Why prune shrubs anyway?

To prune or not to prune, that is the question.
Especially now, as cool weather sets in, people want to know if this is the right time to prune their plants. Fertilizing, watering and weeding are suddenly not so important, as most plants stop growing this time of year.
But if you are blessed or cursed with the endless energy of a gardener, you’ve got to keep busy.
It is generally wisest to prune during the cooler months because during warmer times, when sap is flowing, pruning cuts become entry points for insect pests and debilitating fungi.
The other day I told a student to prune a xylosma shrub; five minutes later, all that remained was a 4-inch stump. Obviously, I had failed to properly communicate what pruning is all about.
Xylosma produces a uniquely curving trunk that should be shown off in a correctly pruned plant. Luckily, the plant in question is one that has the capacity for regrowth. Large, vigorous, woody shrubs – oleander, cotoneaster, privet, pittosporum, viburnum and xylosma – seem to grow back no matter how hard they are pruned.
Many plants, however, do not survive such radical pruning. Among the more pruning-sensitive species are recently introduced flowering shrubs and subshrubs from South Africa and Australia, as well as many California natives. Many of these Mediterranean climate plants are promoted for their drought tolerance and long bloom period; their relatively short life span, compared to the old standby shrubs, is less known.
The stems of most brilliant flowering, dry-climate shrubs are seldom more than half an inch in diameter. This means pruning should be conservative and continuous. Whenever a flowering shoot has stopped blooming, it should be selectively pruned back to a node – the growing point where leaf meets stem. Severe pruning of all stems at once can kill the plant, especially if it’s been in the ground more than five years.
Examples of such pruning-sensitive species include many of the salvias (sages), leucophyllums (Texas rangers) and teucriums (germanders), as well as lavender, rosemary and virtually all other perennial herbs.
The presence of insect pests is one good reason to prune shrubs. In older gardens steeped in the shade of tall trees, mealy bugs and scales are frequently found on the lower portions of shrubs. Cold weather will stop mealy
bugs and scales temporarily, but unless light and air circulation are improved through pruning of overhead trees and the shrubs themselves, these same insects will come back with a vengeance the following spring.
New plantings on the south-facing Ventura Freeway (101) embankments at Balboa Boulevard include several specimens of Salvia Greggii, the autumn sage. In one season, this plant has shown spectacular growth and has nearly reached its mature height of 4 feet. At this very moment, it is covered with red flowers. If this plant is not selectively pruned, and just left alone, it will soon stop flowering and will show little color for many months. To keep it in bloom, shoots with faded flowers would have to be cut back by two-thirds.
It is worth noting that in a 350-page volume titled “The Big Book of Gardening Skills” (Garden Way Publishing, 1993) barely five paragraphs are devoted to the subject of pruning shrubs.
“All shrubs need a certain amount of pruning,” it is written, “if only to remove the dead or damaged branches. Cut off the dead wood as close to the stem as possible. Next, cut the branches that are broken and take off any branch that rubs on another or crosses over it in any way.” This, in a nutshell, is what pruning shrubs is all about.
In order to accomplish this task, you will need three tools: an ordinary hand-held pruning shears ($10 to $20), a long-handled loppers ($30 to $50) and a small folding pruning saw ($10 to $20). You can buy these tools at prices lower than those given above, but inexpensive tools are often of poor quality.
Tip: Toads are excellent pest-control agents, and they will breed in the smallest backyard pond. Toads consume insect pests and larvae, as well as slugs, mosquitoes and flies. In three months, a toad will consume as many as 10,000 insects. Toads are terrestrial creatures that burrow in the earth during the day and come out to eat at night. During the winter, they hibernate in the soil. When breeding, they seek water to lay their eggs, out of which hatch tadpoles that swim around for a few weeks before becoming toads that seek out dry ground.

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