How To Prune Shrubs
What did shrubs do before man came along with his pruners, shears and hedge trimmers? They grew naturally of course - and where we might live now in suburbia probably looked like a jungle! And in jungles, there are snakes and other critters - which some find scary - crawling all over the place. But that was then and this is now.
Though not all shrubs require pruning, many do - particularly if we want them growing in our landscape. And pruning can be effective to form certain shapes, sponsor a new flush of blooms, and to rejuvinate an old, scraggly looking shrub. So there are many benefits to pruning shrubs.
Some gardeners find pruning to be one of the most therapeutic gardening tasks, not only for their plants, but for their own mind and well-being. It's easy to forget about the worries of the world when focused intently on pruning a plant.
Others like to avoid pruning altogether, or keep it to a bare minumum. Either they are afraid to make the wrong cuts, or they simply don't have time to do it - or don't want to spend the money to do it. These gardeners will typically look for the "low-maintence" shrubs when shopping at the nursery.
If you have some shrubs in your yard that you think need pruning, there are a few basic things you'll need.
Pruning Tools
First and foremost, be sure to have the right tools on hand. Sharp pruning shears are a must for every gardener and homeowner - the higher the quality, the easier it will be and the longer they will last. You can also have secateurs, lopping shears, pruning saws and other such tools, but the basic shears are essential. If you have a hedge, a set of power shears will make life much easier, but is not essential. Make sure to keep your shears sharp, and prep them for winter storage each fall with a light application of oil.
Things You Should Know Before Pruning a Shrub
Understanding the natural "habit" or shape of shrubs will help you determine how to prune them. All shoots grow outward from their tips. Whenever tips are removed, lower buds are stimulated to grow. Buds are located at nodes, where leaves are attached to twigs and branches. Each node produces from one to three buds, depending on shrub species.
Shrubs have mounding, cane, or tree-like growth habits. Those with mounding habits, such as evergreen azalea and spirea, generally have soft, flexible stems, small leaves, and are often used in mass plantings.
Shrubs with cane habits include forsythia and nandina. These shrubs spread by sending up erect new branches, called canes, from their base.
Tree-like shrubs have woodier, finely divided branches. Loropetalum, ligustrum, rhododendron and wax myrtle are just a few examples of shrubs with tree-like habits. Thoough these will produce branches and foliage from the base of the plant, many gardeners like to limb them up into small, attractive trees that can be useful in the landscape as "tree-form specimens."
When pruning, you should always trim a branch back to just above one or more healthy leaf buds, no more than about half an inch above. Don't leave stubs; these will invariably die and can become havens for insect pests and disease. Also note that some evergreens like pines and spruce only have terminal buds, and should be treated a little differently. These are best pruned as the new growth is vigorously developing in early summer; cut back a portion of the newer growth (often called "candle"") to control their shape.
When To Prune A Shrub
It is important to know when to prune your shrubs. Some of the techniques described below can only be performed at certain times of the year, and you are advised to follow the instructions faithfully. With other techniques, the shrubs can be pruned at almost any time, although there may be consequences. Specifically, there are two primary considerations when it comes to the right time to prune shrubs.
The first has to do with the time frame in which a particular shrub blooms. Obviously, if you’re undertaking a brutal rejuvenation pruning, you’re not going to be expecting much in the way of a flowering performance that year, or even for a year or two down the road. But for an annual trimming or pruning to shape, it becomes very important to know when a shrub blooms in order to ensure that it will still perform as intended that season.
The rules are actually quite simple. You should only prune summer-blooming shrubs in early spring, and prune spring-blooming shrubs immediately after they have bloomed. With spring bloomers, an late winter, or early spring pruning before flowering will actually remove the flower buds and could severely inhibit any flowering performance, while waiting too late after they have bloomed could remove the newly formed flower buds for the next season. The key with summer bloomers is to not prune them after they have flowered, as this will probably be too late in the season for the vigorous new growth that will ensue to harden off before Winter to any safe degree.
Shrubs which bloom on new growth that emerges from wood of the previous season, such as viburnum and weigelas are best treated as early spring bloomers and only pruned immediately after flowering.
In northern regions, it is best not to prune any shrub after July. In southern region after August. Late pruning stimulates vigorous new growth in most shrubs, and the last thing you want is tender new growth going into winter. Allow plants, especially those one;s you keep trimmed into hedges, to harden off for the Winter before pruning.
Types of Pruning Cuts
It would be impossible to provide instructions here on all the various pruning techiques there are for all the various types of shrubs. And some shrubs, such as Hydrangeas, require specific pruning techniques that are based upon whteher the shrub blooms on "new wood" or "old wood". Shrubs that bloom on "new wood" can typically be pruned during the late Winter or early Spring, while shrubs thast bloom on "old wood" (from the previous year's growth), should not be pruned until after they have bloomed. And there's hundreds of species of shrubs. So, you see why it is impossible to address every pruning technique for every shrub, here, on this one page. But there are two basic types of pruning cuts that can be made.
TIP: Use the Search at the top of any page on our website to look up a specific variety of plant by common or botanical name. When you find the plant you are looking for, you can visit its Plant File page where you can find specific pruning instructions.
The Two Basic Cuts: There are two basic types of pruning cuts:
Heading Cuts:Heading cuts stimulate growth of buds closest to the wound. The direction in which the top remaining bud is pointing will determine the direction of new growth. Make heading cuts selectively to reduce shrub height and retain natural form. Non-selective heading cuts made indiscriminately will stimulate rapid regrowth from buds below the cut. These vigorous shoots are unattractive and make shrubs bushier, but not smaller. Non-selective heading cuts are only justifiable when using hedge clippers on a hedge or topiaried shrub.
Cutting plant stems back to a bud, twig or stub using heading cuts can lead to potential problems - a stub is often left and may become infested with insects or diseases, vigorous growth may be stimulated, and the new growth may be weakly attached and could split or crack under pressure. This may also negatively affect the desirable, graceful arching habit of some shrubs.
Thinning Cuts: Thinning cuts remove branches at their points of origin or attachment to another branch. Used in moderation, thinning cuts reduce shrub density without stimulating regrowth. Make pruning cuts correctly. For heading cuts, prune 1/4 inch above the bud, sloping down and away from it. Avoid cutting too close, or steep, or the bud may die. A "bud" is a small protuberance on a stem or branch, sometimes enclosed in protective scales and containing an undeveloped shoot, leaf, or flower. When pruning above a node with two or more buds, remove the inward-facing ones. A "node" is the place on a plant stem where a leaf is attached. Make thinning cuts just above parent or side branches and roughly parallel to them.
There are advantages to thinning cuts - No stub is left, the plant retains its natural shape, and vigorous new shoot growth is avoided. Caution: removing more than about 30% of the foliage can stimulate new growth even if thinning cuts are used.
TIP: Don't coat pruning cuts on shrubs with paint or wound dressing. These materials won't prevent decay or promote wound closure.
Aside from heading and thinning cuts, there are techniques for "maintenance pruning".
Methods Of Pruning
Pruning for Shape
You may decide to prune a shrub for shape to bring relatively geometric forms into a landscape for specific purposes or intents, or to keep a larger shrub smaller than it would naturally tend to be.
This approach works best on very dense shrubs, which will fill in the trimmed spaces very quickly and make it look like they have naturally grown into this shape.
Before pruning, you need to step back and visualize the ultimate shape of the shrub. You will cut back each branch to a leaf or bud closest to the point on the surface of the end shape. For best results, do this pruning in early spring before new growth has emerged, unless of course it is a spring-bloomer. Trim off all branches that extend beyond the desired shape you want.
Maintenance Pruning
Some shrubs simply require a once a year light maintenance pruning to to keep them healthy and in scale with their surroundings.
Many shrubs can benefit from light pruning beginning at time of planting and then on a once-a-year basis. In general, most shrubs can be pruned while dormant in late Winter, or after they've bloomed in Spring. Keep in mind that dormant pruning of a spring-flowering shrub will remove not just stems, but bloom buds as well.
When pruning a shrub always remove dead, diseased, or broken branches. When pruning dead or diseased branches, make thinning cuts into healthy wood, well below the affected area. Disinfect tools between each cut with products such as "Lysol," "Listerine," or rubbing alcohol. Tests have shown that "Pine-Sol" and household bleach are highly corrosive to metal tools.
In general, to reduce the height of shrubs with a cane habit (Forsythia, nandina etc.), first remove the tallest canes by cutting or sawing them out near ground level. Then, thin out any canes crowding the center, as well as those growing in an unwanted or unruly direction.
For height maintenance of mounding-type deciduous shrubs, prune only the longest branches. Make thinning cuts well inside the shrub mass where they won't be visible. This method reduces mounding shrubs by up to one-third their size without sacrificing their shape.
Large-growing shrubs, with a tree-like habit are the most difficult to shorten. After removing any rubbing branches, prune to open up the center of the shrub. Keep the crown open and maximize light penetration by careful use of thinning cuts. Prune branches that touch the ground and suckers originating from the roots. Wait until the very end of the job to make any heading cuts. Tree-like shrubs can usually tolerate removal of one-eighth to one-fourth of their branches.
TIP: Use the Plant Search to find any or all varieties of low-maintenance shrubs that require little if any pruning. When using the Plant Search, simply select your USDA Zone, then "Shrub" under TYPE, and then "Low Maintenance" under ATTRIBUTES.
Shearing Formal Hedges
Formal hedges are pruned in a totally different way than other shrubs or shrub formations. With only a few exceptions, the proper way to prune a formal hedge is to create a top line that is plumb level, and not necessarily level with the ground below. If the hedge is planted on a slope, it would be appropriate to step the courses down as a series of terraces, with each individual tier still plumb level. On the other hand, informal or natural hedges are almost always pruned to follow the contours of the ground, and are never pruned as rigidly.
To prune a formal hedge to plumb level, hammer in two posts or stakes at each end of the hedge or tier of the hedge, and slightly off to one side. Tie a string taught between the stakes, and then use a line level (a little level which hooks on to the string) to set the string perfectly level to plumb at the desired height of the hedge. Run your pruning tool along the string to remove the top of the hedge along the entire length of the string, being careful not to depress the string in the middle. This task is easiest with a set of power hedge trimmers, but can be done with standard pruning shears as well.
The sides of a formal hedge should also be pruned. In most cases, these are pruned with a gentle slope away from the vertical going down such that the hedge is slightly wider at the base than at the top. This will ensure that the leaves along the side receive adequate sunlight to keep them dense and healthy.
Rejuvenation Pruning
Older shrubs often grow out of proportion with their surroundings, and may have large amounts of unproductive wood. Two techniques are used to restore old shrubs, provided they still have sufficient vigor and are growing in a favorable location. Keep the following in mind with rejuvenation pruning:
- Select an appropriate species. Not all shrubs respond well to drastic pruning. When in doubt, ask your local professional nurseryman or arborist.
- Observe proper timing. The preferred time for renovative pruning is just before emergence of new growth(bud break) in early spring.
- Give extra care to heavily pruned shrubs. Fertilization, watering, and pest control will be critical factors
- Consider the shrub's new appearance. What will be the immediate impact on the landscape?
- The first technique involves complete removal of the entire plant 6-10 inches above the ground. Use heavy lopping shears and a pruning saw. Remove half of the new canes that develop by mid- summer, and head back some of the remaining canes. When using a heading cut, be sure to prune to outward-pointing buds so that the inner portion does not become too dense. Note that this does not work with all shrubs; it is most effective for shrubs that are highly multi-stemmed and which tend to freely send shoots from the crown, or those which tend to sucker from the base. Some shrubs that tolerate extensive rejuvenation are: abelia, dogwood, honeysuckle, hydrangea, lilac, mallow, rose-of-Sharon, spirea, butterfly bush, Annabelle hydrangea, and St. John's wort (hypericum). If in doubt, find out first whether a particular shrub will tolerate this kind of pruning; a wrong decision here may leave you with an empty space where a shrub once thrived.
- The second technique for shrub rejuvenation removes growth more gradually. The first year, remove one-third of the oldest, unproductive branches. The next year, take one-half of the old, lingering stems. Finally, in the third year, prune out the remainder of the old branches. New, productive stems should quickly replace the old wood. This method takes longer to complete, but the shrub stays more attractive throughout the rejuvenation period.
Choose from a category below to find pruning instructions for other types of Shrubs:
Choose from a category below to find pruning instructions: