science based pruning: part 1 – healthy start
In the forest no one prunes the plants and trees – so why all the fuss about pruning? I think my library has six ‘How To’ books on pruning, several illustrated guides and one volume, so weighty, that it is used for a door stop in my office. I have devoted hours to instruction and study of the science of pruning and attended workshops to improve technique. My arsenal of hand tools is impressive and I will debate the merits of Swiss made pruners vs Japanese tools Ad nauseam. I thrill with yearly upgrades in power saws and boast the addition of a battery chainsaw to my ever-growing cache.
With so much information on pruning and technique available – what can I offer you the gentle reader? I have found that most information available is so basic that making the connection to one’s overgrown forsythia or walnut tree planted under the eaves, is not applicable – or so complicated that one would have to dedicate an unreasonable amount of time in deciphering and wading through a search engine results. In the age of fast answers, information, and immediate solutions – few have the patience and skill to prune correctly and to learn and apply the techniques of science based pruning, thus, hasty decisions that often damage or ruin valuable landscaping are the result. So the goal for this series is to focus on the science behind the cut and specifics for the most common plants and problems encountered. There is, or should be, a method to the madness! In addition, I want to cover the basic skills and decipher the information to assist in the preparation for certification in horticulture.
So back to the original question – is it unnecessary or a waste of effort to prune? Consider this: In the forest or wilderness, one in a billion seeds becomes a mature tree. Contrasted with plantings in urban or suburban gardens where the expectation is that almost every tree or plant will make it to maturity. Sound technique and science based pruning can maintain the health, structure, and aesthetics of trees and shrubs. Using a science based pruning program and understanding what needs to be accomplished and why, can help the gardener address defects/problems before they arise, become a hazard, or a health issue for the plant and landscape. It has another benefit also: it saves on resources, time, and money.
reasons to prune: train, maintain, improve, and restrict
I had a conversation yesterday with a receptionist at a medical office. In passing, I mentioned that the container trees on the outside patio (I think they were prunus) were in severe decline. I could see that they had been hacked into submission and the soil was compacted, roots were girdled above the soil, and no doubt water deprived. I apologized, and explained as an arborist not to notice the landscape. I find myself mentally completing a level 1 assessment of any tree I encounter – much like the plumber sees every dripping faucet. She explained that the engineering department cared for the trees and was scheduled to “prune” next week for the fall season. I cringed…not much left to prune on these poor specimens. Most property managers, homeowners, and even grounds maintenance staff lack the basic knowledge of why, when, and how to prune woody perennials.
Reasons for pruning can be grouped into four categories and the techniques and specifics for each reason will be covered in more detail in future installments of making the cut – science based pruning series.
to train a plant
When a plant of tree is first transplanted it should be pruned only to remove dead, broken, crossing, or pest-infested branches. Early pruning, in the first growing season, is to train a tree to develop a strong, well balance shape.
“Contrary to common belief, it is not necessary to prune away one-third of a tree’s top to growth to compensate for root loss…excessive pruning at transplanting, according to research, reduces plant size and does not aid in survival.”Adapted from the Virginia Master Gardener Handbook
to maintain plant health
First and foremost is sanitation. By eliminating dead, dying, or diseased wood you will remove an entry point or build-up area for insects and fungi that could spread to other parts of the plant.
Occasional thinning allows light and air to penetrate throughout the plant, resulting in even growth and healthy foliage.
to improve the quality of flowers, fruit, foliage, or stems
The more flowers and fruit a plant produces, the smaller they are. there is only so much energy and resources to go around! Timing and pruning techniques are used to enhance flowers, foliage and even to enhance bark during seasonal changes.
to restrict growth
Trees and shrubs often outgrow the area they were planted in and pruning to reduce the growth is an option. there are other reasons to restrict growth for design purposes. Formal hedges and topiary are landscape styles that require constant pruning maintenance to retain the desired shape. Also, growth restricting cuts are used to train espalier and bonsai styles.
Remember…the nursery will sell you any plant without question (you should ask, by the way…if you have questions!), most landscape designers are more concerned about design aesthetics then species selection, and some grounds maintenance staff often lack the time and skill to properly install and maintain plants. It is up to the property manager to ensure that the right plant is selected for the right location and that it meets the environment, safety, maintenance, and aesthetic requirements of your plan. This sounds more complicated than it is. Here are a few simple research steps to take before installing any woody perennial because mistakes at this stage can lead to years of costly time consuming maintenance pruning or worse.
Always start your planting project with high quality nursery stock
Over planting and failing to anticipate the mature height and spread of a tree or shrub is a common mistake in landscape design and installation. If plants are to close together there is little room for natural growth and overcrowding requires additional maintenance. Often plants have to be removed or pruned frequently and the method of pruning/cutting back favors shearing (where you end up with lopsided lollipops) rather than selective pruning that enhances natural habit in a tree or shrub. Overcrowding prevents air circulation, which in turn, can promote a garden environment favorable for plant disease.
Tip: Choose well-structured species and cultivars to minimize pruning needs….most excurrent trees, including conifers, develop good structure with little pruning.Edward F. Gilman – An Illustrated Guide to Pruning
bad and good habits
Well, in botany there are no really good or bad habits! The habits discussed here are plant forms, character of shape and structure, general appearance, or architecture that develops from specific genetic patterns of growth in combination with environmental factors.
Herbaceous (non-woody plants) forms:
Climbing Plants, also called vines, have stems that trail or coil around other plants or structures as they grow upward. Examples include morning glory (Ipomea species) and grape vine (Vitis species).
Clump-Forming Plants have an aggregate of several shoots growing in a bunch from a common base – especially grasses.
Dense Plants grow many small, woody canes or stems very close together in an upright fashion. The majority are shrubs.
Mat-Forming Plants have many stolons (creeping stems) that grow in a trail along soil or water surfaces and spread out to produce a matlike cover. Examples include the grasses Cynodon and Digitaria and Kentucky bluegrass (Poa pratensis).
Mound-Forming Plants grow to form a rounded shape resembling a mound or swollen bump. Examples include barrel cactus (Ferocactus and Echinocactus) and several other species of cactus.
Prostrate Plants stems grow flat on the soil surface or almost touching (hugging) the ground but not trailing. Examples include common mullein (Verbascum thapsus) and some species of juniper.
Scandent Plants have prominent stems in a leaning position. Examples include bearberry (Arctostaphylos uva-ursi) and some bamboos (Bambusa).
Spreading Plants reveal a sprawling type of growth, resulting from profuse lateral branching in mostly woody or succulent stems. Examples include ferns (such as Adiantum) and common juniper (Juniperus communis).
Stemless Plants have no visible stem above ground and are composed mainly of leaves or leaf like structures. Examples include common dandelion (Taxaxacum officinale) and onion (Allium cepa).
Open Plants have upright, woody stems or canes growing in an erect fashion. Their growth resembles a dense habit but has fewer stems and an open, airier structure. Examples include black willow (Salix nigra), smooth alder (Alnus serrulata), and meadowsweet (Spirea).
Erect Plants have one main stem grows in an upright position clearly above ground level. This is common in trees.
Upright tree habit – growing mostly upright or remaining short, these trees have the advantage of fitting into areas with limited horizontal space. They require little pruning and the trunk stays small to medium sized. Disadvantages include: provides limited shade, major stems and branches can develop weak unions with bark inclusions.
Rounded or Vase tree habit – offer abundant shade but although young trees drop fewer branches than pyramidal trees, they are less stable in strong winds than the pyramidal form (Duryea, kampf, and Little, 2007). They can require skilled regular pruning to develop strong structure and branches that eventually drop are often large and leave a wound.
Pyramidal tree habit – what you lose in the moderate shade cast by this form is gained in stron trunk and branch structure that often develops with little or no pruning, stable in wind, and lower branch removal can be performed with unskilled labor leaving a small wound when removed. These lower branches are numerous and and may require pruning for proper spacing along the trunk.
When faced with multiple tree removal in your landscape – dont save trees with poor form because it increases pruning needs in the landscape. Keep those with better form and fewer defects.
buildings, hardscape, and other structures
Consider the mature growth size of your plant in relationship to buildings, sidewalks, and other structures in the garden. Some questions to consider are: will it interfere with overhead power lines? Will the root system interfere with underground water/sewer lines, eventually damage the building foundation or lift the sidewalk? Does the canopy have room to develop into its natural habit without excessive pruning before it reaches eaves or roof surfaces? Will it block a visual vista or window?
Another consideration of overcrowding, mature size and habit in selecting plants is safety. Question if the plant might hinder passage or could it obstruct line of sight? Working in park maintenance and also with residential clients, safety is a factor in the selection, design placement, and pruning of vegetation to create openness, visual security, and prevent crime.
birds of a feather…
Consider your plant selections watering needs and plant like needs together. Irrigation systems are set up to apply the same amount of water to all of the plants in the garden zone so remember; turf watering needs are different than the watering needs of herbaceous perennials, shrubs, and trees.
Know your soil type and light requirements for selected plants. It will lead to disappointment if your sun loving perennial is placed in a shade garden – or a thirsty cultivar in a dry zone. Companion planting is where you place different plants in the same landscape area that share environmental needs, but also provide other benefits such as pest control, pollination, providing habitat for beneficial insects, and making the most of your space with minimum maintenance inputs.
With a little hunting you can find all this information online, in a good general gardening book, or even on the nursery tag. Below is an example from https://www.monrovia.com/plant-catalog/ , a great resource for selecting companion plants for your landscape.
If you live in an area that is prone to forest or wildfires, your plant selection and placement can be critical in saving life and property.
Firescaping is a landscaping technique that involves selecting and placing plants to beautify a property while reducing its wildfire risk. No plant is fire-proof, but some plants have high moisture content, are low growing and lack flammable compounds. They are slow to ignite and produce less heat and flames.
If this is a concern in your area – search firewise (your state) for additional and specific information.
in the zone
What is a Planting Zone? Understanding the USDA planting zone you garden in, can be the difference between landscape success and failure. Selecting appropriate plants that will thrive season after season starts with the map below.
This map is a standard used by gardeners to determine which plants have the ability to survive in their location. It is based on average minimum winter temperatures and divided into 10-degree F zones. Remember that this is just one of the tools used in plant selection for your landscape and specific micro-climates and other factors will be discussed in the Master the Garden series. https://plantsinpower.garden/master-the-garden/
Glossary of Terms
Apex – the tip of a shoot
Apical dominance – the control exerted by the apical portions of the shoot over the outgrowth of the lateral buds. The classical explanations for correlative inhibition have focused on hormone/nutrient hypotheses
Bark inclusion – where bark is included in the union (crotch) of two stems or in the union of a branch and trunk and can weaken the attachment
Bud – a small lateral or terminal protuberance on the stem of a plant that may develop into a flower, leaf, or shoot
Collar – swollen area at the base of a branch where it connects to the trunk
Companion planting – in gardening and agriculture is the planting of different crops in proximity for any of a number of different reasons, including pest control and pollination, providing habitat for beneficial insects, maximizing use of space, and to otherwise increase crop productivity
Crotch angle – the angle formed between the trunk and the main scaffold limb. he best angle is 45 to 60 degrees.
Excurrent – Conically shaped tree with a dominant leader or trunk extending to the top of the tree
Firewise – Originally coined in 1992 by a botanist working with the National Wildland/Urban Interface Fire Program, the term “firewise” describes the state of being knowledgeable and prepared for wildfire in residential or urban settings
Girdling roots – roots growing tangent and embedded into the trunk or into large structural roots causing, or appearing to cause, vascular constriction and inhibition of secondary growth
Head – the part of the tree from which the main scaffold branch originates
Heading – cutting off part of a shoot or limb rather than removing it entirely where it attaches from another branch
Leader – the uppermost portion of a scaffold limb
Plant hardiness zone – USDA Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. The map is based on the average annual minimum winter temperature, divided into 10-degree F zones
Root sucker – a shoot that arises from the root system
Scaffold Branch – a large limb that forms the framework of a tree
Selective pruning – Selective Pruning is a natural way of caring for your plants and trees. It begins by working shrubs and trees from the inside out, by cleaning all of the dead, broken wood, cross branches, and also by controlling the size or direction of the plant
Shearing -Shearing a plant, also called cutting back, is a pruning method that removes large amounts of plant material in one fell swoop. A shearing cut is made anywhere along the length of a plant’s stem at a set height or width, without regard to the structure of the plant
Shoot – One season’s branch growth. the bud scale scars (ring of small ridges) on a branch mark the start of a season’s growth
Spur – a short shoot that bears flower buds and often fruit, either on the end (terminally) or sides (laterally)
Thinning – removing the entire shoot or limb where it originates
Water sprout – a long shoot that grows in an undesirable location on a trunk or a major limb. Vertical water sprouts often arise on the upper side of horizontal limbs
Weak branch union or attachment – may occur at a branch union angle less than 45 degrees, but not always