How to trim tree roots?

One of the questions I am most frequently asked is, “How often do you root prune?” This is a tricky question and one for which I wished there were a more clear cut answer. First let’s dispel a myth. Ready? Ok, here it is. We do NOT root prune every tree in the nursery. (Take a minute and digest that one, sit down if you need to.) Now that you are over the shock, I’ll tell you why we don’t.

First, let’s talk for a moment about what exactly root pruning is. Root pruning is just what it sounds like: cutting roots just as we would cut branches, only we do it with a tree spade, a shovel, or a trenching machine. Some of the reasons to prune a tree include:

Timing

Some trees might need to be dug in a less than preferable season. For example, oaks typically do not dig especially well at any other time than when they are dormant. But let’s say that the trees might not be needed until July. We would then choose to root prune the trees during dormancy to help prepare the trees for digging outside of their optimal season.

Slower growth

I often like to say that trees are not multitaskers; most are only capable of doing one thing at a time. They can either put out new roots, or new leaves, but not both at the same time. Root pruning a tree will often slow down the growth of the tree. By severing their roots, it forces the tree to put energy into regeneration of new roots rather than primary and secondary growth (getting taller and putting on caliper). And more roots are good, right? RIGHT!

Smaller rootball

Because a root pruned tree will have a higher concentration of roots in a closer proximity to the trunk of the tree, we are often able to put a root pruned tree in a smaller root ball. This turns into a win-win for those projects that cannot accommodate a larger ball size or a large piece of equipment. This also ties in nicely to purposefully slowing down the growth of a tree.

Long-term benefits

The benefits of root pruning are realized for more than just one season. A tree that was root pruned in 2013 will be more easily dug in an off season for likely two to three years beyond the date of the root pruning.

In a recent demonstration, we root pruned a red maple in early spring (we actually root pruned it for a demonstration on bare-rooting that was rescheduled for a later date). The preparation work we did for this demonstration provided an excellent study in just how effective root pruning can be at creating new roots! In the photo below, you can see how many new fibrous roots were generated in just four months’ time.

Will you just look at those gorgeous roots! You can’t have lustrous hair without a trim every now and again, the same may hold true for the roots of many species of trees.

So, knowing what we do about the many great benefits that root pruning can realize, shouldn’t we just root prune each and every tree in our nursery? In a paragraph above, I mentioned that root pruning will often slow down the growth of a tree, making it a great way to control growth in fast growing species such as Liriodendron (tulip poplar) and Prunus (cherries). But what about Fagus (beech) or Gingko? Slowing down these already slow growing species would result in longer than average growth times, resulting in fewer available trees.

Another simple – and honest – reason for not root pruning is time, or more specifically the lack thereof. Root pruning is time consuming. Each year we root prune (or plan to root prune) a certain number of trees so that we can expand on the typically short harvest window. Root pruning in the spring allows us to dig throughout the less than desirable digging months of summer. We mark these trees with a special color of ribbon and a silver tag with their root prune date on them so that we can track their history and progress.

Some trees need to be prepared months and sometimes even years in advance, so knowing when your projects will be installed is a critical first step for the success of its trees. Find a nursery that you can trust and with whom you can develop a relationship and you are sure to see a difference in the quality and performance of the trees.

Ronda Roemmelt is the sales manager and representative for Mid-Atlantic sales at Ruppert Nurseries in Laytonsville, MD. In addition to 20 years of industry experience, Ronda also has a Bachelor of Science in Agricultural Science from Pennsylvania State University with a minor in Horticulture. Ronda is a Certified Professional Horticulturalist and an ISA Certified Arborist.

Ann Larle Valentine / CC BY-SA 2.0

Removing Tree Roots Above Ground: Will It Harm or Kill the Tree?

Roots stretch far and wide to give our trees a stable foundation. But what happens if they grow a little further than we’d like?

One of our readers, Paul, recently asked, “How can I get rid of the roots from my tree that have grown into my front yard and are killing the grass?”

Dealing with roots can be tricky—an improper cut could affect the tree’s water flow or cause it to fall in a storm. That’s why it’s important to take a safe approach.

Read on to learn if you can prune above-ground tree roots, how many tree roots you can cut at once and how to safely prune tree roots at the best time.

Cutting Tree Roots Above Ground – Everything You Need to Know

If I cut a root, will the tree die?

It all depends on the size and location of the tree root.

As a guideline, avoid pruning roots more than 2 inches wide. Removing large tree roots can make the tree unstable or unhealthy later on. If large roots are removed, the tree may not be able to get enough nutrients and water. Also, don’t remove roots close or fused to the trunk since these are critical to the tree’s structure.

What’s the best time of year to cut tree roots?

If you choose to cut or remove tree roots, winter and early spring are the best time of year to do so.

How many tree roots can I cut?

Never remove more than 20 percent of above-ground tree roots at once. Then, wait two to three years to make sure your tree fully recovers. Only then can you safely consider cutting more tree roots.

How can I cut tree roots without killing the tree?

Again, if you cut tree roots, there is never a guarantee that it won’t hurt or eventually kill the tree. We only recommend removing tree roots when they are damaging or infringing on a nearby structure – not for aesthetic reasons.

For the best chance of your tree surviving, consult with your local arborist before removing tree roots. Or see if your arborist can prune the roots for you.

For DIY root cutting, use this step-by-step guide.

1.) Find the root posing an issue and trace it back to the base of your tree. If it turns out to be part of a large root, ask your arborist before pruning or cutting. For a smaller root, move to step 2.

2.) Measure the diameter of your tree. Wrap a measuring tape around the tree, four feet from the tree’s base. Then, divide that number by 3.14. Generally, you can safely prune roots that are 3-5 times the diameter away from your tree. So, if your tree has a diameter of 3 feet, only cut tree roots 9-15 feet away from the tree.

3.) Mark the area you’ll cut, and dig a hole all the way around the root until it is completely exposed.

4.) Use a root saw to prune the tree. Carefully pull the root up and away from the tree until it comes out. Be sure to refill the hole with soil from the same area afterward.

5.) Keep an eye on your tree for a few weeks after pruning. Signs of decline like yellow leaves or branch death call for an arborist’s immediate attention.

Root pruning guidelines

Home > Root growth > Root pruning trees > Root pruning guidelines

Trenching and digging in the soil near trees can cut roots, and this can damage the tree resulting in tree decline or the tree falling over (See: fallen tree from cutting roots). This can cause liability and safety concerns. Root pruning is more injurious to old mature trees than it is for younger more vigorous trees. Cutting roots greater than about one inch diameter during trenching and digging can mean problems for the tree. In some cases roots of one to three inches diameter represent the major structural roots holding the tree upright.

The impact from pruning roots depends on several factors (see table below). Damage typically increases with more cuts, bigger cuts, and cuts made closer to the trunk. Root pruning, trenching, and other construction activities close to the trunk result in more injury on shallow, compacted soils or on soils that drain poorly than on well drained soils. This is due to the shallow roots common on sites with shallow soils or high water table. Trees that are leaning are poor candidates for root pruning. Prune roots only with sharp tools to avoid tearing behind the cuts.

See: more details on cutting roots.

Factors affecting response of trees to root pruning

  • root size: larger roots may generate few new roots
  • number of cut roots: more roots cut means more tree stress
  • proximity of cuts to the trunk: the closer cuts are to the trunk the bigger the impact
  • species: some species tolerate it better than others
  • tree age: old trees are more likely to stress and die
  • tree condition: trees in poor health should not be root pruned
  • tree lean: leaning trees should not be root pruned
  • soil type and site drainage: shallow soils mean stay farther from the trunk

How close to the trunk can roots be cut?

Well, the answer appears to depend on who you ask. For mature trees, some experts recommend not cutting roots closer than 6 to 8 inches from the trunk for each inch in trunk diameter. That means stay at least 10 feet away from a 20 inch tree! Others are more realistic and state that we should root prune no closer to the trunk than a distance equal to 3 times the trunk diameter, preferably 5 times the trunk diameter. Dr. Tom Smiley at the Bartlett Tree Research Laboratory in Charlotte showed that roots on one side of very young trees can be pruned off completely at a distance equal to 5 times the trunk diameter without any impact on tree stability. Which ever rule-of-thumb you decide to use, do so knowing that pruning roots on trees can result in trees falling over or dying. While root pruned large trees on well drained soil may not fall over because of deeper sinker roots under the trunk, they can and have. There are fewer deep roots holding the tree up on poorly drained and compacted soils.

Alternatives to root pruning

  • add soil over the roots and re-sod
  • curve the sidewalk around the surface roots
  • elevate the walk over the roots
  • suspend the footing on pilings
  • re-pour the walk with steel in the concrete
  • grind the concrete down
  • raise the walk by injecting grout under it
  • build the structure elsewhere
  • dig under roots with trench-less technology
  • live with the problem
  • See: more details on alternatives to root pruning

Can I cut off exposed tree roots without harming the tree?

Removing large or major roots from a tree is going to have a detrimental effect on the health of the tree i.e.

  • Weaken it from a structural point of view.
  • Put it into shock, stress.
  • The wound(s) caused by the removal of such roots can allow disease to enter.

Any of those could easily lead to the tree dying.

Removing “sucker” roots, if done properly, should have no long term negative effects on the health of a tree, assuming they weren’t sent up as a sign of stress (see below), even then they can be removed as the tree has much greater problems that need addressing (if possible, feasible to-do-so)…

Some trees by their very nature are prone to send up “sucker” roots eg

  • Anything in the Ficus genus via below comment from Lisa

  • Black Locust

  • White Poplar

Other times “sucker” roots can be a sign a tree is in stress, and those roots have been sent up (above ground) as a survival mechanism eg

  • Underground roots have been damaged

  • Overlay compacted soil

  • Drought (lack of moisture in the soil)

To remove “sucker” roots, use an appropriate sized pair of hand pruners or a pruning saw, make sure the pruning tool is shape and the cutting area is clean (use something like rubbing alcohol or a mixture of one part household bleach to 10 parts water). It’s good practice to clean your pruning tool after working on each tree (plant, shrub, etc), as doing so helps prevent the spread of diseases if present. If you’re really concerned about diseases being spread, you can of course clean your pruning tool after each cut.

Remove the “sucker” roots via a clean cut, either at:

  • The soil line (or as close as possible to the soil line)

  • Just below the soil line, accomplished after careful removal of the surrounding soil to allow such a cut to be made. The soil can be returned to the area once the cut has been made.

Do keep in mind, just because you remove “sucker” roots once does not mean the tree will not send up more, in fact you might find the tree sends up even more…

“Honey, I am so tired of looking at those roots in our front yard! I’m going to have the neighbor’s gardener, Joe Schmo’s Tree, Landscape, Automotive Repair and Concrete Service come over and cut them all out, okay?”

Whoa there, Nellie!!

There are many reasons why one sees roots in their lawn, and it isn’t necessarily because the tree is unstable or looking for water. Before you take a hatchet to those roots you first need to know what they do, why they are there and the law of Unintentional Consequences if you were to remove them.

The Function of Roots

Roots have two (2) basic functions – structure and feeding. Structure roots are those that start in at the base, growing under the canopy of the tree. As these roots move outward, they become smaller and smaller in diameter much like the structure of the limbs you see above. Their job is to provide a stable foundation. The feeder roots are small and fibrous and their job is to feed the tree, providing nutrients and water. So, you can see the distinct difference. Most people, when seeing roots, only see the structure roots, not the whole picture.

The Pruning of Roots

Remember the homeowner Nellie that wanted to go Lizzie Borden on the roots in her front yard? She doesn’t understand what potential consequences her actions may have on her tree. Here are just a few to consider –

  • Stability: The large roots that radiate out from the trunk support the tree. Cutting ones larger than 2″ in dia can put the tree at risk of falling over in high winds or inclement weather.
  • Diminished Vitalitu: Remember that roots are the ‘mouth’ of the tree. Cutting those roots reduce the amount of nutrients and water the tree can take in. Let’s call it Lap Band surgery, but in this case you don’t want to shrink the tree……. or do you? While younger trees have a greater ability to bounce back from root pruning, older trees have a harder time. Additionally, trees that are stressed from health or environment issues are at higher risk of mortality. Signs of stress in pre or post root pruning trees may include dead limbs in the crown, stunted growth, yellow or anemic foliage.
  • Pests and Diseases: Like the human body, trees that are in distress are easily susceptible to attack from pests and diseases. Many fungal infections will enter the cut roots, causing vascular issues that are very difficult to recover from. Stressed trees can also become Hometown Buffet for chewing/sucking insects like bores, scales and beetles.

Construction and Landscape Renovation

Adding onto the house for the out-laws? Installing a pool? Or just renovating your landscaping? These are another common area where roots have the potential to be cut and damaged. If you are installing a new irrigation system in your yard, try to incur minimal damage by installing irrigation like spokes on a wagon wheel as shown.

Remember this rule of thumb – a tree will put out a root system at least as wide as the drip line.

What do I need to know if I must prune roots in my yard?

First off, remember that root pruning should NOT be for aesthetic reasons only. If the roots are damaging walkways or foundations, that is a different issue. But remember what we’ve discussed – pruning roots can have a negative effect on the tree. In your desire to save the foundation you might have weakened the tree causing it to fall on your roof. Ouch! Reach out to your local arborist for his professional opinion.

Next, don’t cut roots larger than 2″ in diameter. The maximum one should consider removing in one procedure is 20% of above-ground roots. Again, remember the potential consequences.

Is there a better time of year to prune or remove roots? Yes. winter thru early spring is the best time, as that is when there is the least stress on the tree.

So, what do we take away from this. Yes, roots can be pruned with the knowledge of how/why they exist. They can also be pruned knowing what the potential outcome may be. If you are not sure, contact your local arborist for a consultation.

Tree roots growing on the ground surface create problems for many homeowners, especially in older neighborhoods where larger shade trees have been established for 15 to 20 years.

The roots make lawn mowing difficult. Equipment bounces over the rough surface, grass is often scalped and the root itself is damaged. There may be a safety hazard with riding mowers.

Any large growing tree, given sufficient time, will produce surface roots that can interfere with lawn care. Faster-growing trees tend to produce surface roots sooner than slower-growing types. Trees such as maple, poplar and willow should be avoided in areas where surface roots would be major problem.

Natural root growth contributes to the formation of surface roots on most plants. Most tree roots are formed four to eight inches below the soil surface. As the root continues to grow in length, it also increases in diameter, just as its above-ground counterpart, the trunk.

For example, a root formed four inches underground will be a surface root once it grows to a diameter of eight inches.

Soil erosion can also expose portions of the root system on some trees. Soil under trees that produce very dense shade tends to be subject to erosion because it is difficult to establish suitable stands of grass or ground to hold the soil in the place.

One way to deal with surface roots is to prune them, just as you would a problem branch or stem above ground. This is often the only solution (short of removing the tree) if the roots are damaging paved walks and driveways.

Cut cleanly with a sharp pruning saw to minimize the wound to the root. A good clean cut will heal quickly and be less likely to be invaded by decay.

Before you proceed to cut off all the problem surface roots under a shade tree, it is important to realize that such a procedure can permanently damage the tree. Most functioning roots of any tree are in the top foot of soil. Even shallow excavations, such as for sidewalk construction, can be extremely damaging to nearby trees.

Also, the root system is responsible for anchoring the tree and for absorbing water and nutrients that keep the tree alive.

A good rule to follow in root removal is to make certain that no more than a third of the roots under the tree’s drip line are removed at any one time. The larger the root, the more support it gives the tree. Once roots are cut, the tree has to be treated as if it had been transplanted — with increased fertilizer and water until the tree adjusts to the pruning stress.

An alternative and less damaging solution is to cover the surface roots with one to two inches of soil. Topsoil should be mixed with peat moss and sand to increase drainage and reduce the chance of the root system smothering

Beech trees, which always develop shallow roots, are about the only tree species that can be damaged by even a thin layer of soil over the root system, so surface roots under beech trees should be left alone.

An even better solution is to plant a ground cover. The ground cover is taller than grass and hides the surface roots. If the roots are in a pathway area, install stepping stones among the ground cover. Few ground covers are tolerant of foot traffic, and stepping stones will protect both tree roots and ground cover.

You can delay surface root growth by choosing the right tree. If you plan to plant a shade tree and want to maintain a good turf area underneath, consider one of the following: oak, ash, gingko, honey locust, sweet gum, Kentucky coffee tree, linden or black gum. Trees that have a smaller mature size create fewer surface root problems.

Finally, when no other alternative can be found, the offending tree itself can be replaced with a deeper-rooted type. This is often better than extensive root removal. Generally, most homeowners can learn to live with surface roots. Take corrective measures only when the problem becomes severe or threatens to damage walks, driveways or patios.

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There are a variety of things you can do to attract songbirds and other wildlife to your home.

Consider what wildlife needs, then ask yourself if your property meets those needs.

Two primary needs for birds are cover and food. Providing cover usually is more important than providing food.

Consider planting some shrubs and trees that will offer both food and cover for wildlife.

Get various sizes of shrubs and trees. Birds divide their habitat vertically. Some birds are found only in the shrub layer, while others prefer the tree tops.

Clumping trees and shrubs together also helps. A single tree or line of trees in the front yard won’t provide very good wildlife habitat. Planting islands of trees with shrubs underneath will give you the diversity required to attract a variety of birds.

Certain plants and trees are more attractive to wildlife than others. Big mast producers, such as hickories and oaks, are important to plant or maintain. They provide both food and shelter. Squirrels feed on the nuts and build leaf nests in the treetops, while birds nest on the large branches.

Smaller trees also are important. One is service berry, which blooms white flowers in the spring. In early summer, it produces an abundance of juicy berries which are eaten by songbirds, doves, grouse, small mammals and other wildlife.

Mountain ash has bright red berries in the fall, which will attract cedar waxwings. Dogwoods and viburnums also offer excellent food and cover for birds.

Homeowners may not be able to plant a big oak or hickory tree, but planting smaller shrubs can work wonders.

Plants such as forsythia provide important cover early in the spring as well as nest sites. Raspberries offer excellent habitat for birds and small mammals and a ready source of berries for homeowners.

Flowers also attract birds and wildlife. You can create a garden with plants that butterflies and hummingbirds like.

Bee balm and columbine will attract hummingbirds with their red flowers, while butterfly bush and butterfly weed will attract a variety of butterflies.

What Is Root Pruning: Learn About Root Pruning Trees And Shrubs

What is root pruning? It is the process of cutting back long roots to encourage a tree or shrub to form new roots closer to the trunk (common in potted plants too). Tree root pruning is an essential step when you are transplanting an established tree or shrub. If you want to learn about root pruning, read on.

What is Root Pruning?

When you are transplanting established trees and shrubs, it’s best to move them from one location to another with as many roots as possible. The roots and soil that travel with the tree or shrub make up the root ball.

Usually, a tree or bush planted in the ground will spread its roots far and wide. It would be impossible, in most cases, to try to include all of them in the plant’s root ball. Yet, gardeners know that the more roots that a tree has when it is transplanted, the faster and better it will adjust to its new location.

Pruning tree roots before planting reduces transplant shock when the moving day comes. Root pruning trees and shrubs is a process intended to replace the lengthy roots with roots closer to the trunk that can be included in the root ball.

Tree root pruning involves clipping the tree’s roots well about six months before the transplant. Pruning tree roots before planting gives new roots time to grow. The best time to trim roots of a tree or shrub to be transplanted depends on whether you are moving it in spring or in fall. Trees and shrubs destined for spring transplant should be root pruned in the autumn. Those to be transplanted in fall should be pruned in spring.

Root Pruning Trees and Shrubs

To begin root pruning, mark a circle on the soil around the tree or shrub to be transplanted. The size of the circle depends on the size of the tree, and should also be the outer dimensions of the root ball. The bigger the tree, the bigger the circle.

Once the circle is marked, tie up the lower branches of the tree or shrub with cord to be sure they are not damaged in the process. Then dig a trench in the ground along the outside of the circle. As you dig, keep each strata of soil in a separate pile.

Cut the roots you encounter with a sharp spade or shovel edge. When you have dug down sufficiently far to get the majority of the roots, fill the trench back in with the extracted soil. Replace it as it was, with the topsoil on top, then water well.

When transplant day comes, you re-dig the trench and extricate the root ball. You will find that pruning tree roots before planting caused many new feeder roots to grow within the root ball.

Transplanting established trees and shrubs can be risky because you will damage many of the feeder roots during the transplanting process. Feeder roots are responsible for absorbing the majority of essential nutrients and water. To minimize the shock to the plant, the Penn State University Extension educator Emelie Swackhamer recommends root pruning several months to one year in advance of the move, depending on the size and type of the plant.

Root pruning

Pruning the roots will encourage the plant to produce a flush of new feeder roots. The goal is to allow the plant to develop new feeder roots within the zone of the future root ball that will be moved. This will reduce the amount of transplant shock the plant experiences. Before root pruning you should consider the size of the root ball that will be moved. . The greater the root ball diameter, the more roots will be included in the move. Also remember that bigger root balls weigh more. Consider how the plant will be lifted and moved. Ball carts, wagons, tarps, or thick folded cardboard can be helpful in transporting the dug plant to its new location.

When to root prune depends on when you wish to move the plant. For most plants, root pruning is recommended in the fall, followed by transplanting in the spring. This allows the plant to grow new feeder roots in the pruned zone over the winter without the burden of supporting new growth. For larger plants, you may want to root prune one year or more before transplanting. Keep in mind larger plants will need more time to become established after transplanting. Alternatively, rooting pruning in the spring for a fall move is possible; however, the root pruned plant will need to be watered during summer dry spells. Be aware some plants do not respond well to being moved in the fall, especially those with thick and fleshy roots (e.g., Magnolia, tulip poplar, oaks, birch, rhododendrons, hemlocks, and flowering dogwood).

Methods for root pruning vary. One method called spading involves cutting through the existing roots with a spade, making a circular cut all the way around the plant. The edge of this cut should be just inside the edge of the future root ball. Spading works best for small plants or plants that have not been in the old site for a long time.

Another method called trenching involves digging a trench around the plant and refilling the trench where the new feeder roots with develop with soil high in organic matter. Trenching is more appropriate for plants that have been located in the old site for several years or more. Trenching techniques also vary, depending on plant size. Trenching can be done all the way around the plant or only part of the way around the plant, followed by further trenching later in the season. To root prune using trenching, dig a trench 8 to 12 inches wide or wider, 12 inches deeper or deeper with the outer edge of the trench corresponding to the outer edge of the future root ball. Next, fill the trench with soil high in organic matter, made by mixing two parts topsoil with one part compost. If conditions are good, the plant will grow new feeder roots in the trench of rich soil by transplanting time. These feeder roots will give the tree added ability to withstand transplant shock. Be sure to move as many of these new, young roots as you can when you move the plant. Before digging the root ball for transplanting, check to see if a good net of fibrous roots has developed. If few roots are found in the trench, you should consider postponing the move for another year. In addition, when you do decide to move the plant, digging a root ball larger than originally planned may assure that all of the new roots go with it.
Once the roots are pruned, special care should be taken to assure the root ball receives sufficient moisture, especially in the event of a dry fall or winter season. Check for soil moisture levels by feeling the soil. If the soil is dry two to three inches below the surface, give the tree a good soaking, assuring that the trench area is well watered. A two to three inch layer of mulch over the root ball but not in contact with the trunk or stems of the plant can help hold moisture in the soil and also protect the roots from cold temperatures during the winter.

Transplanting
Prior to moving the plant, prepare and dig the hole for the plant in the new location. Also soak the root ball of the plant before moving so that the soil will remain together during the digging process. Carefully dig the soil away from the root ball, and then wrap the whole ball in untreated natural burlap. Be very careful not to use synthetic burlap because it will not rot away and will eventually restrict the growth of the roots. Lash the burlap together securely to hold the roots firmly in place. You can do this by using a large upholstery needle and untreated natural twine to stitch the burlap tightly around the root ball.
Carefully move the plant using a cart, a rented ball cart, burlap, or cardboard. The goal is to keep the root ball intact. If the soil ball breaks, it will break the roots inside and may lead to the death of the plant. Make sure the plant is set at the same depth in the new hole and fill in around the root ball with topsoil. Mulch lightly with three to four inches of mulch, keeping the mulch off of the trunk or stems of the plant, and be sure to provide adequate water throughout the entire next growing season.

Source: Penn State University Extension

Edward F. Gilman
Journal of Proceeding of the Florida State Horticulture Society 100:397. 1987.

Lateral root pruning and root stock undercutting is practiced in field production nurseries. It is intended to produce a compact, fibrous root system, a higher root to shoot ratio and better transplant survival. However, root pruning is not uniformly practiced in Florida. Timing, depth and distance from the trunk vary widely among nurseries which root prune, and not all nurseries and tree movers practice root pruning.

Lateral roots formed in response to pruning reportedly originate close to the pruning cut. Therefore, it is hard to visualize a more compact root system developing unless roots are cut close to the trunk. Rootpruning Quercus virginiana 5 cm inside the root ball 1 year prior to harvest and then again 6 months before harvest at the edge of the harvestable root ball increased dry weight of fibrous roots inside the root ball six-fold compared to non-pruned plants. Root-pruning Picea pungens 20 cm inside the edge of the harvestable root ball 5 years before harvesting resulted in a 4-fold increase in root surface area in the root ball. Apparently, harvesting the ball beyond the point of root pruning can increase root density within the root ball.

Root pruning reduces above-ground plant size and may increase time to harvest a field-grown nursery crop. However, long-term growth is either unaffected or increased.

Number of new roots generated by root pruning varies among species. Platanus occidentalis generated an average of 32 new roots whereas Quercus virginiana and Ulmus parvifolia ‘Drake’ had less than 10. For five of the six species, 69% or more of the new roots originated within 2.5 cm of the cut. However, only 56% of new Acer roots originated within the zone. Acer had 27% of new roots more than 5 cm behind the cut; all other genera had 14% or less. Growth of existing lateral roots was stimulated by root pruning on five of six species tested.

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