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Plant Answer Line Question

Keywords: Pruning trees, Trees--Care and maintenance

What is the definition of topping a tree?


The Morton Arboretum Tree-Care Handbook calls topping "indiscriminately sawing off large branches." (1994)

According to the Washington State Department of Ecology's Vegetation Management: A Guide for Puget Sound Bluff Property Owners (May 1993, p.23), the practice of topping usually refers to cutting the upper portion of the main leader (trunk) in conifers and to the removal of all branches at a particular height in deciduous trees. Topping is not advised.

Plant Amnesty has loads of information about topping - including why it should not be done - at the following link: 5 Reasons Not to Top.

Date 2019-05-15
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Plant Answer Line Question

Keywords: Tree staking, Pruning trees

I have two 15 foot maples (2-inch diameter trunk) in our front yard. They shot up with quick growth last year, which was very impressive.

Now, with the recent rains on their thick foliage, they are sagging to an extreme degree. One tree, to the west of the driveway, has its lead trunk bending over at a 90 degree angle -- it is now parallel to the ground, no longer pointing vertically.

Why can't my trees support themselves? Where is their strength? Are they in danger of breaking? Vertical growth is the goal here, not stooping, drooping, sagging maples.

Should I prune them, or tie them up, or let them droop?


From your description it sounds like your trees could benefit from some pruning and/or staking. In general the former option is better than the latter. If you find that, after pruning, your trees still droop, you will most likely want to stake them. The goal with pruning is to slowly train the tree so that its shape fits your needs and the tree's structure is sound. Below, are some websites that will help you prune and/or stake your trees. The last two sites address in detail the issue of young trees.

The City of Seattle offers general tree care information that may be useful, as well as a page on young tree care.

The International Society of Arboriculture (ISA) has a succinct page about how to prune a young tree.

The ISA also has a section on how to plant a tree. Scroll down to find a diagram that shows how to stake a tree.

The National Arbor Day Foundation's Nine Things to Know About Trees contains some pruning information as well.

A Grounds Maintenance Magazine column by Michael W. Dougherty of Tree Management Co. addresses the specific needs of young trees.

Lastly, the Urban Tree Foundation's Pruning page shows how to shape a young tree in order to strengthen its structure.

Date 2019-09-19
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Plant Answer Line Question

Keywords: Pruning trees, Magnolia

I have a Magnolia tree that is planted next to our house. This year, there were not very many blooms and the tree is getting rather bushy-looking. When is the best time to prune it and how much can be pruned?


According to the American Horticultural Society's book, Pruning and Training by Christopher Brickell (DK Publishing, 1996), mature Magnolias should not be pruned unless it is essential. Many species will bleed from pruning wounds, and should only be pruned from summer to before midwinter. Summer-blooming Magnolias can be carefully pruned to reduce size by removing selected branches. The book Pruning: A Practical Guide by Peter McHoy (Abbeville Press, 1993) recommends doing this in late fall or early winter.
Below is a link to an interesting discussion on the how and why of pruning a Magnolia, from University of British Columbia Botanical Garden's online forum.

Date 2019-06-08
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Plant Answer Line Question

Keywords: Australian plants, Pruning trees, Eucalyptus, Container gardening

I recently purchased two Eucalyptus gunnii trees and one E. dalrympleana, which are still in their pots. I have them in full sun, facing south. I have been watering them every day - is this appropriate? I know that the gunnii tolerates waterlogged soil.


All Eucalyptus prefer full sun and well-drained soil. They are very drought tolerant when established.
Source: Manual of Woody Landscape Plants, by M. Dirr, 1998, p. 352.

If your plants are in terracotta containers they will need daily water. If they are in non-porous containers you have a bit more leeway, but do not let them dry out while they are young.

Another consideration is whether you plan to grow these trees in containers permanently, or if you are going to be moving them into the garden. If you plan to keep them in pots, bear in mind that these trees will get quite large (70 feet tall by 20 or more feet wide), so you may end up needing to do a lot of pruning from the top as well as root pruning. Sometimes, even when planted out into the garden, urban gardeners with small lots will coppice a tree like Eucalyptus gunnii or E. dalrympleana annually so that it does not overgrow its site, and so that the rounded, juvenile leaves are maintained. See the Royal Horticultural Society's page on eucalyptus pruning for additional details.

If your plan is to move the trees into the garden, it is best to do it when they are relatively young and small, as Eucalyptus generally dislikes root disturbance.

Date 2019-09-18
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Plant Answer Line Question

Keywords: Arborist, Pruning trees, Conifers

An issue has come up within our local homeowners association regarding some of the evergreen trees in our common areas. The issue is that about 20 or so trees have "deformed tops" - the tree has grown straight, but in the course of nature, the top has either broken off in a storm, or the tree has grown irregularly, developing a "hook" or "lever" at the top of the tree. This has lead to considerable discussion and (unfortunately) argument within our association. A tree service was hired by our association and they recommended "topping" the evergreens with the "lever" on the top. They stated these "levers" become "sails" in the wind and weaken the trees. One side believes these trees are hazardous and should be topped for safety, the other side believes they should be left as they are.

Searching through resources on the internet has led me to believe that topping these trees is the worst thing that could be done for the future health of the trees, not to mention the effect on property values due to the unsightliness "topping" causes.

I am interested in obtaining any information on the subject and would be open to discussing this with an arborist if possible, preferably someone who is very familiar with northwest evergreens.


You are right to be concerned about topping. The discussion probably should be whether to remove the trees if they pose a true hazard, or leave the trees if they do not pose a hazard. A damaged leader can be remedied, but do not take my word for it! You need a CERTIFIED arborist. If the arborist is hired as a consultant he will not have any incentive to recommend work that is unnecessary (this is why I am suspicious of the tree-service company).

Here are two organizations to contact for referrals:
Plant Amnesty: Plant Amnesty (See also Plant Amnesty's page about topping trees.)
PNW Chapter of the International Society of Arboriculture (the organization that grants certification) www.pnwisa.org or Trees Are Good, the website of the International Society of Arboriculture.

You want someone who has experience with tree hazard evaluation.

Another source is Arboriculture by Harris, Clark and Matheny that discusses what to do when a conifer loses its leader.

Date 2019-08-16
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Plant Answer Line Question

Keywords: Pruning trees, Malus domestica

We have an apple tree in our back yard. Last year it produced more apples then we knew what to do with. We pruned it after last season and then this year was an off year and we only had a few apples. My question is do we need to prune it every year or only after a very productive year? We are very new at this so any pruning tips you have would be great as well!!


Many factors may have affected the fruit production on your apple tree, but the general rules on pruning are to prune young trees very lightly, and old trees more heavily, particularly if they have shown little growth.

Pruning is usually done when the tree is dormant (i.e., winter), but sometimes apples are pruned during the summer growing season (the main reasons to do this would be to improve fruit quality and quantity, to regulate growth and control vigor, and to reduce pest and disease problems. (An excellent resource we have here is Training and Pruning Apple and Pear Trees by C.G. Forshey, American Society for Horticultural Science, c1992.) Another thing to consider is whether your tree is a dwarf, semi-dwarf, or standard apple tree. Pruning differs for each of these.

The following factsheet gives basic guidelines for pruning fruit-bearing trees:

Pruning Apple and Pear Trees from Clemson University Extension

Below are useful webpages about pruning fruit trees, and apples in particular:

Pruning Tree Fruit from WSU Extension

Spring and summer pruning for apples from Oregon State University

We have many great books on this subject in the library if you need additional guidance.

Date 2019-11-07
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Plant Answer Line Question

Keywords: Pruning trees, Camellia

I bought 2 small camellias a year ago. Their height and width at maturity will be about 10' x 8'. One has 3 trunks. Now they are 4' tall and the stems are so close, they are rubbing together and the branches cross-mingled. The trunks have hardened and are about 1/2" to 3/4" in diameter. Should I prune crossing branches and stems? Should I limit them to one or two trunks? If so, when and how should I prune? My goal is to have them limbed up or narrower at the bottom with a low tree canopy beginning at about 4'. They just finished blooming. The variety is Kremer's.


Pruning the camellias when they are done flowering, but before they form new buds, should be fine. You are right to observe that crossing branches and branches which are very close will pose a problem as the camellias grow. In Cass Turnbull's Guide to Pruning (Sasquatch Books, 2006), the author recommends selective pruning to thin out a camellia. Start by removing any dead wood, and then look for crossing and rubbing branches, taking out some (but not necessarily all--you don't want to strip the plant) of the most obvious problem branches. Since you have young plants, you should not have too much thinning to do. Turnbull's book also gives instructions for arborizing your camellia by removing the lower limbs. She recommends that you observe the branching structure before proceeding, and visualize what the plant will look like if you remove some of the branches.

You may find this pruning guide helpful. See second page, section III on "Tree-likes."

The American Horticultural Society Pruning and Training book edited by Christopher Brickell (DK Publishing, 1996) suggests pruning a young camellia by shortening overlong lateral branches to an upward growing sideshoot. Selecting a central leader (main trunk) is also recommended.

Date 2019-10-02
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Plant Answer Line Question

Keywords: Pruning trees, Flowering cherries

I live in Seattle. My condo board is having a debate about whether pruning an ornamental cherry after May will kill it or not. Can you help? Also, when should it be pruned?


According to Cass Turnbull of the local organization, Plant Amnesty, the main reason pruning ornamental cherries is problematic is that the branch system of these trees is complex, and it is hard to tell (if you are not an experienced gardener or a professional arborist) what to prune. In her Guide to Pruning (Sasquatch, 2006), Turnbull says that ornamental cherries are prone to dieback if their branches are shortened. Besides the dieback issue, improper pruning can give rise to watersprouts (the branches grow straight up). I consulted two other pruning guides, both of which advised against any pruning of ornamental cherries.

Do you know why the board wants to prune these trees? If the trees are too large for the site, it might make more sense to remove them and plant something appropriate which will not require risky pruning. You may find this discussion forum from University of British Columbia Botanical Garden helpful.


"These generally disease susceptible trees resent severe heading back. Trying to force it to become a perfectly symmetrical shape will also destroy its natural character; much of the appeal of aged Japanese cherries (and related trees) is the contrast between the prettiness of the flowers and the rugged appearance of the trunk and branches."

My summary is that, while pruning the trees may not kill them outright, it could make them aesthetically unappealing and more susceptible to disease, so it would be best to let them be.

Date 2020-03-12
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Plant Answer Line Question

Keywords: Pruning trees, Malus domestica

Could you provide me with information on pruning Red Gravenstein?


I did not find a simple answer to your question about pruning Red Gravenstein. It seems that pruning is key, however, in controlling whether the tree fruits annually or biennially.

The book The Best Apples to Buy and Grow edited by Beth Hanson (Brooklyn Botanic Garden, 2005) has this to say about the Gravenstein apple: Prune and thin to control its tendency to bear a crop biennially.

From the book Apples for the 21st Century by Warren Manhart (North American Tree Company, 1995):

Classified as a biennial bearer, and understanding of its genetics can lead to getting some apples almost every year. Gravenstein is a triploid with 17 extra chromosomes, which means it is nearly sterile, incapable of very much self-pollination. In pioneer times it was typically planted with the old Tompkins County King, another triploid of fine flavor. The East Malling Research Station near Kent, England suggests that triploid varieties should have pollen from two viable pollenizers to properly set seeded fruit and to pollenize each other as well as the triploid.

The author further discusses not grafting to any rootstock larger than M9, M26, or M& unless you want to harvest fruit 20 feet off the ground.

From a contributor to a discussion on Rainyside Gardeners, a local gardening site:

"We don't have a Gravenstein, but we do have 7 other varieties of apples. Gravenstein bear heavily every other year. They should be pruned annually during dormancy. A simple rule of thumb is, anything that grows straight up or crosses another branch has to go. The straight up growths are called water sprouts, and take energy away from fruit production. Apples need to be thinned. One apple per cluster--remove the rest, save the largest one and pick off all the others. Apples should be at least two inches apart."

The book Training and pruning apple and pear trees by C.G. Forshey, D.C. Elfving, and Robert L. Stebbins (American Society for Horticultural Science, c1992) recommends using the central axis or French axe form for Gravenstein apple trees. Here is a description of this method:
"Vertical Axis. The vertical axis, sometimes called the French axe or the central axis, was developed by J. M. Lespinasse in France, and has performed extremely well throughout North America (Table 1). This system requires leader support to a height of 8 feet to 10 feet above ground and minimal pruning is used to develop a tall conical shape (Fig. 3)."

Another description from the University of California Santa Cruz Agroecology program:

Vertical Axis or French Axe


  • Tree Height -10'-14'
  • Spread at Base - 5'-7'
  • Space between Trees - 5'-6'
  • Tree Density - 500-700 trees/acre
  • Rootstocks - Mark, M9, M26, M7, M106
  • Support - Individual pole or wire trellis
  • Labor Needs - Low; very little pruning; all operations can be done from the ground
  • Cropping - 2-4 years

This system features tall, narrow trees. The aim of this system is to let the tree achieve a natural balance between fruiting and vegetative growth, to reach its ultimate height very quickly (2-3 years), and to come into fruiting early. The vertical axe features almost no pruning in the early years. As with the slender spindle, the aim is to establish a permanent lower tier of branches that are trained to a horizontal position and left long (unpruned). Because the leader is not headed (even at planting), the tree form is very narrow and height is achieved quickly.

Above the lower tier of branches, weak to moderate lateral branches occur randomly. This system also features fruit-bearing on the main leader, which eventually slows tree height, as fruiting is usually more effective than pruning at dwarfing trees. Eventually the leader is pruned into older lateral wood. As the branches in the top part of the tree extend later-ally beyond their desired length of 2-3 feet, they are thinned out or renewed by cutting back to a stub (1-2 buds). The disadvantages of this system are the height of the tree, which requires ladder work, and overly vigorous branches high in the tree, which can shade the lower portions of the tree.

The following article from Alameda County Master Gardeners describes how to prune tip-bearing apples (and pears). This might be of interest to you because Gravenstein is both tip-bearing and spur-bearing.

The Home Orchard Society site has an online forum for submitting questions as well.

Date 2019-08-02
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Plant Answer Line Question

Keywords: Pruning trees, Ficus carica

We recently moved into an old house with a huge fig tree in the back. We just missed this whole season's crop because I was waiting for them to turn brown but the birds got them all first. Then I saw some green figs for sale in the grocery store and it appears that some varieties don't turn brown. Is this true or did mine not ripen? Also, the tree is probably close to 30' and we'd like to add a screened-in porch under part of it. I'd really like to keep the tree and a good bit of fruit but I want it to grow more in the other direction. I've read that "hard pruning" is encouraged, but does that really mean cutting down a thirty foot tree? Do I need to do it in stages? What's the best size and shape and how do I get it there?


There are different types of figs, and some are green, some are brown, some are purple, as the images on the commercial site of Adriano's Fig Trees illustrate.

Figs should be picked when ripe, as they will not ripen off the tree. The California Rare Fruit Growers site has good general information on growing figs.

As for pruning, the best time to prune is late winter/early spring. To control height, open the center of the tree and remove any dead wood or drooping branches. I don't think radical pruning is the standard practice in maintaining a fig tree. University of Arizona article on growing figs describes pruning practices for several different varieties of fig.

Most pruning is best done when the tree is dormant, during the winter when it is leafless. Even during the spring and summer, however, you can start by removing all branches and stems that are obviously dead.

The rest depends on how your tree is growing (single trunk or multi-stemmed), what kind of results you would like (how large, small or what shape) and how long the tree has been unpruned. Our rule of thumb is to go by thirds. Remove about a third of the wood that you would eventually like to have gone. On multi-stemmed figs that are becoming large, we recommend selecting a few oversized stems and thinning those out to the ground, rather than "heading" all the branches to stubs. Let the tree rest for the summer and see what new growth appears. We recommend keeping fig trees small enough that all the fruit can be easily reached from the ground but in some areas of the south and southwest, folks treasure the deep shade of the larger figs. The final shape and size are up to you.

A 2006 article by Bunny Guinness in the British newspaper the Telegraph also describes how to prune an older fig tree. Excerpt:

"Figs really are a lazy man's fruit and, once they have had their formative training, mature trees or wall-trained shrubs do not need much attention apart from some replacement pruning. This involves removing one of the seven or so main limbs every three to four years in March or April, to stop the whole bush becoming too old and unproductive. Apart from this, providing you have the wall space, you can leave well alone. I have seen many such 'neglected' plants, and they still fruit well, although perhaps not as well as they might.

"On the other hand, if you want to maximize your crop (assuming it is against a wall), buy a copy of Clive Simms's Nutshell Guide to Growing Figs (Orchard House) to see how to fan train it against a wall--it is not hard. Once you have established an approximate fan of branches, you can start the ongoing pruning regime.

"Firstly, remove any weak branches in winter. Then, in April, remove the very tips of the main branches, above the developing figs. This will encourage side shoots, which are summer-pruned by cutting back in June to about four leaves. This technique can almost double the crop and bring it forward by a couple of weeks. Do not be tempted to cut back hard in winter, unless you don't mind forgoing a lot of your crop--this will cause lots of new growth but little fruit."

Date 2020-03-13
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Plant Answer Line Question

Keywords: Ficus carica, Pruning trees, Espaliers

I purchased a fig tree and my property has very limited space. There is an ideal strip of land by the south side of the wall that gets plenty of sun. I read that fig trees should be planted near a south facing wall, but my only concern is how close can it be to the side of the house. The strip of land is only about 2 feet wide and I also read that fig roots are shallow and spread beyond the canopy. I'm worried that the root system would cause damage to the foundation/basement.


The roots of a fig tree may be shallow, but they may spread out as much as 50 feet, and if the soil conditions are right (soft, permeable), roots may go as much as 20 feet deep. I think planting so close to the house is not ideal, unless you were to have a dwarf variety of fig in a container (such as Petite Negri or Negronne). If there are any cracks in your foundation, then tree roots may be a concern. Tree roots do not usually penetrate a solid wall, although as they grow and expand, they can exert pressure on surfaces. The other concern with planting that close is that you will find you frequently need to prune branches away from the house. There is a tradition of growing fig trees as espalier forms (trained to grow flat, on one plane), but to do this you need to restrict the tree's roots in a container. Below are links to information on how to do espalier:

Mississippi Cooperative Extension

Royal Horticultural Society

The following links have excellent general information about growing fig trees:

Purdue University Extension

California Rare Fruit Growers

Here is information from Reads Nursery, a British fruit specialist. Excerpt:

Allow 8' - 15' horizontally and 6' - 10' in height per plant. Root restriction is required. Construct a box of 2' square paving slabs 4' x 2' against a wall or side of greenhouse, leaving 3 inches showing above ground. Put 9 inches of rammed brick rubble in the bottom and fill up with good soil such as John Innes No 3.[*This is a British product--you can use compost instead.] When planting loosen root ball carefully around the outside and plant 1-2"deeper than before. Water in well. Pruning. Treat as for Figs in Pots but, on a wall, the plant should be fan trained on horizontal wires 12 inches apart.

Date 2019-10-03
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Plant Answer Line Question

Keywords: Quercus palustris, Pruning trees

I have a big pin oak that needs to be pruned. Maybe 1/3 of the leaves have dropped. Is this a good time to prune or should I wait a week or two?


The American Horticultural Society's Pruning & Training (DK Publishing, 1996) says to prune pin oak (Quercus palustris) as you would white oak, that is, when the tree is dormant, in winter or early spring. Pin oak can be trained as a central-leader standard, but if this is a mature tree which was not trained this way, do not attempt it now. Established trees should not need much pruning at all, so only prune what is dead, diseased, or damaged, or any branches which are drooping, in order to provide clearance.

The Sunset Pruning Handbook (1983) says the following: "Pin oak is a pyramidal tree when it's young. It forms a rounded top as it matures. during the pyramidal stage, its lower branches are down-sweeping. If you remove the lowest branches to gain walking space beneath the tree, the limbs above will bend into a down-sweeping position. When the tree is mature, the down-sweeping process will stop. You can then cut off lower limbs to create a tree suitable for walking under."

Date 2019-05-18
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Plant Answer Line Question

Keywords: Pruning trees

Is it possible to arborize a large Euonymus shrub (by selectively pruning many of its branches to create a tree shape), as one can with rhododendrons? I prefer pruning over removal, if that option is available to me. What tips can you offer for pruning Euonymus in this way?


It is a little difficult to offer advice without knowing which species of Euonymus you are growing. There are many, some evergreen and some deciduous. The pruning method varies according to the species. See the link here, from Oregon State University, for information on some of the different species.

If you would like to get back to me with information about the species, I will be better able to assist you. For now, here is general pruning information and links which may be of use.

Seattle gardening expert Cass Turnbull and the organization Plant Amnesty offer helpful pruning hints. Excerpt:

Punch List for Tree-Likes. Take out:

  1. Dead wood
  2. Suckers from trunk, roots, or branches
  3. Crossing/rubbing branches (the worst ones)
  4. Branches hanging on the ground
  5. Wrong-way branches
  6. Too-far-up/too-far-down branches
  7. Parallel branches
  8. Head back to shorten (if necessary) on shrubs, not trees.
  9. Tree-likes vary in the degree to which they may be thinned before they sucker back or suffer dieback. Removal ranges from approximately one-eighth to one-third total leaf area.

Another excerpt, on arborizing shrubs:

Other people strip up all the lower limbs of shrubs they consider too big, making them somewhat reminiscent of lollipops or ostriches. I hesitate to mention stripping because of these common abuses. However, there are some instances where removing the lower limbs of a shrub is a good option. It will depend on the type of plant and its location. Don't strip up plants just because they seem too big. Good candidates are ones that are actually impeding foot traffic or totally obscuring windows. The best subjects are non-suckering tree-like shrubs. Usually they are broad-leafed evergreens, such as rhododendrons, pieris, camellias, or strawberry trees (Arbutus unedo). Stripping up works best on very old shrubs. By cutting off the lower branches you are "arborizing" them. "Arbor" means tree, and you are turning your big shrub into a small tree. English laurel is a good subject. Instead of a giant oppressive blob, you can have an open, sort of oriental-looking, small tree. In fact, one could say that most of these plants are trees in their native habitats. They start out as shrubs and grow into understory trees in their adulthood. We just expect them to stay in the shrub-like juvenile stage forever.

Some shrubs can be arborized, meaning that they can be pruned into small trees.

Pause before you strip, though. It's a major step. Look inside your shrub and evaluate how the trunk will look when it's exposed. Is it fat? Good! Does it lean and curve gracefully? Great! If possible, endeavor to leave some branches lower down and inside to avoid the stripped or gutted appearance. To alleviate the lollipop effect, thin out the upper canopy of leaves, too. It should look a bit lacy and like a tree, not like a solid ball. Don't arborize more than a few plants in your landscape, it begins to look silly if you do too many.

Be sure to leave enough leaves to collect sunshine in order to feed the plant. Shrubs and trees vary from species to species in the degree to which they will let you put them on a diet. Trees and shrubs which have been starved by over thinning usually succumb to death in a drought or freeze. Be sure to help heavily thinned, non-suckering plants by supplying sufficient water and fertilizer.

Date 2019-08-02
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Plant Answer Line Question

Keywords: Acer palmatum dissectum, Pruning trees

How do I go about pruning my laceleaf Japanese maple, and when should I do it?


Cass Turnbull's Guide to Pruning (Sasquatch Books, 2006) specifically addresses the pruning of laceleaf Japanese maple (Acer palmatum dissectum). To summarize, she advises combing out any dead leaves, and then thumb-pruning tiny dead twigs (light gray in color). Remove dead or dying branches, especially near the bottom and inside the tree, working from the bottom up and the inside out. She likes to do summer pruning on this type of maple, but early winter is also acceptable.

You can find additional information on pruning from the local organization Plant Amnesty, including an instructional video in which Plant Amnesty founder Cass Turnbull demonstrates how to prune a laceleaf Japanese maple.

Date 2019-10-03
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Plant Answer Line Question

Keywords: Arbutus unedo, Pruning shrubs, Osmanthus, Quercus, Viburnum, Pruning trees

When is the proper time to prune Arbutus unedo? How much can be pruned at a given time? Same question for Osmanthus decorus, Viburnum odoratissimum, and Quercus reticulata.


According to The American Horticultural Society's Pruning & Training edited by Christopher Brickell (DK Publishing, 1996), you can prune Arbutus unedo in spring, as soon as danger of frost is past (that would be early April in Seattle), but keep pruning to a minimum. Some people choose to remove lower branches to create a taller trunk on younger trees.

The book Pruning: A Practical Guide by Peter McHoy (Abbeville Press, 1993) says that Osmanthus decorus can be clipped in late summer. If you want to limit its size without clipping, prune back long shoots to points far inside the shrub in late spring or early summer, after flowering. If the plant is overgrown, you can spread this type of pruning over two or three years, but do not do it annually. I am not familiar with this species of Osmanthus, but I do know Osmanthus delavayi, and grow it as a hedge. It is sheared after it flowers, and then probably two more times before winter. I did have to prune the top back quite hard last year, and this did not seem to cause any problems, but O. decorus may have different needs.

I could not find information about Viburnum odoratissimum specifically, but most pruning books have general guidelines for Viburnum species. Unless you do not mind losing the flowers, it is best to prune when flowering is done. If you are growing V. odoratissimum as a tree, then special pruning may be needed. George E. Brown's The Pruning of Trees, Shrubs and Conifers (Timber Press, 2004) says V. odoratissimum is somewhat tender, and may grow best as a standing bush with the protection of a wall, using ties in places to keep it close to the wall. The only pruning he mentions is cutting out older wood after flowering, and tying new growth back to the wall (if you are growing your plant in a site where you can do this).

According to the Peter McHoy book, oaks do not require routine pruning. Brown's book says not to prune oaks between mid-spring and mid-summer, as a means of protecting against oak wilt and beetle infestation. If you must prune, do it in winter.

Quercus reticulataPlant Amnesty's referral service or the Pacific Northwest Chapter of the International Society of Arboriculture.

Date 2019-09-19
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Plant Answer Line Question

Keywords: Cupressocyparis, Pruning trees

The previous owners of our home planted Leyland Cypress at the property line. The trees have grown very high. The neighbors have asked us to trim these trees in a "hedge-like" fashion, which means that we would need to cut the tops of the trees. One neighbor, who is a landscaper, insists this will not damage the trees. But several arborists have advised not to "top" the trees. We are willing to have the trees topped as long as this will not compromise the health of the trees.


Pruning Leyland Cypress (x Cupressocyparis leylandii) to look like a hedge can be a challenge.

Topping is not a recommended method for controlling trees, because it often causes them to grow faster (unless they are topped mortally) and thus must be done repeatedly and expensively, and also because it weakens the tree, which may cause it to drop limbs, rot, or blow over more easily. The group Plant Amnesty has a great deal of information about why one should avoid topping.

However, topping may be less harmful for x Cupressocyparis leylandii than for other plants, but it is still not a particularly effective solution. The University of Florida Extension concurs that this practice is less harmful to x Cupressocyparis leylandii than it is to other species, but they still do not recommend it.

Peter McHoy's A Practical Guide to Pruning (New York: Abbeville Press Publishers, 1993)also advises avoiding topping, but also notes that if one must top an x Cupressocyparis leylandii, it should be done in midsummer and repeated every few years.

However, in general, it would appear that topping is very much a last resort.

One book, Practical Tree Management: An Arborist's Handbook, by T. Lawrence, P. Norquay, and K. Liffman (Melbourne: Inkata Press, 1993), recommends that "Where a tree requires severe reduction or radical alteration of its aesthetically pleasing, natural growth habit, it is usually far better to consider replacing the tree with a species more suitable for the situation..." Thus, you may consider an initial pruning and eventual replacement.

Date 2019-10-10
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Plant Answer Line Question

Keywords: Magnolia grandiflora, Canker (Plant disease), Parrotia, Pruning trees

I have two questions. When is a good time to prune Parrotia persica?
What can I do about a canker on the trunk of a Southern Magnolia?


According to the American Horticultural Society's Pruning and Training (edited by Christopher Brickell; DK Publishing, 1996), Parrotia persica should not need a great deal of pruning, but if you do prune, it should be from fall to early spring.

If you are growing it as a shrub-like shape, you should not thin or shorten laterals, as this will cause congested growth. If you are growing it in a tree-like form, the trunk can be cleared to about 5 feet, allowing the crown to branch. If needed, you can shorten pendulous tips to give clearance for walking beneath the tree. Once established, this tree should not be pruned. If the tree was a grafted specimen, remove any suckers.

This information from University of Florida discusses Southern magnolia (Magnolia grandiflora), and says that cankers may kill branches, but the affected branches may be pruned.
"Canker diseases will kill branches. Cankers on branches can be pruned out. Keep trees healthy with regular fertilization and by watering in dry weather."
Magnolias by Rosemary Barrett (Firefly Books, 2002) says that "various cankers, such as nectria canker, dieback and trunk decay can all be dealt with by cutting out the dead or diseased wood. Rarely will any of these diseases cause the death of the plant."

Date 2019-05-18
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Plant Answer Line Question

Keywords: Thujopsis, Pruning trees, Conifers

I'm looking for resources on proper pruning or rejuvenation for Thujopsis. We have a 50-60 year old specimen.


According to Michael Dirr (in Dirr's Hardy Trees and Shrubs: an Illustrated Encyclopedia), Thujopsis dolabrata is "too beautiful to mutilate with pruning shears." This website of a Seattle-area gardener suggests that you may be able to prune it lightly by candling the leader.

According to George Brown's The Pruning of Trees, Shrubs and Conifers (Timber Press, 2004), specimens of this tree vary widely in habit. Some form a definite leader, while others are "untidy, spreading shrubs. Of those which grow out of this shrubby habit, a number produce rival leaders and the result is a small tree made up of slender upright trunks with their supporting branches." If your tree has multiple leaders, it is probably too late to prune them--this kind of pruning would be done on a younger tree.

I spoke with a docent at Seattle's Japanese Garden, which has Thujopsis, and she said that they are not pruned, except to remove dead, damaged, or diseased branches. You may find this general information on pruning conifers from Brooklyn Botanic Garden useful.
"As with any plant, dead or diseased conifer branches should be removed immediately, regardless of the time of year. Any other pruning should be done when the plant is dormant. Unlike many deciduous shrubs, most conifers can't re-sprout from older wood (yew, arborvitae and podocarpus are exceptions), and so a good rule of thumb is never to remove more than one-third of the total growth at a time. If you prune too drastically, the plant may never fully recover. Many of the dwarf varieties never need to be pruned, but do appreciate some thinning to allow air and sunlight to penetrate to the interior of the plant.
The most common method of pruning evergreens is known as 'cutting' or 'heading' back. Only part of the branch is pruned; the terminal or tip growth is trimmed to side or lateral buds or branches. This promotes thicker, more compact foliage and a smaller overall plant."

It sounds as if you should do the bare minimum in terms of pruning. If you really need to reduce the tree's size, it would be wise to consult a certified arborist.

Date 2019-09-11
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Plant Answer Line Question

Keywords: Carpinus, Pruning trees

I have a small hornbeam tree, Carpinus japonica, roughly 6 feet tall. It has never been pruned and was just transplanted to a small shade garden, close to a path. It will need to be pruned to keep the canopy high. Should this tree be pruned lightly? Is it at a good age or time to prune and to make a single trunk tree? Would fall be the best time to prune?


According to the American Horticultural Society's Pruning & Training (edited by Christopher Brickell, DK Publishing 2011), Carpinus species tolerate pruning well, but it is best to do it from late summer to midwinter, to avoid severe bleeding of sap. Your tree is quite small, and it should be fine to do light pruning and remove any branches that are going to interfere with the path. (Heavy pruning can result in twiggy growth.) It's not uncommon to prune it to a central leader standard (more upright form).

Date 2019-07-19
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Garden Tip

Keywords: Pruning trees, Pruning

Winter is a good time to prune because the branch structure of trees and shrubs is clearly visible. Winter is certainly not the only time for pruning, but the list of competing garden chores is typically shorter in winter. Here are a few websites to check out before pulling out the pruning saw:

Date: 2006-03-20
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Garden Tip

Keywords: Pruning trees, Pruning

By Thanksgiving most leaves have fallen off deciduous trees. Some people feel a strong desire or obligation to prune when they see these naked trees. If you're one of these people remember that most trees and shrubs don't require regular pruning, other than to remove dead, dying or diseased branches. However, if some correction or thinning is necessary arm yourself with one of the excellent pruning books:

  • Cass Turnbull's Guide to Pruning: What, When, Where & How to Prune for a More Beautiful Garden (Sasquatch, $17.95) - Turnbull demystifies pruning with humor and helpful diagrams.
  • The Pruning of Trees, Shrubs and Conifers by George Brown (Timber, $29.95) - This classic reference work has been revised and enlarged by Tony Kirkham to reflect recent advancements in pruning; it includes a plant by plant guide to special considerations.
  • An Illustrated Guide to Pruning by Edward Gilman (Delmar, $26.25) - A text book for professionals or serious gardeners, this book includes information on training young trees and has many illustrations.

Date: 2007-04-03
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Garden Tip

Keywords: Pruning shrubs, Plant training, Pruning trees, Pruning

American Horticultural Society Pruning and Training. Christopher Brickell, editor. New York: DK publishing. 1996
This book gives detailed instructions on how and when to prune trees, shrubs, fruit trees, vines and roses. With good basic background information on general pruning techniques, pruning guesswork is eliminated. The book also explains how to do specialized methods of training like turning your hedge into a living sculpture.

Date: 2007-07-12
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