Summer solstice and the growing season

By Bill Pramuk
Trees and People

Here we are, already, at the longest day of the year. The spring rush of growth in trees and the garden has subsided. The first flush of roses has faded and the first flush of growth is maturing in the trees. Little apples are scattered on the ground under my tree — the annual event known as “June drop” when fruit trees naturally adjust the load they are able to carry.

Trees and woody plants generated the spring-flush using food stored in roots and stems last year. They spent it freely while growing conditions were good in spring — moist and warming soil, increasing air temperatures, and increasing daylight.

Now, at the summer solstice, the symphony of trees and environment begins a slower and quieter second movement. The rapid new growth, which exhausted the stored energy in trees and other woody plants, begins to mature. New leaves settle into the quiet, slow and steady work of synthesizing carbohydrates for the tree and the fruit we will harvest.

Faded rose blossoms and June-dropped fruit serve as a reminder that the time is right for summer pruning and cleanup. At this time every year, I need to spend at least one solid day in the garden, weeding, dead-heading the roses and spring-blooming perennials and doing a light pruning for the apple tree.

The concept applies equally to large shade trees.

In a funny twist from my usual expectations, a client called me earlier this spring asking about his oak trees. “Bill,” he said, “why do the oaks look so lush and beautiful this spring?”

He is not the only person to mention this. It does seem that spring was very productive in local trees. Looking first to the most obvious probable causes, it was a result of ample stored energy and good growing conditions in spring. Perhaps that early warm spell helped. Taking a quick look at literature on increasing atmospheric carbon dioxide, which can have a dramatic effect on plant growth, I found that we are far from the level that would trigger noticeable increases in plant growth.

Coinciding with the increasing weight of spring growth, fruit and cones, there have been a number of tree failures: limbs and whole trees giving out under weight and windsail generated in spring.

Another aspect of the second movement of the growing season is a resting period for some of the diseases that affect trees. Many bacterial and fungal diseases of trees require lingering moisture, along with mild temperatures. They also take advantage of fresh wounds as entry courts for infection. When our Mediterranean-type dry summer kicks in, these plant diseases go into a resting phase. Summer is a great time for pruning with respect to tree and disease phenology — biological and seasonal timing.

For trees that we want to maintain smaller than their full natural size, summer pruning has another benefit: a mildly dwarfing effect. Since new growth is only beginning to generate new food for the tree in early summer, pruning at this time removes some of the little food factories — the leaves — resulting in less overall growth.

So, here are a few suggestions for timely tree and garden care in summer:

• Look closely at larger trees for signs of heavy foliage masses, fruit or cones. The canopy of a limb with excessive weight sometimes will separate from the canopy of the tree. The gap of open sky between the two is a visual clue that the limb may be nearing the point of failure.

• Look closely at the attachment point of large limbs and multiple trunks. A deep crease, or worse, an open crack, may be a sign of serious trouble.

• Look closely at the base of the trunk and the soil for signs of movement or instability.

• Examine shade and fruit trees for dead and dying branches, which are often a result of bacterial or fungal infections. Prune out dead and diseased tissue as much as possible while the weather is dry.

 • Conversely, avoid pruning elms and Monterey pines in summer. Dutch Elm disease is carried by bark beetles, which are attracted to wounded and stressed elms. Likewise, pine bark beetles are attracted to wounded and stressed pines, particularly, older Monterey pines in the Napa area. If these must be pruned in summer, consider having them sprayed with a protective insecticide.

• Pick up and remove fallen fruit. June-drop usually includes apples that are infested with codling moths. Larvae in the fallen fruit will show up as the next generation of moths later in the summer or next year.

 • Thin out crowded fruit and lightly prune fruit trees to maintain the desired shape and size. Be sure to retain plenty of foliage to shade and feed the fruit. Foliage also shades and protects stems and trunks from summer sun injury.

Bill Pramuk is a registered consulting arborist. Visit his Web site, www.billpramuk.com, e-mail questions to info@billpramuk.com or call him at 226-2884.

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