Digging In - Pruning Mugo Pines and Getting Rid of Wiregrass

By Scott Aker
Special to The Washington Post
Thursday, December 11, 2008

Q Our church garden has three mugo pines, seven years old, located next to a stone path. We want to keep them at their current height and width. Can that be achieved, and when should we prune?

A You can maintain the pines with annual pruning. This is done each spring, when new growth is produced.

Look at the tip of every branch and you will see a central bud surrounded by as many as five smaller buds. In spring, all of these buds will begin to elongate. When they do, remove all but two buds on each branch. If you are dealing with a vigorous branch, cut the central bud and leave two side buds. If you are dealing with a weaker branch, leave the central bud and one side bud intact.

You can further contain the pines a few weeks later through a process called "candling." Every remaining bud that elongates more than two inches should be cut back to about a half-inch. This will force the bud to branch and produce compact growth.

These measures will result by the next year in a compact canopy of needles. To provide light and air circulation to the plant, you should thin the major branches, cutting them back to a main branch. You can reduce the overall size of the plant by cutting out the longest, tallest branches. Do this gradually and never remove more than 10 percent of the plant's branches per year.

Our lawn is being taken over by wiregrass. In the fall last year, we killed patches of it but were unable to seed the areas at the time. In the spring, the wiregrass returned with a vengeance. How do we defeat this tenacious weed?

You have two options for controlling wiregrass, known by the more benign name of Bermuda grass in the turf industry.

Bayer Advanced has a selective herbicide that kills Bermuda grass without harming the turf types used in our region. Bermuda grass is persistent, and you may have to make monthly treatments over two growing seasons to eliminate it.

You might instead apply a non-selective herbicide to kill the entire lawn and start over, especially if your lawn is by now mostly full of Bermuda grass and other weeds, or if your soil is poor.

Spray with glyphosate in June, when the Bermuda grass is in active growth. You may need to repeat the application at monthly intervals to finish the job. By fall, you will have a clean slate, and you can add decayed organic matter, lime and slow-release fertilizer to the soil, and till it into the top four to six inches. You can then sow the area with tall fescue and not have to worry about invading Bermuda grass.

Scott Aker is a horticulturist at the U.S. National Arboretum.

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