Pruning…Why do we do it? Cutting Woody Plants Down to Size

The Pruning Series, 2

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This Fagus sylvatica has been in this pot around 20 years. I grew it from seed 30 years ago from a mother tree in Sellwood that has a canopy 100′ across. It is approximately the same age as the trees pictured below.

I’ve heard it said often enough that trees and shrubs got by just fine for millions of years before we started pruning them, so why do it now?  That’s a good question and if you can’t answer it, you shouldn’t be pruning.  Horrible examples are all around us.  Trees repeatedly stubbed off their natural branching form and elegance destroyed.  Others sporting long scars where someone removed a branch with a single top cut causing the branch to drop pulling a long tongue down the trunk where it was still attached.  Still more with split trunks and scaffold limbs where multiple sprouts, vying for dominance fail and tear down.  Poor pruning has lead to the collapse and premature deaths of many trees and reduced many shrubs to inelegant space fillers jammed up agains buildings.  The first thing you should ask yourself is, ‘Why I’m I doing this?”

Why, can be the most exasperating question…especially when it comes over and over again from your child.  There is something almost primal about.  It can go to your very core and raise doubt, if you have not give it enough thought previously, if you have not already worked it out for yourself.  For many of us it feels confining, restrictive…limiting…maybe even threatening.  It can quash our spontaneity and is often not welcome…kill our creative impulse.  When people ask me about pruning a particular plant or just in general, I always ask them, why?  Why are you pruning that specific plant?  Why are you choosing ‘that’ branch and not this one?  Why are you cutting it at that bud, or lateral?  Why between nodes?  Why don’t you just leave it alone…and cut this one?  If your answer is indecisive, then don’t cut it.  When pruning you should know why you are making each cut.  There are many valid answers to this question.  Why begs that you have considered intent and goals.  What are you trying to do? and will each decision along the way move you closer toward that goal, ideal or vision?  To answer requires that you ‘know’ the plant, how it grows and how it will respond to your pruning.  If you don’t know then that should give you pause.  I have met many people who are intimidated by pruning.  It has remained a ‘mystery’ to them.  they watch others do it and it doesn’t help.  They appreciate the job well done, but there is something essential that they miss.

Pruning is a reductive art, like sculpture, only when sculpting wood or stone, when shaping plaster or clay, when the artist is ‘finished’, the piece is static and remains fixed, only responding to erosive forces or perhaps developing a patina.  Plants, however, are alive.  You cut them into a particular shape or form and they quickly begin to grow, when the season allows, into something else.  An experienced competent pruner can prune creatively making cuts that encourage growth that fits both the genetic pattern and their own image of the future plant.  They can do this because they know the plant and how it will respond.  It is not a haphazard or random process.  It is a dance and you cannot coax your partner into something they cannot do.

Controlling size is often a primary driver in pruning as are aesthetics ranging from naturalistic, to the highly stylized such as Bonsai, to the formality of hedges and topiary.  Others may be pruning to maximize fruit production on ‘free standing’ trees or creating a trellised system, while another person is training and maintaining their fruit trees into formal espalier.  Another is walking the line with Wisteria training it on a supporting frame attempting to limit its powerful shooting and sprouting while maximizing its floral display.  For others it is all about maximizing bloom.  With many plants, especially those that form a strong branching structure, we are attempting to create/support its formation removing what would weaken it.  Whenever we prune, all of us, should be aware of the plant’s current state of health and doing what we can to support it.  What is ‘good’ for a plant in terms of health, is generally ‘beautiful’ as well.

Very often the answer to ‘why’ is simply to limit a plant’s size, to contain it.  It will grow too big, or so we think.  It will crowd a path, the road or driveway or it will over top our house and pose a threat should it fail dropping limbs or perhaps splitting or toppling over crushing it.  In other instances, we believe that it will grow out of scale and dominate neighboring plants or the landscape in a way we don’t want or will shade out other desirable plants.

If size is the issue, we should ask ourselves several questions before we begin, does its size really pose the hazard that we believe it to?  Do we know the species or cultivar and how it grows?  Is it possible to aesthetically limit its size? or will it simply look butchered?  Some trees tend to have weak structure or are more prone to breakage than others, is yours?  If a tree overhangs a structure it does not automatically pose a risk to the building.  You must also be aware that some types of pruning actually create situations that are more hazardous than when a tree is left on its own or pruned in a way that is consistent and supportive of it’s normal growth habit.  In particular heading back cuts tend to lead to heavy sprouting.  The shoots that result from heading cuts are always more weakly attached to the tree’s trunk or scaffold branches and as such are more prone later to failure.  Cutting a tree or shrub hard increases sprouting often producing vigorous shoots that quickly reach the size the pruner removed originally.  Trying to contain a plant within a space that is much smaller than its ultimate size commits the gardener to a never ending regime of pruning and control.  When these plants are trees this commitment may quickly prove to be more than the typical gardener can deal with.  Their size creates potentially hazardous conditions for work.  This may encourage many to make large ‘heading back’ cuts deep within the tree’s structure simply because it is safer for the pruner and they can more easily reach these places with their saws.  These large cuts can be very slow to grow over, taking years to ‘close’ and remaining as avenues for the entry of rot within the tree.  Such pruning can hasten the early decline of many different species.  If a plant really is too large for the space removal is often the best solution.

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These two Fagus sylvatica are in the South Park Blocks where Salmon St cuts the blocks off on the north end. These were planted here around ’88 from 1-1/2″ or so BxB stock. They are well over 50′ tall.

There are other strategies that can be much more effective for limiting the size and shape of a plant than large heading back cuts.  The most effective is to plant a species or cultivar that will ultimately fit the space and possess the desired structure and texture you want in the first place.  Plants should fit both the growing conditions presented by a site and fulfill the aesthetic characteristics that we desire, however, not everything always works as planned.

Plant size can also be limited by growing conditions.  Stressors such as drought and limited availability of Nitrogen can shorten internodes, the spaces between vegetative buds, as well as leaf size.  In other words, it can have a dwarfing effect.  Too much drought and plants will be stunted to an unhealthy degree often resulting in crisped leaf edges, premature leaf drop (Remember that some California natives in particular, are drought deciduous, routinely dropping their leaves in mid-summer without unduly stressing the plant.  Plants from other summer moist climates may actually be harmed by such drought.) When conditions are optimum, however, growth is vigorous.  To some degree plant size can be controlled by irrigation practice.  For me this is what I do with my Bananas.  I keep them just moist enough to prevent ‘burn’ along the margins.  Musa basjoo and M. sikkimense can reach over 20’ here if they don’t freeze down and they get steady water.  Woody plants too can be controlled somewhat this way.

Many species of woody plants can be limited by growing them in pots.  Some, however, are not tolerant of this in the longer term.  Pots limit the available soil volume and in so doing their nutrients and water.  The soil volume is also subject to wider, quicker, swings in soil temperature which may be poorly tolerated by some species.  We’ve all seen amazing Bonsai dwarfed by very specific techniques including limiting soil volume, strictly limiting nutrition and maintaining a moist but very limited soil volume.  Pruning and training are a refined art for these.

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My hand against one of the two South Park Blocks Beech trees. As young trees these can grow quite quickly.

I have a 30 year old Fagus sylvatica, European Beech, that I grew from seed, I’ve kept in a pot its entire life, periodically pulling it out, pruning its roots and replenishing the soil.  Beyond this I only lightly fertilize and prune it and have never trussed it up with wire to get a branch growing how I might want it.  I let the plant choose.  Were this tree in the ground it would have long ago exceeded any space I have for it.  Many species include grafted varieties that are more dwarf than the type.  If the gardener is committed to including a particular species it might behoove them to look at dwarf selections if their space is limited, as long as the plants growth habit will provide the form and structure the gardener is looking for.  Many dwarf cultivars have very different forms than the species type and no amount of pruning will make them look like a small version.  A weeper or a mound growing form would require so much pruning and training as to make it practically impossible.

Other gardeners attempt to limit size for ‘security’ reasons.  Open sight lines.  In the early ’90’s there was an organized effort to promote so called security pruning, CEPTED, Crime Prevention Through Environmental Design.  Especially in its early years this translated into an effort to develop simplified pruning standards that recognized the perception of safety as the highest priority.  In Parks this lead to all kinds of conflicts.  Most of our plantings were decades old and so were mature in stature.  We were often directed to open sight lines converting many broad leaved evergreen shrubs into ‘flying saucers’ with their bases bare of growth and their height strictly limited to eliminate hiding places from which would be attackers might pounce.  Lighting was increased.  Police wanted to be able to scan a Park from the road or the Park’s path system.  Many of us tried to refuse and instead of ‘butchering’ and uglifying a plant argued to remove them and plant something whose form would not create any such conflicts.  If pushed to its absurd maximum we argued that this policy would eliminate any shrub and low mixed plantings destroying many of the aesthetic reasons for having public Parks in the first place.  While Parks has come to a more balanced approach to this much of the public is still caught in the simple early and brutal stages of this practice with its ‘traumatized’ plants.

I did this planting of Rhapholepsis indica (?) some 15+ years ago the vacated portion of SW Mill St downtown immediately west of Pettygrove Park. There are 3 beds here all once planted on a cycle with annuals and bulbs. The annuals program was cut and planted all three beds in smaller shrubs. At some point the properties north and south had new structures built on them and the beds were removed from Parks care. The Hamamelis 'Arnold's Promise' was hacked off at around 5' several times destroying its upright vase form until more recently it was cut nearly to the ground with the more random sprouting here resulting.

I did this planting of Rhapholepsis indica (?) some 15+ years ago on the vacated portion of SW Mill St downtown immediately west of Pettygrove Park. There are 3 beds here all once planted on a cycle with annuals and bulbs. The annuals program was cut so I planted all three beds in smaller shrubs. At some point the properties north and south had new structures built on them and the beds were removed from Parks care. The Hamamelis ‘Arnold’s Promise’ was hacked off at around 5′ several times destroying its upright vase form until more recently it was cut nearly to the ground with the more random sprouting here resulting.

For many people, the uninitiated, the inexperienced, the tendency will be to allow a plant to grow on its own until it reaches a size considered too big and then it is simply cut back to a more acceptable size.  This is the practice of many commercial maintenance companies.  It is applied to a broad array of shrubs, most typically those that grow in an arching, fountain form (All too often I see Rhododendron, Camellia and Pieris used as foundation plantings that are regularly and brutally cut back leaving little of any aesthetic value, serving only as space fillers.) that typically produce new basal shoots prolifically though it can also be done to plants that tend to produce a more structural and long term form even including plants like Hamamelis and Hibiscus syriacus!  It requires less experience and knowledge from staff and results in a more ‘one size fits all’ approach regardless of a particular plant’s natural form.  Often each plant is thus also separated from all of the others.  Such pruning appeals to both those with needs for ‘neatness’ and uniformity and those with an over riding concern for cost.  Many shrubs can have their size controlled by pruning without resulting in these stiff truncated forms.

Shrubs that typically initiate their growth from the base of the plant arch out in a ‘fountain’ form and can be ‘rejuvenated’ on a cycle cutting the whole plant to the ground once every few years or by selectively removing a 1/4 or 1/3 of the older and/or weaker stems each year. The bases of such plants increase in diameter over the years as do many clump forming plants including herbaceous ones.  Plants like Abelia x grandiflora can get quite broad and, if planted too close to paths, can over whelm them in time.  Others like Forsythia can do this even more quickly.  Both can be well behaved garden members for many years with a little pruning.

Forsythia has the habit of growing long lanky stems, arcing down to the ground and touching it where they can layer, forming roots, spreading the mass of the plant, sending up new shoots from these new crowns.  To maintain some semblance of order and maintaining the integrity of a garden’s design, or assuring the survival of neighboring plants, I would prune these annually, removing weak horizontal growth, uprooting and removing the layered tips and making other cuts to maintain the upward arching form.  This could entail a lot of cutting which I would do after blooming.

Plants like mature Abelia have very congested crowns in which selective removal is extremely time consuming and difficult.  For these I might cut the whole thing to the ground forcing new growth with a softly arching form, rejuvenating the whole plant every few years.  I’d do the same for mass plantings of Spiarea.  If there was only one, like S. x vanhoutteii, I might do the three year cycle to bring it down in size and then leave it alone for a few years, depending on how much room it had and the overall effect of the landscape.

With others like Rose glauca, once they reach mature size, it was not so much the size of the plant that concerned me, but the size of the ‘wood’ within it.  Over time it would increase branching, bulking up and with decreasing floriferousness.  I would remove a quarter to a third of these large old stems to keep the overall plant vital as well as the weaker side shoots.  Was this ‘natural’? Not really, but the plants could other wise become so ungainly that they detracted from the garden and did not fill their aesthetic ‘role’.

Other times trees were planted in a landscape that were never intended to attain tree form.  These might be routinely coppiced, preventing the formation of a trunk, encouraging  instead a flush of vigorous stems clothed in over large leaves.  This may be done with Cotinus, Paulownia and Catalpa.  This is not random thoughtless hacking but is pruning done to create a specific desired effect.  Pollarding is a similar technique practiced on a formal branched structure.  It is not an annual hacking back of growth but one that respects the genetics of its subject and its ability to respond to the treatment over the years.  Wound size is minimized so that rot is much less of a factor.

Some trees, like genus Pinus, produce their new growth typically in whorls of branches and have dominant shoots or ‘candles’ that grow out from the tree’s leader and side branches.  These ‘candles’ emerge and lengthen early in the spring gradually hardening off.  The ‘candles’ can be snapped or pinched off at an early stage by hand, shortening the internode, the distance between whorls, dwarfing the tree.  The same effect cannot be made by allowing the candles to extend fully and periodically pruning/ reducing using a saw.  The saw technique, will result in a smaller plant but with the full length internodes the plant will be more ungainly and out of scale within its canopy.  Utilizing this technique creates less of a wound for the plant to ‘deal’ with.  Some Pinus species are very vigorous and may be more prone to damage in climates that are subject to heavy wet snows and freezing rain.  ‘Candling’ them, in such cases, can make them more sturdy as the new growth is shortened.

Too often I see trees and shrubs, poorly chosen, in terms of their ultimate size, for their particular placement.  Left for a number of years on their own they grow to the point of being a problem before anyone attempts to address them through pruning.  Often times these may be plants that could have easily fit within the space had they been so maintained.  Left on their own, now they require a much heavier ‘treatment’ or removal.

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This is a Ribes sanguineum down the street from my house that the owners have tried to keep in bounds. The other shrubs are pruned in the same manner. You can see the oldest structure at the base and then moving up it has be prune hard twice, each time ‘releasing’ more buds to grow making the top denser and into a flat top as their cuts are mostly in a horizontal plane and they’ve made no thinning cuts.

Pruning is the assiduous infliction of ‘wounds’ upon a plant intended to limit or control a plants growth to a desired effect.  Wounding.  It is different from storm damage and vandalism in that this wounding is simultaneously intentional and applied in such a way as to minimize negative effects for the plant.  For those that argue that such practice is un-natural and to be avoided, it should be remembered that nature prunes in her own way and its results can be considerably more course and brutal.

Pruning is a necessary part of the ‘human’ landscape.  We are invested in these plants.  We are in relationship with the plant members of our landscape community.  Their presence effects us as will their departure, not unlike our children.  Is this healthy?  It is certainly natural/human for us.  Nature does not form this kind of natural attachment to individuals.  In the ‘natural world’ huge limbs may tear down the length of a tree’s trunk crushing neighbors, while leaving large ragged wounds and shattered stubs behind, that may never be ‘closed’ by the tree, leaving entry points for disease and rot.  Nature also prunes by ‘shading out’ branches in their interior where deprived of light they have eventually shut down their ability to photosynthesize transferring such activity to where sunshine is more available. This leaves dead branches which will eventually drop, but generally not ‘cleanly’, again providing avenues for disease or rot into the living plant.  A heavy ‘burden’ of dead wood possess a potential hazard to the plant. It also ‘prunes with  storms that torque and tear branches; that weigh down limbs with ice or snow beyond their ability to hold; or simply split and rend trees as a result of their own weight levering open a weak point of attachment.  Nature works to protect the whole, the population, not the individual, whereas through pruning we seek to protect ‘our’ tree or shrub.  We want it to be beautiful.

We need to be thoughtful and informed if we are to be successful in terms of both goals, health and beauty.  The same cut made on one plant may be problematic on another plant, its timing, precise location and size can have very different ramifications.  We must consider the plant first.  Our goals, and our efforts to reach them, may pose a threat to the longer term health and viability of the plant….Depending on the circumstances, one’s goals, this may be ‘acceptable’.  Under natural conditions plants are limited in their size, these limits are often not the same that we would impose.  Pruning begs the question, ‘What is natural and what is our role in the process?’  Pruning is an intervention.  How can we best do it while minimizing negative consequences for the plant?

Please see my previous posting on pruning tools which covers some basics of pruning.  There are more posts on pruning to follow.

 

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