Take it easy on hedges in summer months

Hedges grow rapidly during the summer months. Because it’s too hot to spend much time working in the garden in July and August, many gardeners try to cut back their overgrown hedges with one heavy pruning whack job. Removing too much of the new growth at one time exposes the tender interior wood to summer’s hot harsh sun just when it needs shade. The exposed wood then dies back, which is why we see so many brown scraggly, half dead hedges in late summer.

Instead of heavily shearing them, lightly clip hedges (boxwood, ligustrum or privet, myrtle, osmanthus, etc.) every two to three weeks during the hot months. Use a string tied to poles or sticks as a leveling guide for pruning tools. If you’re seeing brown hedge tops or brown areas within the hedge, place market umbrellas or shade cloth to temporarily provide shade until new growth can cover exposed wood.

Lavender and evergreen euonymous (bright yellow daisy-like flowers) are sometimes used as hedges. Both need light pruning in summer to remove flowers but care should be taken to not cut into the woody portions of the plants. Cutting these plants back too far will deform their natural shape. Shear off only the flowers and the stems. Plan on replacing larger species of lavender every few years when the plants become rangy and produce fewer flower spikes. Dwarf varieties of lavender tend to maintain shape for a few more years.

Note: Two readers were concerned about serious fire blight problems with ornamental pear trees this season, including those in Fresno’s Shinzen gardens. We had unusually humid warm weather this spring; high humidity and warm temperatures (between 75 and 85 degrees) favor the proliferation of the bacteria that cause fire blight in members of the pome family (especially apples, pears, pyracantha).

The first symptoms of fire blight appear in spring during active growth. A watery, light tan liquid oozes from cankers or areas of dead bark killed by last year’s infection. New twigs and branch tips are most affected. As the ooze dries on the dead wood it turns black, as do leaves and fruit, making them look scorched, hence the name “fire blight.” Infection by the pathogen can extend into major branches and the trunk and roots, eventually killing susceptible host trees; infected trees will never be entirely free from the disease. Seriously infected trees should be replaced with resistant varieties.

Pruning out infected branches is the most effective control for fire blight, but pruning should be done in summer or winter when the bacteria are no longer spreading. Heavy pruning and fertilization in spring will force new growth that can become infected.

The pathogen extends through the wood in a long narrow path at least two to three feet from a canker. Newly infected woody tissue underneath the bark will show red streaks nearest the oozing source, then reddish flecks further on. Uninfected wood is light brown or tan with no red streaks or flecks.

Use a sharp knife to scrape away bark to determine the extent of the disease’s progress and make pruning cuts at the branch juncture farthest away from the diseased wood. Leave branch collars (the slight ridge where branches join one another or the trunk) intact; they will seal over and help prevent the spread of the disease.

This story was originally published July 28, 2016 at 1:05 AM with the headline "Take it easy on hedges in summer months."