Congdon Gardens Education


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Pruning Pointers for Flowering Shrubs

Pruning is one of the most important, and easiest, techniques to promote healthy, balanced growth and increase the production capabilities of flowering shrubs. So…how do you get started in the, often intimidating, world of pruning?

Before picking up any pruning tool, understand the plants you plan to prune.  If you know the scientific names, a good reference source, – purchased, library or online – will allow you to quickly research and understand the expected growth habits.  A good example is The Manual of Woody Plant Material by Michael Dirr. If you can’t identify the plants, observe the growth cycle of the plant, over an entire year, to determine when and how to prune.  For these unknown plants, watch and note flowering period, where new growth occurs, if suckers form around the base, if it is a single trunk or multi-stem plant, or if there is a graft union present.  Once you have determined when the plant flowers and how the structure is supposed to look you can begin to plan your pruning timing and technique.

Timing is crucial in pruning for continued flowering success. Generally, for flowering shrubs, buds are set after blooming so pruning should be done shortly after the shrub has finished flowering.  Summer and fall flowering shrubs develop the buds throughout the growing season prior to flowering so pruning in late spring may reduce or eliminate flowering.   Some plant materials flower on first year growth, some on second or subsequent year wood.  Unless you are very familiar with determining the age of woody tissue, follow the general rules (yes, there are always exceptions).

Also important, in timing any pruning activity are the intended results.  Pruning to encourage increased vegetative growth is best achieved very early in the spring – after most of the intensely cold weather threats have passed but before the new leaves have emerged in the spring.  Controlling growth and managing plant size is most successfully accomplished through summer pruning – after the new growth has emerged.  Summer pruning should be done before the end of August in our area, as any pruning done later than that may open the newer, tender vegetation for early frost damage.

There are many different growth structures, knowing the basics of how to address multi-stemmed and single stemmed plants will get you through.  Multi-stemmed shrubs are those that have many branches emerging from the ground (often referred to as suckers), two commonly found examples are Syringa vulgaris (shrub lilac) and Cornus stolonifera (red twig dogwood).  These can easily be pruned with a technique called renewal pruning, which is to remove about 1/3 of the total branches, generally the oldest, at the ground level.  This will promote new healthy growth; and in the case of Cornus stolonifera, that new red colored growth is more attractive than the old gray colored growth.

Do not use renewal pruning techniques for single stemmed shrubs – you may be left with a stump.   If you have a shrub that has a graft union (many roses do), do not prune off the plant to a point beneath that graft union.  Grafted plant material is made up of two separate plants – one at the root level that has strong growth characteristics and one above the ground that has the desired ornamental characteristics.  If you eliminate the top plant, you will have eliminated the part of the plant with the most desirable ornamental characteristics.

Once you have the appropriate information on the structure and habit of your plant materials, and you have determined the appropriate timing to meet your pruning goals – you are ready to pick up that nicely sharpened, disinfected pruning tool.  First – take notice of any branches that are dead or out of sync with the overall shape of the shrub.  Remove those with a nice cut made somewhat perpendicular to the ground surface.  It is very important that you get close to, but do not cut through, the branch collar (this looks like a mock turtleneck on the branch joint).  If you are removing only a portion of a branch you can determine where to make that cut by looking at the positions of the remaining buds on the branch. If the bud is on the outer side of the branch, facing outward, branch growth will be directed outward.  If the bud is facing the interior of the shrub, growth will be encouraged in that direction.  When making a pruning cut, angle the blade at about 45 – 60 degrees, following the angle of the bud, about ¼” above the nearest bud growing in the direction you want the branch to grow.

Now, look again at the shrub.  Any crossing or rubbing branches will be detrimental to the strength of the overall structure and they may be causing open wounds on the branches.  Any continually rubbed wounds will not callous over and become open invitations for insect and disease problems.   Remove at least one of them to alleviate the rubbing problem.   If you notice any branches that have puzzling symptoms or potential disease issues, you may want to have a professional look at them before you do any pruning.  Proper care will help to prevent the inadvertent spread of any problems.

You have taken the first steps into the world of shrub pruning.  Once you have gotten to this point, the rest becomes much easier.  After the initial pruning cuts made for plant health, the rest of the pruning exercise is for shape, growth, and control.  Most plants are very forgiving – and they will be more appreciative for a bit of care than complete neglect.  Give pruning a whirl.  You may be surprised with how satisfying it is.