pruning 101

Pruning 101

Intro

Pruning and training plants is one of the most satisfying gardening activities. It is amongst the most practical activities we need to undertake. Pruning though a puzzling operation to many, is no more complex than other garden practices, requiring only reasonable knowledge and some common sense.

Most plants need little pruning if left to their own devices, however we often ask a lot of our plants, and need to guide them to our agendas. A plant has it’s own ideas what height and form it should be, when we prune them we interfere with their genetically pre determined path.
Most woody plants have shoots ending in a terminal or apical bud, below which the other buds are arranged as per the pattern for the species. The apical bud regulates the buds below it by producing a chemical. If this bud is removed the growth retarding chemical supply is interrupted, and the affected buds now break into growth. New growth is the result until a new bud exerts apical dominance. It is this mechanism that we channel new growth into a desired result.
When we prune can also induce or inhibit new growth. To control our result we must be aware when to prune. Dormant pruning stimulates new growth, whereas summer inhibits it.
It is critical to know the plants growth habits, especially in the case of fruiting or flowering plants, and whether they bloom on old or new growth. If you dormant prune early spring flowering shrubs you will lose a seasons flowers. Spring flowering plants are blooming on last seasons matured wood or old growth. Old growth can be renewed and kept vigorous by pruning out directly after flowering. The old adage if it blooms before June don’t prune, is an easy way to remember this rule.

Pruning to keep a plant small is a crude method of control that often doesn’t work well. It is better to choose the right size plant than to work against nature. Many trees and shrubs need less pruning, as they become mature. When you prune young branches they heal quickly, so it should be a well considered decision to out large branches. The most intensive pruning is often carried out on young trees to create an optimal framework, and once that is established it is a matter of light maintenance. Forcing a tree into a flush of tender unhardened growth before winter can result in frost damages.

Ornamentals

Multi stemmed shrubs that exhibit colorful new growth, or juvenile foliage, are best cut back hard each spring. Examples of these are red twigged dogwoods, and eucalyptus.
Shrubs that flower on current seasons, or new growth wood like Hydrangea paniculata benefits from a hard pruning in spring.
Many ornamentals like the magnolia need little pruning once they are mature, except to remove dead or damaged growth.

Roses
Roses have a number of main forms and habits that are pruned differently. Roses are usually pruned after all danger of frost has passed, “when the Forsythia blooms” is a helpful indicator to make note of. It is however a good idea to tidy up large plants that may become damaged by winter wind whipping.

Hybrid teas

Hybrid perpetual

Floribundas

Polyanthus

Miniatures

Species, and Shrubs
(Groups 1, 2, &3)

Climbers, and Ramblers
(Groups 1,2,3 &4)

Standards

Trees

Trees can generally be divided into two main types, those with a strong central leader, and those with a pattern of branches forming a crown. The first 5 to 10 years emphasis are placed on establishing a strong, durable balanced framework. In most cases this consists of the removal of badly placed shoots and branches, or the maintenance of a strong leader. The angle at which a branch grows from the trunk makes it a strong or weak branch. Weak branches can be removed or sometimes trained to a better angle. In the case of trees that form a crown it is best to establish a framework off of a single dominant leader rather two co leaders. The angle between co leaders can be weak. Weak angles can form excess bark in the crotch that leads to rot or disease.

Pruning cuts

The pruning cut, as with any injury is a point of entry for disease in the tree. Small cuts, on young trees heal quickly, whereas large cuts on mature trees heal slowly. The angle of the cut is also crucial. The best indicator of pruning cut angle is the branch bark ridge and the branch collar. The collar is an area or ridge of bark apparent at the base of the branch where it joins the tree. The branch bark ridge is visible on the trunk and often follows the angle of the branch as it intersects off the tree. To remove a branch with the minimum risk of decay make the cut close to the trunk, but angled so that it is outside the branch bark ridge, and the branch collar.

When to Prune

Deciduous trees are usually pruned in the dormant season and broadleaf evergreens as they are coming into growth in the spring. Trees, which bleed heavily, should be pruned in late winter or early spring so as to be closer to spring and healing. Conifers are also best pruned late winter early spring.

Suckers
Suckers are shoots that grow from the roots of trees which are prone to suckering such as Sumac, and Lilacs. They can also appear on trees that have been grafted with a rootstock prone to suckering. Suckers should be removed as soon as possible when they are in full leaf. It is good where possible to expose the root and cut them back to that junction. Suckers that appear below a graft can become dominant and take over the desirable grafted growth of the tree.

Epicormic shoots

Trees that are wounded or stressed often produce epicormic shoots or water sprouts. It is common to find this growth around large flush cut pruning injuries. These weak shoots should be pruned out annually.

Feathered Trees

Many deciduous trees naturally form a strong central leader, with lateral branches growing more or less symmetrically from the trunk. They are easily trained and require very little pruning. The main concerns to watch for with this tree type are strong growth from the base; the development of a forked or double leader, weak angled, or crowded laterals. In the case of a double leader chose the weaker and prune it out. Remove branches weak angled branches, or retain them and try and correct the angle if cutting it out seriously effects the trees shape. It is usually best to remove bottom growth, unless you are encouraging a multi-stemmed tree. Broad-leaved evergreens such as holly, and some conifers have a feathered tree form.

Standard Trees

The central-leader standard
Standard trees are trees, which have a clear trunk. This often is a feathered tree with the laterals removed to a height of approximately 5-7 feet. The laterals shouldn’t be removed too soon as they support the tree growth, rather the first few years. The normal practice is once the tree is of sufficient size, to reduce the laterals size in half the first year, and back to the main stem in late fall, or early winter.

The branched-head standard
The first years of training are the same as the central leader tree. In the mid to late fall cut the central leader back to a strong bud or lateral about 1.5 –2 feet above the height the lowest branch is wanted. Usually 3 to 5 well-spaced laterals are retained to develop the framework of the head. With these trees all growths on the clear stem should be rubbed out (thumb pruned) as soon as they appear. Established branched-heads require thinning of congested growth to maintain an open center. Any growths such as upright shoots, that destroys the symmetry of the laterals should be cut back to a well placed lateral. Whole branches can be cut back to the main trunk if need be.

Weeping Trees

Many weeping trees are top-worked branched-head standards. Weeping willows and a few weeping trees are grown on their own roots. With these trees retain the central leader as long as possible. Many weeping trees are grafted onto a standard trunk and rootstock, so any growth below the graft must be removed. The head of a weeping tree often forms a dense overlay of pendulous branches. To keep the head open train the top most lateral 1-1.5 feet up a cane as a continuation of the main stem, and allow the laterals growing from it to form an upper tier of branches.


The Care of Established Trees

Established trees often require very little pruning over many years. Tree pruning trees can be hazardous, heights, size, equipment and power lines need to be considered, and is often best left to a professional.

Crown lifting

Crown lifting is the removal of the lower branches of a tree; it is often done to let light in underneath the tree. Crown lifting is best carried out while the tree is young, but often it is often relatively straightforward. In the case of mature trees, where large wounds will be made it is best to remove limbs over two or three years. Removing a large amount of a trees lower foliage can be harmful to it. Aim to maintain a balanced shape, even if the branches you want to remove only fall on one side.

Crown reduction

Crown reduction reduces the overall height and spread of the tree crown by cutting back selected branches to lower limbs or laterals. It usually needs to be done every 4 years or so. Not all trees respond well to this treatment. Birch and poplars are prone to rot, and Beech should not be reduced by more than 10%. As a rule young trees with lighter branches respond better. It is best to initiate crown reduction before a tree reaches mature heights.

Crown thinning

Crown thinning is a skilled technique of pruning established trees. It does not reduce the overall size of the tree but usually is done to allow greater light and air circulation. It is often performed on trees that have produces excessive weak growth. Trees with weak growth, and root structures are more susceptible to wind damage. Crown thinning is also sometimes done to reduce the amount of heavy shade cast by a tree. As a rule remove the crossed, weak, dead, and dying, and selected branches for balance, retaining at least two thirds of the original growth.

Lopping and Topping

Lopping and Topping are crude methods of reducing a tree size, and should not be recommended as a method of pruning. The large wounds it creates often leads to rot, and the decline of the tree. These trees are also prone to epicormic growth, and weak branching that makes them vulnerable to wind damage.

Shrubs

Shrubs often need minimal pruning beyond the three D’s

Deciduous shrubs

Group 1 (little pruning)
The deciduous species and hybrids of Magnolias are among a large number of shrubs, which require little pruning. Remove any weak or crossed branches in spring. Watch that the framework doesn’t become crowded, and remove dead or diseased growth. The growth pattern of weeping Japanese maples is naturally intricate and some crossed branches are perfectly fine.

Group 2 (flowers on last year’s growth)
If left not pruned this group tends to make twiggy excessive growth, resulting in reduced flowering. Lilacs become tall and only flower on the tops for example. The annual removal of old wood encourages the development of new growth from the shoots down low on the shrub and keeps the plant compact and vigorous. It is essential to carry out this pruning immediately after flowering. Formative pruning involves pruning to a balanced framework, and heading back branches no more than 6 inches to a strong bud or pair of buds. For established plants reduce the growth that has flowered to new growth further down the stem. You can renew a woody crowded shrub by removing a quarter to third of the oldest or damaged branches to the ground.
Variants
Kerria, broom, and hydrangea are some of the variants in this group. Kerria benefits from having some of its shoots pruned to ground level after flowering. Although Hydrangeas are late flowering they bloom on last years growth. Hydrangeas prefer not to have a drastic pruning in spring. Mature Hydrangeas can have some of their oldest growth removed, and last years growth reduced to a pair of fat healthy buds. The next year’s growth will come from the base of the shrub.

Group 3 (deciduous bearing on current season’s growth)
This group of plants is valuable for late summer or fall color. It blooms on current growth so benefits from hard pruning in early spring to promote vigorous growth. If left not pruned these plants tend to be twiggy and leggy, blooming at the ends of their topmost branches. This group includes Hydrangea paniculata, Buddlia, and Perovskia. Many of these plants can be pruned down to a low framework near the ground.

Group 4 (shrubs pruned hard in early spring for decorative bark or foliage)
For these shrubs grown mainly for their bark or foliage interest, a hard pruning and generous feeding provide a vigorous crop of new growth. Eucalyptus, Cornus, Rubus, Cotinus shrubs fall into this group.

Evergreen Shrubs

Group 1 (minimal pruning)
Broadleaf evergreens such as Camelia need very little pruning, as with all shrubs remove the 3 D’s and perhaps a reduction of a leader of out of balance branch is all that is required. Dwarf conifers fall into this group; healthy specimens don’t need any pruning. Pines can be made more compact by pinching out the candles or new growth in half. Die back should be removed, as it is unlikely to generate any new growth.

Group 2 (Evergreen shrubs that are hard pruned to keep compact)
Some evergreen shrubs tend to deteriorate quickly, left to their own devices. Lavender, Santolina, Hypericum, Mahonia, and the summer and fall flowering Heathers all appreciate a mid-spring trim of old flower spikes from the previous season. Lavenders don’t flower well on woody older growth so they do best with an annual trim to keep them in mid spring just as new growth is forming.

Renovating Shrubs
Deciduous
Some shrubs can be renovated with drastic pruning. Lilacs are good candidates for this treatment. A well fed and watered specimen will make a better recovery, pampering will go along way. The aim is to cut the tree to 1-2 feet in late fall, early winter. In mid fall of the same year thin the new growth to 2-3 shoots per main stem leaving the best placed and strongest. Other shrubs that tolerate this sort of renovation are Deutzia, and Philadelphus.

Evergreen
Rhododendrons and Laurels may be renovated this way, although Rhododendrons may not respond as well. Cut back the rhododendron immediately after flowering. Laurels need to wait till early summer to avoid risk of bacterial cancer.

Climbers, and wall shrubs

Climbers and wall shrubs present two extremes of pruning and training. Some climbers need no care, whereas others will need regular attention to keep from becoming a neglected looking mess. Climbers climb or cling in a number of different ways, true climbers cling with aerial roots or sucker pads. Another group of climbers have twining stems, leaf stalks, and tendrils. Roses use there thorns to hook into other plants or surfaces, and others simply rely on rapid growth. Shrubs which grow against walls such as Pyracanths, Berberis, and Chaenomeles don’t actually climb at all. In general we can follow the “if it blooms before june, don’t prune” and other the shrub rules already mentioned
clematis.
Clematis are generally divided into 3 pruning groups A, B, and C. In the first year of planting all types should be cut back to a couple of sets of healthy buds.
Group 1 Clematis are species and hybrids which flower in summer or fall on current years growth. Prune this group when dormant prune each stem down to a strong pair of buds.
Group 2 Clematis flower in early spring on last years growth and are best pruned right after flowering and can tolerate a hard pruning if well fed and watered.
Clematis group 3 flower on old wood and subsequently on new growth in the same season. This group can be pruned like group one if it is out of control. A system of renewal pruning where you prune ¼ of the old stems out within a foot of the ground immeadiatly after flowering in mid summer.

Wisteria
Wisterias are most commonly trained onto pergolas, but may be trained as an espalier, standard, or shrub. The pruning is the same, to encourage the formation of flowering spurs. Prune the laterals in two stages in mid summer to about 6 “, then when dormant down to 2-3 buds.

Forming an espalier
1st year establish a leader, cut back the main stem, and remove all other lateral growths

2nd year train the top most leader as a new extention leader, and the two below as the first laterals, initially tying them at 45 degree angles. In winter lower the first arms to horizontal, and reduce by about a third and shorten the leader shorten the leader to 2 ½-3 feet above laterals.

3rd year train the topmost leader as a new extention leader, and the two laterals below it as laterals , intialy tied at 45 degrees. When dormant lower the 2nd set of laterals to horizontal and shorten the leader to 2 ½-3 feet above bottom set of laterals. Repeat this process until the required number of laterals is produced.

Spur prune back unwanted growth to within 6” of the laterals in mid summer, and again in mid winter to 2-3 buds.

Hedges
When pruning an established hedge the top cut is first applied to make it level. Hedging shears laying flat against the surface of the hedge. A guideline may be required if the hedges surface is overgrown. The batter of the hedge is the angle of the sides, and it should be at an angle of 15 to 25 degrees. This allows for sunlight to reach the bottom. Hedges should be trimmed when you would prune a shrub of the same variety. Many hedging plants need only one annual cut if it is carried out in late summer. Fast growing hedges may need several cuts in a season. Most deciduous hedge plants are best pruned in late summer through fall.