Pruning can be as simple as pinching a flower bud off a chrysanthemum or as radical as sawing an overgrown shrub down to a few stubs.  It is one of the most common garden chores.  Yet many folks are unsure of how or when to do it.

Pruning may be done for several reasons:  to control or reduce plant size, to refine plant shape, to enhance plant health, to stimulate or to inhibit growth.

Each purpose may require a different procedure or pruning time.  When we better understand what it is we wish to accomplish, we should feel more comfortable with the procedure.

Pruning for size

Most plants will grow to a size that is incompatible with their planting site or intended use.  Its not the plants' fault.  It is usually due to faulty planning.  Nevertheless, something must be done about it after the fact.  Therefore they must be pruned periodically for size control.

The simplest way to do it is to trim frequently.  This maintains a neat shape as well as a reasonable size.  Trimming for size control can usually be done at any time of year, as far as plant health is concerned.  Because the pruning cuts are minor, the plant is not stressed.

Long-neglected plants that have become overgrown require radical measures and greater care.  Large shrubs, for example, may be cut down to within 12" of the soil line during late winter or early spring.  Earlier surgery would leave ugly stumps in the landscape for several months before.  Also, such pruning may result in severe plant damage or death from coming cold weather and defoliation.

Pruning for shape

Pruning for shape can usually be done at any time of year.  Again, because the pruning cuts are minor, the plant is not stressed.  Before making the first cut, carefully consider plant growth habit.  Does it lend itself to the shape you wish to achieve, or will you fight a losing battle?

Consider whether the desired shape will enhance the beauty AND health of the plant.  Plants that are too wide at the top will shade the lower portions from sunlight.  The lower leaves will fall off, and the result will be something resembling a hedge of green umbrellas.

Assess the plant shape in relation to its surroundings.  Will it complement the nearby building and neighboring shrubs?  Plants should never be so showy that they detract from their surroundings, nor should they be drab.  Plants shouldn't cover up a building, unless its worth hiding.

Pruning for health

Pruning for plant health may include preventative measures as well as corrective.  Crossing limbs will eventually rub against and damage one another.  Pruning out an offending branch will correct the problem.  Suckers arising near the soil line should be removed.  Dead, damaged and dying tissue may be removed for the health of the plant, and anytime is appropriate.  The sooner the better.

When pruning diseased tissue, cut well back into healthy wood, making sure all infection is removed.  If your cutting tools contact diseased tissue, it is a good idea to sterilize them with flame or alcohol before cutting into healthy wood.  Always be careful to avoid contamination.  Remove and destroy infected plant material.

Broken and damaged branches should be cut back to the main trunk or the nearest limb, removing stubs and jagged edges.  If left, torn edges and stubs will rot back into healthy tissue.  Also, such places allow entry to insects.

A secret to avoiding leaving dead stubs is to prune back to an area where regenerative tissue in abundance can heal over the cut.  Such areas are usually found at nodes (those places where leaves or buds appear along the stem) and at the base of branches and limbs.  If you look carefully at the place where branches and limbs grow from the trunk, you may notice a swelling or collar that surrounds the branch.  The collar is full of regenerative tissue.  If you cut back to that point, leaving the collar intact, the regenerative tissue will grow over the cut and heal the wound.  If pruned too far away from the collar, the stub will die but remain to prevent the wound from healing over.  If pruned too close to the trunk, the regenerative tissue will be removed and the would may not heal at all.

Pruning for growth

Pruning can stimulate plant growth.  This is helpful in cases where older plants need rejuvenation, when planting young trees, or when any plant has not grown adequately.  Such pruning is best done in spring.  As the year progresses, the resulting regrowth is slower.  It is best not to prune for rejuvenation after mid-summer.

Plants that respond well to rejuvenation pruning include roses, clematis, most deciduous shrubs, and young trees.  Conifers, some broad-leaf evergreens, and some older trees don't respond well.  It is better to rejuvenate plants with light, frequent pruning.

Pruning can inhibit growth as well as stimulate it.  The trick is in the timing.  Since rapid regrowth tends to occur in spring, pruning to slow plant growth is best done in fall.

A few more considerations

There are many reasons and seasons to prune plants, but some principles generally apply.  Pruning cuts can be safely made to the following points:  a) above a healthy side branch, b) above a healthy bud, c) to a main branch, or d) just above the ground.  Pruning cuts should not be made too close or too far away from these points.  If too close, the near bud or branch may be damaged.  If too far, it will leave a stub to look ugly and rot.  It is best to cut about 1/4 inch above the bud.

As mentioned before, avoid pruning back flush to a main branch or trunk.  Doing so may damage or remove the ring of regenerative tissue at the base of the cut, and the cut would may be slow to heal.

Prune back to buds or branches that face outward.  Inside buds will grow toward the center of the shrub or tree.  Those branches will cross and damage one another in the future.

Removal of heavy limbs from trees should be done in three stages.  First, cut under the limb about halfway through it, and several inches away from the trunk.  This will prevent the falling limb from tearing off uncut tissue on the bottom of the limb.  Second, cut on top of the limb just beyond the lower cut.  This will sever the limb.  Finally, remove the stub back to the regenerative collar.

It is best not to apply pruning paint or sealant to pruning cuts.  Doing so was a common practice in the past.  It was thought that painting the cut would seal out moisture and prevent rotting.  But plants are mostly composed of water, so instead of sealing moisture out, painting actually seals it in and slows down the healing process.  Some gardeners are convinced that sealing is necessary.  All agree on this:  if sealing pruning cuts makes you feel better, do it.

For specific information on pruning particular types or styles of plants, call your local Cooperative Extension Service.

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