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Archive for Thursday, April 23, 2009

Trimming evergreens without killing them calls for caution

April 23, 2009

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You don’t have to look far to find homes whose entrances, windows and very walls are being gobbled up by yews and junipers planted along the foundations.

Nothing wrong with evergreens planted near house walls — the plants do soften that transition between the wall and the ground. But when a few years of neglect turns these plants into ominous, billowing masses of greenery, it’s time to take out the pruning tools.

Unless your goal is to kill the plants — cutting stems to the ground, grubbing out roots, and replanting — you have to be careful about how much and where you cut evergreens. These plants vary in their tolerance to severe pruning, and the right cut can spell the difference between a plant that is butchered, even dead, and one that is pleasing to look at.

Discerning differences

Take a look at conifers, that group of evergreens with needle-like leaves. You will notice two kinds of branching patterns. Junipers and yews are examples of conifers that branch randomly. Contrast that with pines and spruces, whose branches are arranged in whorls at discrete intervals along their trunks and stems.

Generally, random branching conifers are more tolerant of being wantonly hacked back than are whorled branching conifers. That’s because random branching conifers grow in spurts throughout the growing season, and along their stems have many latent buds just waiting to be awakened when the stem is cut back. Cut back yew when and where you want, and new sprouts will grow out along whatever stubs remain. The same can be said for hemlock, firs, arborvitae and most junipers.

Whorled branching conifers generally have few latent buds on leafless parts of stems, so do not grow again when cut back severely. And, as growth begins, each bud is already programmed for the single flush of growth it will make for that season. Therefore, don’t expect a whorled branching conifer to grow again from where you cut it back to old wood.

Broadleaf evergreens

Not all evergreens have needle-like leaves; so-called broadleaf evergreens, which include plants such as rhododendron, mountain laurel, Oregon grape holly and pieris, have wide leaves.

These plants generally will send up vigorous new growth whether a stem or even the whole plant is cut back severely. There are exceptions, though, such as rhododendrons having smooth bark.

Pruning strategies

The quickest way to bring down the size of any evergreen that resprouts readily is to merely lop the whole plant to near ground level. It will look forlorn for two, perhaps three years as it fills in. Fueled by the large, existing roots system, however, new growth will be rapid.

Another approach to making an overgrown evergreen smaller is to lower it gradually. That takes a little longer, but avoids that two or three years of desolate appearance.

Gradual lowering is also the method of choice if a plant is particularly valuable and you have any doubts about its ability to resprout after severe pruning.

To gradually reduce the size of an overgrown evergreen, each year for a few years cut a few larger limbs back to their origins or to side branches within the canopy. This removes a lot of wood with just a few cuts, and pruning stubs are hidden in the plant canopy rather than staring out from the edge.

Occasional removal of a few large limbs is also a good way to bring down the size of an overgrown whorled branching conifer. Even without regrowth, pruning stubs are at least hidden, and if you choose your cuts carefully, your plant can retain a pleasing form.

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