making the cut: fruit trees

pruning for form, structure, and yield

photo – Brian Barth – modern farmer

Trees have one purpose in life and that is to produce a seed for the next generation, disperse that seed into the world, and to store enough nutrients to survive the winter and manage spring regrowth. For the gardener who grows fruit trees, the purpose is to grow quality fruit in a reasonable quantity, and harvest safely from from healthy trees. Pruning is a management tool that helps align these goals and balances the needs of both tree and gardener.

To correctly train and prune a fruit tree, some basic knowledge of how plants grow and respond to cutting is required, and as a gardener or arborist, every cut should be made with a purpose and the consequences should be understood. When in doubt, do not prune the plant!

structure is the key

To avoid the most common mistakes gardeners make with fruit trees, you have to start at the beginning and it’s all about structure. A fruit tree’s form and structure allows the plant to hold loads of heavy fruit without the branches breaking. This structure is best established when the tree is young, because corrective pruning of mature trees can cause increased stress. Damage like heartwood rot – which will not necessarily kill the tree – can compromise its structural integrity. So starting your tree(s) off right will not only simplify future maintenance, but it will enhance harvest yields and extend the life and productivity of your tree.

photo – arbor care

tree selection and planning

When selecting new trees, look at the structure to avoid problems that may weaken your tree as it matures. Co-dominant leaders and bark inclusion, broken branches and wounds, breaks or other ailments present in young trees that will affect structural integrity as it matures. Remove the wrap or pull it out of the container to check the root health and for signs of girdled roots. Make sure the foliage is free of pests or disease.

After you have made your selection at the nursery and before planting your tree, decide which ‘form’ will work best by considering what type of tree you will be planting, where your tree will grow in the landscape, how much space it will need to mature, and will fruit yields improve if it is left in the natural form rather than manipulated it to grow in an unnatural shape and direction.

photo – Oregon State University Extension

There is one other form that can be considered, Espalier. An agricultural technique used tot grow trees flat on a trellis.

photo – http://www.risingkalefarms.com/

make the cut often and correctly

When pruning there are really only two kinds of cuts, heading and thinning, and you will need to use both when pruning your fruit trees. Without heading cuts the tree will grow too tall and may not create the needed branches to bear fruit. Heading cuts, which are made by removing part of a shoot cutting it 1/4 inch above a lateral bud and leaving a stump, stimulates the growth of buds, or branching, below the cut because apical dominance has been removed. A variant of this cut, used to reduce excess growth that can eventually reduce sunlight, is the bench cut. Bench cut involves cutting back to the lateral shoots and it generally does not stimulate growth of additional branches below the cut like a regular heading cut will.

Thinning cuts are required to prevent shading out of lower interior wood which impedes bud formation. Thinning cuts remove entire shoots, leaving no stub behind, they reduce branch crowding, increase air circulation and sunlight penetration into the lower parts of the tree.  Thinning cuts are also used to establish the main scaffold branches of the tree, by removing unwanted lateral branches during initial tree training.  A tree made less dense by thinning is also easier to treat with pesticide sprays.

Consider branch angles when deciding which branches to thin. In general, angles of 45 to 60 degrees will develop strong branches that can bear the weight of fruit. Branches with narrow angle can be weighted and bent in younger trees if they are still flexible, if they are hardened and inflexible – they are best removed.

photo – Tom Conway Tall Clover Farms

A common mistake made by many gardeners is to not prune enough and often. The fear of making cuts that permanently damage the tree is common, but understanding the basic responses of any plant to pruning and having a clear understanding of the pruning goals makes it easier. With younger trees, the wrong cuts could possibly set the tree back a couple of seasons before it bears fruit.  I have accidently cut seedlings off at the ground and latent buds have grown for me to structure into a new framework. Not that I advocate this process – think of it as a worst case scenario!

node or not to internode!

A brief explanation of nodes and internodes found on every shoot:

When first produced by the apical meristem at the shoot tip, internodes are very short, but will rapidly elongate and cause the shoot and root to lengthen.  This elongation of the shoot and roots by growth of the apical meristem is called primary growth.  Activity resulting in the growth of the vascular cambium located beneath the bark adding wood to the stem, and also the cork cambium, is secondary growth. It thickens and stiffens the bark on the shoots.

All woody plants begin life with primary growth, and begin secondary growth toward the end of the first year. Trees will undergo both primary and secondary growth throughout their life. If a weak branch is cut off half way, the primary growth is stopped, because the apical meristem has been removed – but later with secondary growth will thicken that branch stub. Buds on the stub will eventually start to grow, establishing primary growth.

photo – Arbor Day Foundation

Regular pruning is essential to maintain height and prevent those leggy branches, like water sprouts (long shoots) from shading out your spur shoots. Long and spur shoots differ in their internode lengths and the types of buds they have. All fruit trees, and most plants for that matter, possess long shoots, which have elongated internodes and well spaced leaves. Spurs, which form in the axils of the leaves of long shoots that are two years or older and produced by most fruit trees on last year’s growth, are short and stocky shoots with shortened internodes and can be unbranched or branched. Spur shoots are important because flower buds occur for the most part on these shoots and it is important to identify BEFORE you prune your tree. You do not want to remove or damage these spurs when pruning your tree – because branches at the very edge of your trees canopy are thin and weak and make very poor support for heavy fruit. Spurs, found on much sturdier branches inside your tree’s canopy can support the fruit weight and make harvesting easier and safer.

too much or too little

Pruning…removing and cutting branches from your tree – its as simple and as complex as that! Pruning has drawbacks: it is time-consuming and requires some education and experience; it opens wounds that can lead to disease, and potentially spread disease. If pruning is too severe – fruit yield can be greatly reduced; and increased light penetration, especially in summer, can sunburn bark which can lead to insect attack or disease.  If a gardener is unsure – STOP – and find a guide to pruning.

It is universal knowledge that every cut is a wound to your tree and every wound exposes your tree to disease and other environmental stresses – so it is easy to view pruning with some trepidation and fear of causing harm. I promote conservative pruning habits for mature and veteran trees, differing to the species and environmental conditions, however, with fruit trees a conservative approach in your early pruning maintenance can lead to increased stress on your tree later in its lifespan. Example: if a branch needs removing – but you put it off – it will only increase in size and girth. The cut will be larger or you run the risk of breakage that can damage other limbs also.

A tree that is not properly pruned may possess diseased or damaged wood, or branches that rub against each other, conditions that can potentially shorten the life of the tree.

Additionally an unpruned or lightly pruned tree may shade and inhibit flower production – thus prohibiting the formation of fruiting wood and ultimately fruit production. If a tree is shaded out than fruit production is relegated to the tips of branches where the light is present making harvesting the fruit difficult and risky because you will probably need a ladder. By lowering the tree’s height through proper pruning practices, sunlight can penetrate down to the lower branches which promotes fruit production at the lower height. Sunlight can also be necessary for fruit color development in some species.

photo – l.fowler
balancing act

Knowing how much to prune is important and it requires practice in the art of balancing branch removal for structure and health, and the common problem of gardeners removing way to much. Remember, your tree collects light to produce sugar and it requires foliage to do this. So…. how do you balance the need for removing with the need to collect this light? A seasonal gardener is observant in all the four seasons. I have found one way, not necessarily the most scientific, to make the call on how much to remove from a fruit tree is to note how much sun is penetrating through the canopy when a tree is fully leafed out in summer. More shade than sun…prune more…more sun than shade… prune less. This is a good indicator until you gain a ‘feel’ for the work you are doing and will put the you in the practice of observation and making seasonal notes.

timing the cut

I am often asked when is the best time to prune fruit trees and my answer is anytime! The bulk of your pruning can be done in late winter or early spring, but you can prune any time of the year. If your tree has structural issues or has a contagious disease, address it now and do not wait until spring.

Pruning your fruit tree should be done at a minimum of once per year. Don’t let time of year scare you from making additional pruning cuts as needed.

Russ Metge, Simply Trees
cluster thinning

Growing and maintaining fruit trees requires patience and a willingness to cut and destroy new shoots, flowers, and fruit which is very difficult for many gardeners! Your newly planted fruit trees, depending on species, should not be bearing fruit in the first couple of years and allowing fruit to form in those first two or three years can slow the development of a proper framework for the shoot system.  Remember…. when a tree is at fruit bearing age they often make more buds than desirable – too many buds = too many fruits. Thinning flower clusters can avoid problems with yield including:

  1. Reducing excessive fruit which can lead to smaller fruit size
  2. Reducing the branch load from excessive fruit that can lead to limb breakage
  3. Reduce the complication of biennial bearing, where heavy fruit set one year may inhibit flower bud formation, leading to a small crop the next year
  4. Reduce the need for thinning fruit
photo – pixy.org
fruit thinning
photo – green shutters garden center – rodger Eavis

Often the weight of the fruit exceeds the tree’s ability to support it and you will need to thin the fruit from your tree. Thinning fruit from young trees will encourage good, strong growth assisting in establishment of the tree before bearing the first ‘proper’ crop. It is best to remove all fruit from trees for two years after planting.

When thinning fruitlets on an established tree the crop spread will become more evenly distributed over the tree and easier to harvest when they are not bunched together. When fruit is bunched together it pushes the ‘neighbor’ fruit off the branch and or it is dropped when trying to harvest 4 to 5 fruits in a bunch.

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

Co-dominant leaders – codominant stems is 2 or more main stems (or “leaders”) that are about the same diameter and emerge from the same location on the main trunk. As the tree grows older, the stems remain similar in size without any single one becoming dominant.

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

Heartwood Rot – In trees, heart rot is a fungal disease that causes decay of the wood in the center of the stem or branch. The fungi enters the tree through wounds in the bark and causes decay of the heartwood – as the heartwood softens, the tree becomes structurally weaker and prone to breakage.

Internode – a part of a plant stem between two of the nodes from which leaves emerge

Leader – the uppermost portion of a scaffold limb

Node – part of the plant stem where the flowers, branches, and leaves first start to grow. Nodes can hold several leaves and buds that have the capacity of growing and spreading into branches. In some plants, the nodes can additionally produce adventitious roots

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

Primary Growth –  in stems and roots, is a result of rapidly dividing cells in the apical meristems at the shoot tip. Subsequent cell elongation then leads to primary growth

Root sucker – a shoot that arises from the root system

Scaffold Branch – a large limb that forms the framework of a tree

Secondary Growth –  the growth that results from cell division in the cambia or lateral meristems and that causes the stems and roots to thicken

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

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