What is pruning plants?

What Is Rejuvenation Pruning: Tips For Hard Pruning Plants

Most shrubs need annual pruning to keep them from overgrowing their surroundings and developing thick, unproductive branches. Once a shrub is overgrown, the usual thinning and trimming methods won’t correct the problem. Rejuvenation pruning is drastic, but if done properly, the result is like replacing the old shrub with a new one.

What is Rejuvenation Pruning?

Rejuvenation pruning is the removal of old, overgrown limbs so that the plant can grow new, vigorous branches in their place. Plants that require rejuvenation can be hard pruned or pruned gradually.

Hard pruning involves cutting the shrub off to a height of 6 to 12 inches above the ground and allowing it to regrow. The disadvantages of this type of pruning are that not all shrubs tolerate drastic cutting, and until the plant regrows you are left with an unsightly stub. The advantage of hard pruning is that the shrub rejuvenates quickly.

Gradual rejuvenation allows you to remove old branches over a period of three years. This technique is called renewal pruning. Although it

is slower than hard pruning, shrubs that are rejuvenated over a period of time look better in the landscape as they regrow. This method is particularly well-suited to caning shrubs.

How to Hard Prune Plants

If the stems you are going to cut are less than 1 3/4 inches in diameter, use heavy long-handled pruners for the job. The length of the handles gives you more leverage and lets you make clean cuts. Use a pruning saw for thicker stems.

Hard prune in spring before the buds begin to open. Cut the main stems back to 6 to 12 inches from the ground and cut back any side branches below the first cuts. The best place to cut is 1/4 inch above an outward facing bud or node. Cut at an angle so that the highest part of the cut is just above the bud.

Plants that require rejuvenation and respond well to hard pruning include:

  • Dogwood
  • Spirea
  • Potentilla
  • Honeysuckle
  • Hydrangea
  • Lilac
  • Forsythia
  • Weigela

Pruning Plants Gradually

In early spring, remove 1/3 of the canes, cutting them all the way to the ground or main trunk. Cut side branches back to the main stem. In the second year, cut 1/2 of the remaining old wood, and remove all remaining old wood the third year. As you thin the shrub and the sun begins to penetrate to the center, new growth replaces the branches you have removed.

This method isn’t appropriate for all shrubs. It works best with shrubs that consist of several stems arising directly from the ground. Shrubs with tree-like growth consisting of one main stem with several side branches are difficult to renew by this method. When shrubs have been grafted onto rootstock, the new branches come from the root stock.

Plants that respond well to gradual rejuvenation pruning include:

  • Purple sand cherry
  • Cotoneaster
  • Burning bush
  • Viburnum
  • Witch hazel

Pruning shrubs

Why prune shrubs

Shrubs create the structure in a garden so it’s important to keep them in good condition with regular pruning. This will improve a plant’s shape and encourage flowers and fruits.

What to do

How and where to cut

  • Pruning cuts are essentially wounds to the plant where disease could enter so use sharp, clean tools and make clean cuts without leaving snags. Cut close to buds, but not into them, and always above.

Pruning young shrubs

  • Early pruning helps establish a shapely shrub with vigorous, balanced growth.
  • Most evergreen shrubs do not need thinning or formative pruning. However all shrubs benefit from shortening any excessively long shoots and cutting out weak or damaged growth.
  • Deciduous shrubs are more likely to need pruning into shape; this is known as formative pruning. Young shrubs often grow lots of shoots so you will have to thin them early on.
  • Correct lopsided growth by lightly pruning longer shoots and hard pruning weak stems.

Rejuvenating old shrubs

  • Shrubs such as forsythia and buddleja can soon accumulate masses of old, dead wood in the centre if they are not pruned regularly.
  • The best way to rejuvenate these plants is to cut them back during the dormant season.
  • First cut out dead, diseased and crossing stems, and then thin the number of remaining stems by half.
  • Shrubs that respond to severe pruning, such as ribes and philadelphus, may be cut almost to ground level to re-establish a framework of new shoots. If the shrub is old and it’s hard to predict a successful revival, take cuttings just in case.

Pruning shrubs in pots

  • Once a container shrub reaches maturity it is usually best repotted annually in spring, or every other year, using the same or similar sized container.
  • If you find the plant is very pot-bound, this is a good time to lightly prune the roots.
  • Prune about one-third of the thicker non-fibrous roots back to the intact rootball, but avoid damaging the fibrous feeder roots.
  • Repot in fresh compost and finish by pruning the top growth by about one-third to balance the root loss.

Coppicing and pollarding shrubs

  • Shrubs grown for their colourful stems or foliage, such as dogwood, need to be cut down every spring to 4-5 buds to encourage new growth.
  • This is known as coppicing. If you want to keep a framework of older stems, cut down one-third of stems.
  • A similar technique is called pollarding where stems are cut back to the same point a single stem or framework of stems. This is often seen on London plane trees and can be used on eucalyptus. After pruning, make sure you feed and mulch the plant.

Pruning shrubs in autumn

  • After a summer’s vigorous growth, it is a good idea to give your shrubs a light prune in the autumn to keep them in shape.
  • Once deciduous shrubs lose their leaves, it is easy to see the plants’ overall shape and decide what needs to be cut back.

Watch video

In this video Colin Crosby, the superintendent of woody ornamentals at RHS Wisley, prunes dogwoods and willows in spring to encourage new growth.

Plant-by-plant deciduous pruning tips

Buddleja

  • In mid-spring cut back last year’s shoots to one or two pairs of buds from the base.
  • Remove some older branches if the bush is overcrowded.

Cotinus

  • Hard prune to ground level in late winter to stimulate next year’s foliage, or remove one-third of stems in mid-spring for a display of fine young foliage and attractive flowers.

Cotoneaster

  • If grown as a dwarf hedge, clip in late-winter and mid-summer although you will get fewer berries.

Cytisus

  • Prune after flowering, shortening all young green growth by up to two-thirds, but avoid cutting back into the old wood.

Forsythia

  • After flowers have faded, thin out one-third of the branches to improve shape and next year’s flower quality.

Pyracantha

  • Between late winter and mid-spring, trim wall-trained bushes to shape, cut out weak growth and shorten new shoots to encourage branching.
  • In late summer, cut back new growth on fruit-bearing stems.

Lilac

  • Cut back shoots after flowering to a pair of leaves below the flower-head.
  • In winter, prune weak branches back to their base, remove suckers and thin out older branches.

Renewal pruning of currants
Currants produce fruit on spurs that emerge from 2- and 3-year old wood. After that, those limbs are far less productive. Use the following pruning schedule on currants:

  • Year One – remove all but up to three stems at ground level
  • Year Two – remove all but two or three of the previous season’s new stems
  • Year Three – repeat Year Two
  • Year Four and ever after – remove any stems that are more than 3 years old and trim back any low-hanging branches

Renewal pruning of fruit trees
Fruit and nut trees produce fruit on spurs and on twig tips. Some species only produce fruit on new spurs, while others can use the same spurs for several years. For example, figs, grapes, persimmon, and quince produce fruit on new shoots and one-year old wood. Pears, walnuts, and apples, on the other hand can produce fruit on the same spurs for several years. UC Davis offers a chart offruiting wood characteristicsthat can help you decide what to remove and what to leave for another year. Did you know that large, unproductive branches are called bulls? I didn’t either.
Renewal pruning of raspberries and blackberries
Some varieties of raspberry and blackberry produce fruit on primocanes. These are fall-bearing varieties that produce the best fruit on first-year canes. While leaving them in place will provide some fruit the following spring, the quality and quantity are usually poor. For these berries, it is better to cut the canes back to ground level in late autumn. This gives the plant time to pull carbohydrates from the leaves down into the crown and root system. These nutrients will be used to grow new canes in spring. Summer-bearing floricanes produce fruit on buds from second-year canes, so removing them at the end of year one would be problematic.
Rejuvenation pruning
Some trees and shrubs can become so out of control that they risk falling over, severe disease infestation, or they simply look awful. In some (but not all) of these cases, rejuvenation pruning can be used to give them a new start on life. These plants are cut to ground level and allowed to start over from an established root system. Before you try this method, be sure to research the plant to make sure this is an appropriate choice. Cutting back some plants in this way will kill them.

Whole tree pruning
Traditionally, trees that produce fruit in new growth, such as cherries, are pruned by removing selective branches. Another method being studied is whole tree pruning, in which all the major limbs are removed each winter, leaving only 12 to 18 inch nubs. This method is not for the faint of heart, but it is gaining popularity among commercial growers.
Don’t be afraid to prune your trees and shrubs. It is an excellent way to help your plants to stay healthy and productive. As you move around under the canopy or peaking into the center of your shrub, you may even discover a new pest or disease before it gets out of hand!

renewal pruning

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While many tasks in the garden provide a healthy sense of accomplishment, rejuvenating an overgrown shrub makes you feel like an artist. Transforming a rangy, ugly mock orange or dogwood into a thing of beauty is easier than you think.

Rejuvenating a multistemmed shrub involves removing one-fifth to one-third of the oldest and largest stems at ground level, says Gary Watson, plant physiologist at the Morton Arboretum. He believes that most shrubs benefit from regular renewal or rejuvenation pruning.

Cutting the larger stems encourages vigorous growth from the ground, making the shrub full from the bottom up, Watson says. Selective pruning also improves the shrub’s flowering capacity by allowing more light to reach the interior of the plant.

Old shrubs that haven’t been regularly pruned may need complete rejuvenation, a three-year process, while young plants will only require light renewal pruning each year.

Tools and tips

One of the most important aspects of renewal pruning is using the right tools, says Michael Schneider, a horticulturist in Kenosha. A pair of good pruning shears and a sharp pruning saw are as important as the process. Jagged cuts and frustration from making a tool do something not intended can ruin the outcome.

Although overgrown shrubs detract from a landscape, it’s also important to consider how the landscape will look while waiting the two or three years it takes a plant to recover from severe pruning. Both Watson and Schneider warn against renewal pruning when a shrub is unhealthy or stressed. Shrubs may be particularly stressed with the very dry early summer we’ve had, so spend the summer bringing the shrub back to vigor and then prune in late fall.

Renewal pruning tips from Schneider include:

First, assess a shrub’s shape and growth tendencies. Since you have to work with what is there, study the shrub carefully. Is it upright or spreading or more of the branches come from the ground or from forks above the ground?

Begin pruning by removing any diseased or damaged branches. Next, select up to one-third of the oldest stems and cut them at ground level with long-handled loppers or a pruning saw. Schneider suggests that “stems be carefully removed from all sides of the shrub to keep it somewhat symmetrical.”

Remember to periodically step back and look at the shape of the entire plant as you are pruning. With an old shrub, it’s tempting to jump in and start cutting, but caution and patience will produce a better plant. It is important not to remove any more than one-third of the shrub at a time in order to leave enough leaf surface to provide food for the plant.

After removing the large stems, prune out any crossing branches, open the crown to more sunlight by thinning side branches and shorten other stems to produce a pleasing shape. Step back one last time and do any final shaping.

The job is finished for this year. Next year, follow the same process, removing another third of the old branches and continuing to shape the plant. Remove the remainder of the old stems in the third year, finishing the renewal. From this point on, annually remove only one-fourth to one-fifth of the oldest stems, keeping the plant well-shaped and blooming.

Renewal and recovery

To illustrate how renewal pruning can improve a plant`s health, Watson relates the story of an established lilac that wilted every time it went without water for three days. Apparently, the old stems were not taking up enough water to sustain the plant.

He took out all the woody canes over two years and the plant recovered beautifully, losing its drought-sensitivity in the process.

Schneider said he believes that healthy old lilacs with few stems should be regarded as small trees rather than shrubs. “Rather than trying to rejuvenate it by completely removing these stems, prune up the lower branches to reveal its attractive bark.”

Schneider believes that if a shrub is so ugly the only alternative seems to be removal, it’s worth cutting it back to the ground to see what happens. Plants such as honeysuckle, some spirea, forsythia and privet will recover well when cut entirely to the ground because they re-sprout vigorously. Shrubs that don’t respond well can always be removed.

Although most renewal pruning can be done in late fall, late winter and early spring, wait to prune shrubs that bloom in spring until after they’ve finished blooming. This allows you to enjoy the blossoms instead of losing them to pruning.

Pruning a shrub is a lot like cleaning out a closet. It makes everything tidy, removes the old “stuff” and gives a great sense of satisfaction.

TO PRUNE OR NOT TO PRUNE

Here are lists of shrubs that respond well and ones that don’t respond well to renewal pruning, and some additional tips:

How they respond

Shrubs that respond well to renewal pruning: Forsythia, honeysuckle, lilac, mock orange, potentilla, privet, redtwig and yellowtwig dogwood, shrub roses, spirea, viburnum.

Shrubs that don’t respond well to renewal pruning: Boxwood, burning bush, junipers and yews, rhododendron and azalea.

When to prune

Prune in summer after blooming (plants form flower buds in late summer of previous year): Flowering quince, honeysuckle, lilac, mock orange, redtwig dogwood, spring-blooming spirea, some kinds of viburnum, weigela.

Prune in early spring before growth begins (plants bloom on new wood): hypericum, privet, potentilla, rose, summer-blooming spirea.

Hard pruning is a pruning technique that removes quite a lot of wood. It is also known as three-budded pruning since it involves cutting apple and pear trees back to the third bud on fruit-bearing branches and is recommended for artificially structured apple and pear trees such as cordons, espaliers and fans.

© iStockphoto/Thinkstock

You need to take account of how vigorous the tree is before you prune it. If last year’s growth was less than 20 inches (50 cm), then it is not a particularly vigorous tree and will benefit from hard pruning. You should prune in winter when the tree is dormant and cut back to three buds on each spur bearer, a lateral branch that grows on a framework or primary branch.

If last year’s growth was more than 20 inches (50 cm), then you are dealing with a vigorous tree that will be difficult to control with hard pruning. Bend the rules of three-budded pruning and don’t cut back as hard, leaving four, five or six buds on each spur bearer.

If trees have been neglected, the spur bearers are often multiple and complicated. Don’t have any qualms about simplifying them by keeping only those closest to the framework branches.

  • Hedge shears (large flat, scissors style shears) are designed to shear light new growth. Ideal for light shaping, trimming and heading.

  • Electric hedge trimmers are convenient for bigger jobs, where a manual hedge shear may get tiring. Cordless trimmers with rechargeable batteries make the job much easier, especially when the trimming job is a sizable distance from power.

The biggest confusion for gardeners even when they know why they need to prune is how to go about it, and how seriously to prune or shear. For the most part you should do what seems to make sense based on the needs of the shrub and your objective. Just don’t be afraid of doing it, pruning will nearly always do good things for your shrub. If you are concerned about butchering or killing a badly overgrown or out of control shrub, don’t be. There is a proper way to prune for that problem too.

  • The first step in every pruning project is to remove every dead, diseased, broken, damaged, weak and wayward branch. This will reduce the possibility of disease and insects entering the plant. Make sure your tools are sharp and clean. A pruner that has been in contact with disease will pass the disease to every plant you prune. Clean with a solution of 1 part alcohol, 9 parts water. And a dull blade will crush rather that cut the branches, leaving the branch damaged. Use your pruning shears, or loppers if the branches are large, to completely remove dead branches. Do not leave stubby branches, cut as close to the branch collar (the swelling where the branch joins the trunk) as possible without cutting the collar. This will promote quick healing. There is a chemical zone in the collar that inhibits the spread of decay, so you also do not need a tree wound dressing. If the branch is diseased, damaged or broken you can just cut back to healthy branch, which should not be black or discolored. If you have not removed back to healthy wood, the disease or decay will spread to the collar anyway, and the entire branch will later need to be removed. Make cuts just above an outward facing bud so that a new branch will grow out, rather than inward and crossing with other interior branches.

  • The preferred method of pruning is thinning, which is removing selected branches back to a side branch or the main trunk. It opens up the interior of the shrub to receive light, encouraging interior growth. Thinning will reduce the size of the shrub and result in fuller growth. It also helps to maintain the natural form of the shrub.

  • Heading is the removal of the end portions of twig branches randomly. Not to be confused with shearing, this is generally accomplished with a pruner to remove certain long, tall, or wayward branches. It is sometimes done to reduce the overall size of the bush, with the intention of maintaining its’ natural form, or moderately controlling its’ shape. Heading will stimulate growth of new shoots and encourage it to become more dense. Before making a cut, determine if a new shoot should be encouraged to grow outward or inward. Then cut just above an inward facing bud to encourage an inward branch, or an outward facing bud to encourage an outward branch. Do consider the natural form and how you can encourage select growth that will maintain that form.

  • Shearing (often called clipping) is removal of the growing points (that is just the tips of the branches) at an even level using a hedge shears or electric hedge trimmer. The shrub responds by increasing the growing points. Each branch will generally divide to form a dense top layer of growth. The shearing method is used to form hedges or topiary. It has become common to “shear” for general shaping of shrubs and informal hedges. Repeated pruning by this method will cause foliage growth to be concentrated on the outside of the the shrub, preventing light from entering the interior. Eventually the shrub will become completely bare on the interior. Radical renewal pruning will be necessary. Thinning and heading instead will maintain a healthy shrub much longer.

  • Pinching, in the same way we encourage an annual or perennial to grow lateral shoots to produce a dense plant, will also produce a denser shrub. Pinch the growing point between your thumb and forefinger and snap it off. Buds below the point will break dormancy and produce lateral shoots. This method can also be used to slow growth in a part of the plant, since the pinch also delays growth for a couple of weeks.

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