species. Left unpruned, the dense canopies can catch the strong spring winds, causing trees to blow over.
Plants such as azalea, camellia, Cassia, Cordia boissieri, Calliundra eriophylla, Justicia, Photinial and Sophora species develop flowers on the previous year’s growth. Prune after bloom period is completed. If you find their seed pods unattractive, remove them at this time. To increase side growth for a more compact plant, pinch off vigorous vertical tips.
Prune frost-tender shrubs as they come out of winter dormancy in spring: lantana, bougainvillea, cape honeysuckle, hibiscus, justicia, natal plum and plumbago usually need severe pruning to control growth. If plants are damaged by frost, they may need pruning later in the season, depending on climate and how late in the year frost occurs.
Hardy, nonblooming shrubs grown for their dense foliage can be pruned lightly any time. But pruning cuts heal more quickly if pruning is done right before new growth begins in spring. Heavy pruning should be done in February and March. Examples include juniper, Nandina, Pittusporum tobira and Xylosma.
Prune trees and shrubs that bloom in spring from buds on one-year-old wood. Examples are dogwood and flowering fruit trees. Wait to prune until after their flowers fade.
Direct growth by removing branches you don’t want. Summer pruning can slow or dwarf the development of a tree or branch by reducing the total leaf surface. This reduces the amount of food manufactured and sent to the roots, and slows development of next year’s growth. Don’t prune so much that branches are exposed to intense sun.
Summer is also the time for minor corrective pruning of fast-growing shrubs such as bougainvillea, cape honeysuckle and hibiscus. Dead limbs can be seen more easily, as well as limbs that hang down too far under weight of leaves.
Many shrubs benefit from periodic pinching during the growing season to maintain their shape. Remove spent blooms and seed pods. You may have to sacrifice a few flowers of summer-blooming varieties to keep plants in control.
Decay fungi spread their spores profusely in the fall. Fresh pruning cuts are an invitation, so avoid pruning now. Cuts seem to heal slower when performed at this time. Wait for the winter season to prune.
Trees are the most valuable elements of a landscape, for many reasons. They add structure, form and character. Many add seasonal color and shade. They provide the framework from which to build a balanced, pleasing landscape. Deciduous trees provide shade in summer, then allow the sun to shine through their branches in winter. Evergreen trees are in leaf all year and serve as windbreaks and screens for privacy.
When you plant trees, be aware that they require more care when young and less and less as they mature. Arid land trees have different requirements compared to trees grown in temperate climates with abundant rainfall.
When pruning young trees – those three to four years old – the goal is to establish strong girth or width in a single-trunk tree. The stronger the trunk, the more apt it will be able to grow without stakes. If you are growing a multi-trunk specimen, your goal should be to develop three to four strong leaders.
To develop strong trunks, do not remove lower branches. They “feed the trunk in the area and protect bark from sun damage. Leave these lower branches in place for a few years. They can then be pruned up for a more refined look or to allow for pedestrian traffic beneath. Trim the interior to establish the desired branch spacing. Your goals should be to reduce the potential for wind damage while also increasing penetration of light. Remove branches that are dead, weakened, injured, diseased, or damaged.
Protect the trunks of young trees from high heat and intense sunlight. If trees produce heavy canopy growth, this is often enough to shade the trunk. Unfortunately, most side branches on single-trunk trees grown in containers are removed at the nursery. Low side branches are often left on multi-trunk trees. If trunks require protection from sunburn apply white latex paint diluted by half with water. Commercial tree trunk paints are also available.
To thin young trees as well as mature trees, selectively remove branches. You want to improve structure, control unwieldy branches, “lift up” lower branches by removing them from the trunk and thin the interior to decrease wind resistance. Improving branch spacing also preserves the tree’s natural shape.
Don’t prune too much at one time, especially during the summer in hot climates. Pruning removes leaves, branches, buds and stored energy, all of which benefit the tree and are needed for proper growth. Removing too many branches also increases susceptibility to pests, slows growth, undermines health and stimulates excessive sprouting.
In the West, certain trees such as Brachychiton populneus, bottle tree, tall-growing Eucalyptus species, and Populus species, poplar, are commonly planted where their height and vigorous root systems create serious problems.
In many situations the ultimate height, spread, rate of growth and pruning needs were not matched to the site. In addition, if large trees are not maintained regularly, major problems tend to develop. Aging branches can break and fall.
Information courtesy of ‘Johnson’s Guide for the Arid West’
For more informative answers to questions contact the University of Arizona, Maricopa County, Cooperative Extension Service at (602) 470-8086.