The Pruning Series, 3

Plants often present pruning challenges to the gardener.  I’ve already introduced the issue of understanding ‘why’ you are choosing to prune, the physical structure of a ‘normally’ growing individual and how it will respond to the cuts you choose to make.  There are several good books out there that discuss how and what constitutes a ‘good’ individual cut and what approach you might take with different types of growers…it should be the goal of any gardener to understand the technical details of pruning, so that they become ‘natural’, reflexive. (In an earlier posting, I discuss pruning tools and provide an introduction to what constitutes a ‘good’ pruning cut.) Like all artists we develop a style that may distinguish us from others.  Even understanding all of this and possessing the technical competencies there are the ‘aesthetic’ decisions the gardener/pruner must make.  Two different gardeners can prune in the same landscape and it can be obvious when they are finished that they have very different aesthetics.  The results can be ‘disjointed’ or harmonious.  Every plant, every branch, every internode, presents a choice and because each individual plant of a given species or variety, though it may grow following a shared genetic code, will grow uniquely in response to the physical conditions it faces…and the damage and pruning it has received over its life.  Like most things in life our control of a plant is limited and the more we attempt to control it the less like itself it will be.

Shearing is a practice, well founded in horticulture, that gives the gardener the most ‘control’ over a plant cutting it to a uniform shape to fit the formal, rigid vision that we may have for it.  Its response, of course, if it is a plant that is indeed tolerant of shearing, is an explosion of seemingly random growth with stems erupting in every direction other than into its darkened interior.  Another gardener may choose to ‘round off’ a shrub at a given height with shears in an attempt to limit its size.  A third may approach it with an eye looking to maintain more of its natural, genetic driven, form.  This is the more selective, time consuming approach where cuts are made at particular buds or at the base of a branch (thinning type cuts) removing a branch, stem or shoot, wholly, while leaving another to reinforce the natural branching habit or pattern while at the same time reducing the overall size of a plant and/or opening it up, reducing its density.  Shearing and heading back, as described above, lead to more congested growth and, if practiced over time, results more likely in a plant with a thin dense ‘shell’ of foliage covering a bare ‘twiggy’ interior.  Done side by side or from bed to bed these contrasting ‘styles’ give a more disjointed overall appearance.  If practiced over the years shearing  or topping can cause problems, particularly when a ‘natural’ style pruner follows.  In these cases the natural branch lines are disrupted and the interior can be very congested, containing more dead wood from having been heavily shaded while the living branches may be too crowded and don’t possess that ‘natural’ look.  Regaining a natural form can take years of ‘corrective’ work and regrowth.

There are of course those plants that normally grow in a more ‘congested’ pattern, including many shrubs that form an upright arching or vase form while regularly producing new shoots from the base like the Spiareas, Barberries, Philadelphus, Forsythia, Deutzia, etc..  Others, like many, generally smaller trees, form congested ’round canopies, with a branching habit that can be defined as more random than structural and graceful.  These include the Crabapples, Malus, and Hawthorn, Crataegus, among others. These don’t form the more elegant and ‘permanent’ branching structure of other shrubs like Camellia, Rhododendron or the many forms of Japanese Maple.  Pruning vase or fountain forming shrubs in the time consuming ‘natural’ style i’ve described above can ‘suck up’ a lot of time.  A different approach may be called for with these.  Ideally, these would be ‘renewed’ either by removing a percentage of the old growth at the base annually or, if that is too difficult, because of the number and density of basal shoots, cutting the entire plant down once every three years or so so that it can maintain both its floriferousness and its ‘softer’ form.  The more random branching trees can be a great frustration to the pruner if one’s goal is to train them into a graceful single leader tree.  the pruner must remember that heading back or shearing trees like these will result in an even more congested form and change the natural silhouette.

Specimen, architectural plants whose permanent woody structures are a primary feature need to be pruned in a manner sensitive to their structure.  These plants tend not to be strong basal sprouters unless damaged or pruned ‘hard’ or cut very low.  Each year new growth is dominated by terminal growth, additions to the existing branch structure,  with lesser growth from laterals.  Growth ‘builds’, accumulatively, on previous growth.

All ‘vascular plants, regardless of their natural overall form, will have either an alternating or opposite bud arrangement on newer growth.  This arrangement strongly effects the pattern of growth.  Alternating buds will tend to result in a zig-zagging pattern for each branch.  Opposite buds will form opposite, symmetrical, shoots along the extending branch (like Japanese Maples).  Simply cutting them back without consideration of the new growth, especially repeatedly, can result in clumsy, blunt, branching with many ‘dog-legs’ and branches growing across or through a plant being very visually conflicted with the plant’s form.  Poor pruning can destroy their form.

This artful aspect of pruning requires time and guidance to develop. It is an additional skill that must be learned beyond the more technical aspects of simply making a ‘good’ cut or even of understanding the plant you are working on.  Pruning is art and science.  To do it well requires study and practice.  I highly recommend that all gardeners take a class or two from their nearest Community College (both Clackamas and Portland Community have horticulture programs intended for the training of professionals in the field.  They can give you a thorough understanding of the work and provide some field experience.)  It would also be beneficial for gardeners to find a ‘mentor’ that they can prune with to learn from.  Good pruners are not ‘born’.

Pruning aesthetics are closely related to the design of the garden or landscape.  Many or most designs are a blend of informal and formal elements while others range toward either extreme. Very often, even in a naturalistic garden designers will place a formal element, sometimes sculptural, sometimes a plant, as a conscious focal point.  The same can be done in a formal garden, done well, for example, with a soft form spilling over and across a very formal clipped parterre.  Changing how such elements are pruned will detract from the designers original intent.  Allowing a formal clipped landscape to ‘devolve’ into softer/ wilder form will both change the ‘experience’ for the visitor or viewer and quite likely lead to the problem of many of the so ‘released’ plants over whelming there neighbors and crowding the space intended for visitors.  It can result in the dominance of larger more aggressive plants over their less so garden bed ‘mates’.  At the opposite end, shearing or hedging plants intended to fill the space with their spreading natural forms can create a stiff, lumpy landscape with plants separated in space looking awkward.  We’ve all seen landscapes where the gardener/maintenance staff seems driven by a need for ‘neatness’ with each plant controlled and limited, separated from each other.  This is often accompanied by the clean ground approach free of weeds or organic debris of any kind.  The later seem to be landscapes in which owners or staff barely tolerate the presence of plants (My bias is showing!).  Design and pruning are intimately and directly link.

Many of us, given our proclivities, tend to be collectors and are less concerned with garden design, never the less, we should keep in mind that how we prune, our consistency and aesthetic, affect the look and ‘feel’ of our gardens and because of this are very important to their ‘success’ and our experience in them.

While maybe not an issue for the home gardener as you are not working with others whose approach may conflict, the issue of style or pruning preference, can be a large issue in organizations such as Parks.  It was for us in Portland Parks and Recreation.  It sometimes became a divisive point of contention.  As a group the horticultural staff eventually got together and worked this out producing a document that would guide us in the future.  Management bought in and agreed to make this part of the formal introduction to new field staff.  As is too often the case, however, management has other priorities and this quickly fell into disuse.  This document was also produced independent of the Forestry Division, part of Parks, another old pattern.  Again management is unaware of horticultural issues and often under values them in pursuit of its other priorities.  An inevitability in any political organizations, I suppose, but exasperating all the same.  I’m including the document I drafted, in committee, as part of Park’s ‘irregular’ Quality Circle meetings, adopted by Park’s management.  It is a guide for a staff that was already very experienced at pruning, not a basic ‘how to prune’ guide.

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Portland Parks and Recreation

Pruning Standards and Guidelines:

Towards a Sustainable Practice for Horticultural Staff

January 2008

This document is intended to be used as an introduction for new service zone staff and as guidelines for work done on a day to day basis.

The following references should be available at all zone maintenance offices and used to implement proper pruning techniques:

American Horticultural Society:  Pruning and Training,  Christopher Brickell 1996

The Royal Horticultural Society:  Pruning and Training,  Christopher Brickell and David Joyce 2006

Pruning should be consistent with good horticultural practice.  Good horticultural practice promotes the health and vigor of plants, and increases the value and beauty of the landscape.  The goal is to maintain natural plant forms and avoid extreme practices that lead to increased maintenance.  In a well-designed landscape, trees and shrubs are placed where they can attain their mature size and form without severe pruning.  Severe pruning does not correct a poor design – removal and redesign does.

Why We Prune

    Routine pruning 

        –  to maintain good form and keep the plant’s growth within the space available to it

        –  to allow for showy display of bloom or fruit

        –  for ease of maintenance

        –  for removal of dead, crossing, weak or diseased wood

        –  to provide for good air circulation and light penetration

        –  to keep plants balanced and centered over their roots for sturdiness

        –  for renewal when necessary

Training

        –  to establish proper framework for young and newly planted plants

       –  includes the removal of competing leaders on trees and (except conifers) good separation   between laterals

For safety

        – thinning for visibility throughout the plant

        –  to reduce a safety threat to both staff and the public

        –  the Horticulturist responsible for the area will decide what type of pruning is acceptable, or if the plant should be removed and replaced with something more appropriate

Corrective and hazard pruning 

         –  done as a result of physical damage that may present a hazard to people or a threat to the plant’s health

         –  corrective/hazard pruning may so compromise the structure and beauty of the plant that removal may be a better option

Pruning Techniques

    Desirable Practices

        Thinning cuts

            –  cuts made along the branch just above a healthy vegetative bud or branch

           –  results in fewer buds growing in a congested manner than a heading-type cut

          –  results in an overall appearance that is more graceful and “layered’ in a ‘natural’ manner

         –  can be used to reduce the size of a plant and/or to open it up for plant health and visibility

Renewal pruning

        – when needed removing 1/3 of the growth annually from the base keeps a shrub looking better throughout the year

        – some woody plants loose vigor or are less floriferous as there stems age and require removal

        – many woody plants have a naturally elegant branching structure, bloom on older wood and/or look best with some ‘permanent’ structure and should not be cut to the ground

        – cutting a plant to the ground results in lush soft growth and generally requires follow-  up pruning

Routine pruning

        –  most plants are easier to keep pruned on a regular schedule rather than allowing them to get out of hand

        –  this is the best way to maintain manageable size and elegant form while assuring vigor and a floriferous habit

“Limbing up”

        –  selective removal of lower tree branches that conflict with pedestrians and vehicles

        –  if not removed these branches can be injured, causing more damage than careful removal

    Undesirable Practices

        –  severe pruning is never desirable; it ignores the natural growth habit of plants

        –  it may shorten the life of the plant, decrease the value and cost more in future maintenance or replacement.

        –  it may stimulate vigorous growth that can weaken the structure

     Forms of severe pruning:

       Heading back

        –  these types of cuts leave a stub – stubs are never acceptable

        –  these cuts are generally not consciously made to a bud or branch growing in a desirable direction

        –  produces an unnaturally uniform appearance resulting in congested sprouting

      Shearing  (a common practice in the landscape industry)

         –  reserved for formal elements in a landscape – appropriate for a hedge or topiary, not individual shrubs in an informal landscape

        –  labor intensive – stimulates bushy regrowth, contributing to higher maintenance

        –  heavy sprouting at the cut ends shades out the interior; creates a ‘shell’ of foliage around the perimeter of the plant with little live foliage inside; plant health eventually deteriorates

        –  restoring a repeatedly sheared plant to its natural form is very difficult and time consuming, if not impossible

     “Low Limbing”

        –  in practice, can become an arbitrary removal or stubbing off of lower branches to satisfy personal preference or some idea of uniformity

        –  lower branching tree species should be planted in beds where traffic conflicts cannot occur

        – conifers grow symmetrically with strong branches and a whorled branching habit.  Many conifers will naturally loose branches as they are shaded out over time.  Any limbing up should be done very carefully, no higher than necessary and should not reveal the trunk for more than 10% to 20% of the trees height. Thinning out the whorls will provide a more natural appearance

Formal design Elements and exceptions to the above practices:

         –  when the design of a landscape calls for regular severe pruning such as formal hedges

         –  includes pollarding or coppicing of specimens in a formal landscape

         –  many roses require annual heavy pruning to keep from breaking and toppling, to encourage an open structure, and renew flowering wood

Final Words

Pruning is a skill requiring knowledge and experience.  ACS, seasonal employees and prison

crews, in general, do not have the skill and should only be allowed to do the roughest of pruning work and removals.  Exceptions may be made on a case by case basis provided the person has been trained and is being actively supervised.

Pruning cannot fix a bad or inappropriate design.  The wrong plant in the wrong place will be a problem and an eyesore as long as it remains.

Past neglect does not justify poor pruning practices today.

Pruning is complex.  It requires horticultural expertise and must be based on horticultural standards.  Plants are an investment, a valuable infrastructure that can be lost without a commitment to good horticultural practices.

I’m adding another book to either of the Brickell titles above Tree Pruning: A Worldwide Photo Guide,1989,by Alex L. Shigo.  Shigo is considered by many to be the best source for information on the technical aspects of pruning and a tree’s response.  He documented his many years of research/practice compiling it in several books, some more technical, others geared for the average residential gardener.  Of course if you have the patience and interest there are some very good general texts on arboriculture that would be of help as well.  Arboriculture: Integrated Management of Landscape Trees, Shrubs, and Vines (4th Edition), Jan 26, 2003 by Richard W. Harris, or one of his earlier editions, is very good.  I still have my copy from school.  Take a class or check it out at the library. Specialty books abound covering technical aspects of such arts as Bonsai, creating and maintaining fanciful topiary and others on trellising and its more refined cousin, espalier in addition to guides covering more standard approaches for trees and shrubs. It would also be beneficial for gardeners to find a ‘mentor’ that they can prune with to learn from.  Good pruners are not ‘born’.

As with all things exceptions abound, but as has been said many times by others, you must know the rules if you choose to break them otherwise you are likely to end up with a mess. In our gardens and landscapes, pruning to achieve a ‘natural’ form, involves our intervention.  Plants left to grow on their own in nature are subject to their site conditions including both the regular and irregular forces active there.  The same plant in our landscapes lead a coddled life protected from these natural forces, e.g., browsing animals and fire, often even from the shading and competition found in forests, woodlands and chaparral. We protect them. Show favoritism as we work to modify conditions so that they establish and grow well.  Nature does not do this.  That gnarled looking Manzanita, the high branching Ash, Maple or Beech, was a result of the competition yours is protected from.  If our goal is a ‘natural’ form we will likely have to prune or the result may be very different than our expectation.  And not just that, it may not fit the space allotted to it nor fulfill its aesthetic role in the landscape.