What you need to know:
Pruning is used to train the plant, maintain plant health, improve the quality of flowers, fruit, foliage, or stems, and sometimes even to restrict growth.
Understanding plant structure helps the home gardener select the limbs or flowers that require removal to improve the health or look of the plant. Resources such as the American Horticultural Society book Principles of Pruning and Training, or Sunset's Western Garden Book, are filled with specific plant life details. Knowing what a bud union is, or a tree crown, or a scaffold branch, or a crotch angle, and the difference between a tree and a shrub, is vital information when a homeowner is ready to begin the pruning process.
The next concern is timing—when to prune. Spring-flowering shrubs and trees that bloom on last season's growth, including azalea, lilac, rhododendron, redbud, Japanese quince, fringe tree, honeysuckle, and viburnum should be pruned soon after they bloom. This allows for vigorous summer growth and plenty of flower buds the following year.
Several years ago, my lilacs were getting tall and sprawly, so I took my loppers to them in the fall in an effort to ‘shape them up'. The following spring, I had tidy lilac shrubs, but very few lilac blooms. I had removed most of the lilac's growth from the previous spring and summer, not knowing lilac is one of the shrubs that bloom on the previous year's growth. Recently, our prolonged cold winter devastated my hydrangeas, resulting in the loss of all last summer's growth. I have very few hydrangea blooms now.
Abelia, butterfly bush, Hills of Snow (a hydrangea variety that does not bloom on the previous year's growth), hypericum, crape myrtle, and most shrub roses bloom after spring from buds which are formed on shoots that grow that same spring. Prune these shrubs in later winter to promote vigorous shoot growth in spring.
Broad-leaved evergreens, such as gardenia, camellia, pyracantha, holly, and photinia require very little pruning. Go several years without pruning, except to remove dead or weak stems, or to keep them neat. Prune broad-leaved evergreens grown for showy fruit such as pyracantha and holly during their dormant season when needed for shaping. If these plants become old and misshapen, cut back to 6 to 8 inches from the ground before spring growth begins. Be mindful of cutting back too early, however, as pruning stimulates new growth, especially vulnerable to frost damage.
Understand the reasons for pruning landscape shrubs and trees, arm yourself with structural and growth knowledge about your specific plant, and be willing to take a hands-on approach to the pruning process You can accomplish the task!
Home gardeners who want to learn more about landscape pruning will find abundant information in the books referenced earlier as well as from these University of California websites:
http://cesutter.ucdavis.edu/files/102457.pdf
http://ceventura.ucanr.edu/Environmental_Horticulture/Landscape/Pruning/
UC Master Gardeners of Napa County is recruiting for the Class of 2015! Applications are available at two information meetings:
Friday July 11, 12.30-2.00
Tuesday July 22, 6-7.30
At 1710 Soscol Ave., Suite 4, Napa, CA 94559.
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. Napa County Master Gardeners ( HYPERLINK "http://ucanr.org/ucmgnapa/" http://ucanr.org/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.
Napa County Master Gardeners welcome the public to visit their demonstration garden at Connolly Ranch on Thursdays, from 10:00 a.m. until noon, except the last Thursday of the month. Connolly Ranch is at 3141 Browns Valley Road at Thompson Avenue in Napa. Enter on Thompson Avenue.