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Knowing as much as possible about plants makes pruning less confusing

Posted: Sunday, February 07, 2010

There are certain jobs that need to be done in the landscape each year such as fertilization, mulching and pruning. These practices are very important, but can be confusing to gardeners.

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With fertilization, it gets easier if you run a soil sample, because we can tell you what type of fertilizer to use and when to apply it.

With mulching, your plants need a mulch layer 3 to 4 inches deep around them. This mulch needs to be reapplied as it breaks down, and it needs to cover the root system of plants. It doesn't help the plant by piling the mulch around the trunk.

The last and most confusing of these practices is pruning.

Ornamental plants in the home landscape are pruned for many reasons. Some plants are pruned routinely to maintain a desired size or shape. Others are pruned to promote healthy growth, flowering or fruiting. Sometimes it is necessary to prune shrubs that have overgrown their sites, crowd other plants or limit the view from windows. Also, we prune plants that have been damaged by insects, diseases or freezing.

Each plant has its own growth habit and a different requirement for pruning. Some shrubs have dwarf growth habits and might never require pruning, while large shrubs may require frequent pruning.

Improper pruning, or pruning at the wrong time of the year, can result in misshapen plants, reduced flowering or plants that are more likely to be damaged by insects, diseases or winter cold.

When to prune is very important, and there are a few questions to answer before pruning. The first question: Does the plant flower? If the answer is no, then this simplifies when the plant should be pruned.

Plants that don't flower are pruned mainly to shape and reduce the size of the plant. Shrubs that are overgrown and need to be reduced in height can be pruned in late February to early March. Then, light pruning cuts are needed during the summer to shape these plants.

Shrubs shouldn't be pruned in the fall or winter because the plant could put on new growth that can be damaged by cold weather. Some plants, such as boxwoods, junipers, Leyland cypress and pines, don't recover from severe pruning. When too much foliage is removed, it can leave a bare spot.

Plants that flower are pruned according to whether they bloom on new wood or old wood. Plants that bloom on old wood produce blooms in the spring. These plants are azalea, oakleaf hydrangea, crabapple, forsythia and dogwood. There are many more plants that fall into this category.

Plants that bloom on new wood are pruned before new growth begins in the spring. Some of these plants are crape myrtle, rose (except running roses), camellia, beautyberry and sweetshrub. Because camellias bloom in the winter, they should be pruned after they flower, but before new growth begins.

There are two basic types of pruning cuts: heading and thinning. Each results in a different growth response and has specific uses.

Heading removes the terminal portion of shoots or limbs. Heading cuts stimulate regrowth near the cut. It also is the most invigorating type of pruning cut, resulting in thick compact growth and a loss of natural form, as in the case of a formally pruned hedge. Sometimes ornamental shrubs along a foundation overgrow their planting space and are rejuvenated by heading to within 12 inches of ground level. Many broadleaf shrubs, such as burford holly, ligustrum and abelia, tolerate this type of pruning. Other types of heading cuts are topping, dehorning, hedging and clipping.

If the goal is to keep plants in their natural form, then thinning is the pruning method that should be used. A thinning cut removes an entire shoot or limb to its point of origin from the main branch or lateral. Some shoot tips are left undistributed, so apical dominance is maintained. As a result, new growth occurs at the undisturbed shoot tips while lateral bud development and regrowth is suppressed.

Thinning is generally the least invigorating type of pruning cut and provides a more natural growth form of plants. We use thinning cuts to shorten limbs, to improve light penetration into plants and to direct the growth of shoots or limbs.

Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. He can be reached at cphillipshort@comcast.net.



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