Abundant rainfall spurs tree growth, which may require pruning

After two consecutive years of normal and above-normal rainfall, trees, hedges and bushes whose growth was constrained during the drought years have shown a huge growth spurt this spring. My neighbor's magnificent loropetalum hedge is at least four feet taller and wider. The small ligustrum trees planted alongside my back fence increased twofold in size so that their branches reached into my neighbor's rain gutters; the flower clusters were enormous. The Meyer lemon tree in the center of my small backyard grew so large that the branches completely blocked the pathways.           

It's so nice to have a lush garden again (however short the time until drought resumes) but the vigorous plant growth will cause problems this summer.

Plants and trees that have suddenly outgrown their spaces this spring will obviously need to be trimmed back, but the trimming and pruning should not be a one-time major cut back. Reducing the size of the leaf canopy by more than 25 to 30 percent during the growing season removes too much of the plants' and trees' sources of energy and can cause stunted growth. A light pruning using thinning cuts to reshape the outer canopy of only those branches that are obstructing access or that risk causing property damage would be best during the summer. Leave the removal of larger branches and branch scaffold restructuring until winter when deciduous trees are dormant.

The recent overgrowth on many plants will have shaded the soil underneath the larger canopy as well as the roots that extended to the edge of the enlarged canopy. Those roots may well die back in the hot soil. Expect to see some wilting and signs of heat stress after even moderate pruning.        

The second caution on pruning overgrown plants this summer involves the risk of sunburn on newly exposed interior wood. We can expect that the Central Valley will experience several heat spikes, or long periods of high daytime temperatures (above 100 degrees) along with warm nighttime temperatures, in the next few months. Sunburn is a common problem on hedges that are pruned heavily during the summer in the Central Valley with the hedge tops showing most of the damage from the sun's rays. It's best to shear hedges lightly and frequently, every six to eight weeks, in the summer. To help reduce damage from sunburn, use a mixture of half water/half white latex paint on exposed wood, especially on citrus and other fruit and nut trees, to reflect some of the sun's harsh rays. The open center or vase-shaped pruning system on most fruit and nut trees should be maintained in the summer months.

The UC ANR publication 8057 on pruning deciduous trees has line drawings of several pruning methods and a glossary of pruning terms, which provide very basic pruning information. A long time favorite pruning guide, Orthos' ‘All About Pruning,' is once again out of print but worth searching for in used book stores for its excellent detailed descriptions, drawings and photos of the proper pruning techniques specific to many tree and bush species. DK Publishing (one of the best publishers of garden books) has “Grow Pruning and Training" ISBN 9780744026832, $12.99, which seems to be a good replacement for the Ortho guide.