Posts Tagged ‘Plant management’

Say you’re a growing country club in a nicely-treed community, and you need to enlarge your parking lot. And perhaps you want to lower its grade. The lot has some mature oak trees in it, and they add a certain je ne sais quoi to the scene, so you decide to save the trees by keeping the grade as is around the base of their trunks. You retain the roots and soil with a mortared stone wall. Voila!

Good idea – but woops! The minimum standard for root preservation is to keep 10 inches of root mass diameter per caliper inch of tree. For these trees, that would spell at least 360-inch diameter root masses. Because the trees are so close together, their roots overlap significantly — but still, 360 inches is thirty feet of diameter.

This 18-footish enclosure takes a tad too much root; the country club will almost certainly be watching these trees decline and die over the next few years (and they may well drop dead branches onto the parking lot, or cars in it, in the process).

The idea of saving a mature tree is a good one, as long as the tree’s actual requirements for continued healthy life are met.   Now that we have the tools to see how large a tree’s root mass really is, it’s much easier to see how big the unimpeded area around it has to be for the tree to survive happily and to thrive.

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To continue yesterday’s post on the bare-root transplanting of a Norway spruce at the Perkins School for the Blind in Watertown, MA:

The crew uses a heavy canvas strap wrapped securely (more than once) around the trunk, and pads the Bobcat fork bracket. This tree's flat back meant it could be pulled securely up onto the forks without tying up branches; other trees would need to be tied up for easier spading and transport. Here, the forks are poised to push under the root ball, just below the wire basket.

Rolando prunes thin fibrous roots from under the basket, to release the root ball from the ground. Most of the root mass has already been blown out.

Spruce on the move. With almost all the soil blown off the root mass, it is light enough for the Bobcat to carry the tree easily across campus. Canvas straps secure the tree to the Bobcat; Rolando rides along just in case.

Closeup of the root mass. Virtually all of the roots on this tree were quite thin, and they made a dense mat that extended about nine feet out from the tree's trunk on several sides.

Mynor had dug out the hole with the Bobcat while Sonia and Rolando blew out the soil from around the tree. This site, next to a busy campus parking lot, challenged the crew to place the tree carefully. Cars were parked just to the right of the orange barrier in this photo, and other relocated trees ringed the dish on two other sides, so maneuvering to get the tree in place was a bit tricky. It's relatively easy to spin at least a small B&B tree to the right orientation; turning an air-spaded tree requires a bit more forethought. In this situation, a bit of three-dimensional visualization was necessary to be sure that the flat side faced away from the parking lot.

Sonia and Rolando used a rake handle and tape measure to determine the root mass's depth before adjusting soil depth in the new hole.

Additional native soil is added and compacted to make a pad under the trunk. When in doubt, it's better to place the tree slightly higher in its new location than to risk it settling deeper once it has been backfilled and watered in; tamping the soil firmly under and around the roots right at the tree's base helps insure both that the soil won't subside and that air pockets are eliminated.

Rolando guides Mynor in setting the tree in the right spot. Good communication is key through this entire project, and these guys were excellent in coordinating their work with each other.

Rolando and Santo shovel native soil under the rolled-up root mat, to secure and level the tree before its roots get spread out.

Sonia and Rolando spread soil under and over the roots as they unroll them from the bundle. Note that they are using soil excavated from the site, with no amendments. Bare-root transplanting eliminates the difficulties associated with moisture transfer between two types of soil (root ball soil and soil outside the root ball), which makes establishment in its new site less stressful for the tree.

With backfilling complete, the crew builds a berm.

With the berm in place, Sonia waters the backfill thoroughly. Some crews shovel in the backfill and water simultaneously, "mudding in" the tree for extra stability and the complete elimination of air pockets. Mulch will go on this new planting next, and then more water. Note that you can see the root flare, now that the tree has been excavated from its original root ball and planted at the proper depth.

Project site:  The Perkins School for the Blind, Watertown, MA

Project manager:  Sonia Baerhuk

Project crew:  Rolando Ortega, Mynor Tobar, Santo Masciari

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The Massachusetts Arborists Assocation bare-root workshops — one in August 2008, and one in August 2009 — have been spreading word through the Commonwealth about the benefits of air-tool tree transplanting, and word is travelling throughout Massachusetts horticulture circles now.

A couple of weeks ago I was chatting with Kristen DeSouza, one of the horticulturists at the New England Wild Flower Society‘s Garden In The Woods, and she mentioned that she had passed my name along to Sonia Baerhuk, who tends the grounds at Watertown’s Perkins School for the Blind.  Kristen told me that Sonia and her crew have been using air tools to  transplant trees on the school’s grounds for the last several months, and suggested that I get in touch with her.

And so last Thursday, a couple of emails and a phone call later, I pulled in to the visitor’s parking area at the Perkins School.  Sonia soon arrived in one of the grounds department’s Gators.  She very kindly showed me around the campus, explaining that a new and large building project had required the removal of dozens of large trees.

It’s a scenario typical of many institutional sites:  a program outgrows its home, the phasing of a master plan leads to a shifting of facilities or the construction of a new building, and the vegetation on site must either be removed or relocated.  Having worked at Perkins for several years, Sonia was no stranger to this course, of events, but still, she had been dismayed to see so many large specimen trees being cut and fed into the chipper.

Though the grounds crew does most of its own tree work, over the years they have called in arborists for their expertise, and Sonia knew and trusted Matt Foti’s expertise.  Matt had told her about the air-tool method, and on the strength of his recommendation, she signed up for the MAA’s Elm Bank bare-root workshop this past August.  At it, she absorbed as much information as possible.  She came away from the day’s event convinced that air-tool excavation and transplant was the best way for her crew to relocate any salvageable campus trees.

So Sonia and her boss Rich Falzone equipped the crew with an Air Spade and an Air Knife, coveralls, eye protection, ear protection, and respirators, and began to direct the relocation of trees.

To date, the Perkins crew — Sonia Baerhuk, Rolando Ortega, Mynor Tobar, and Santo Masciari — has moved several 15-20′ Norway spruce, a fastigiate white pine, a Forest Pansy redbud, several apples, and a beautifully structured 25-30′ tall Halesia.

On the day I visited, they were ready to move another Norway spruce from a location that is slated to become a pondside patio.  Its new home would be a lawn next to a parking lot to which they had already moved a number of evergreens.  The new planting is beginning to screen the lot from adjacent buildings; over time, this grove will shade the parking lot and the walkway near it.

Sonia Baerhuk marking the new home of a 15' Norway spruce to be relocated.

Fifteen-foot Norway spruce in its original location next to the campus pond. The crew discovered that the Norway's roots were interwoven with roots from other nearby trees. This tree was flat on the side facing the fence.

Currently, the grounds crew rents compressors. These two generated air for an Air Knife and an Air Spade. Note the plywood barriers set up to prevent soil overspray onto the lawn. In this project, the crew did not dig a trench to hold blown-out soil; they simply started blowing soil out from the trunk and followed the roots out to and beyond the dripline.

Sonia and Rolando, kitted out in their PSE: coveralls, gloves, hats and hoods, ear protection, eye protection, and respirators.

Blowing soil off the roots took about three hours. Sonia likes to divide the root mass diameter into quadrants and work systematically, while Rolando prefers to work all around the tree; when they work in tandem they use whichever method fits the site conditions best.

Edges of the original B&B root ball are barely visible here; it was roughly 24-30" across. Rolando and Sonia discovered the wire basket still around it. They also discovered that the root flare sat several inches down in the original root ball.

The spruce was anchored with a thick mat of fibrous roots; the crew found virtually no roots larger than 1/2" in diameter. Here, they are pruning root ends under the eighteen-inch deep mat.

Still pruning the mat, and rolling it up toward the trunk to blow soil out from under the tree.

The root mat rolled up and bound in burlap for further blowing-out and moving.

Project site:  The Perkins School for the Blind, Watertown, MA

Project manager:  Sonia Baerhuk

Project crew:  Rolando Ortega, Mynor Tobar, Santo Masciari

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Mike Furgal sent me photos of an 8″ caliper Weeping White Pine  that he moved a couple of weeks ago, remarking that this tree, though relatively small, was the most challenging tree he’s moved bare-root.

The tree was situated in a small berm next to a house and a driveway, and shared the bed with a 7′ Hinoki Cypress and an 8′ Blue Holly.  Mike blew soil out of the entire bed to move all three plants, whose roots were interwoven.

Pine roots running toward the house and drive extended no more than three feet. Roots running under the lawn told a different story; the two main roots that Mike found were 16-18 feet in length; they had plenty of moisture available and plenty of rooting room to grow.

Mike began work on the bed by blowing soil at the tree’s dripline and at its root collar, to assess where the roots were.  He found that they ran along the edge of the bed until they hit the house; from that point they grew out into the lawn.

Here are his photos:

beginning location 2

Rooting space is constrained by the berm's proximity to the house and the driveway.

begining location 3

Ample lawn space gives plenty of rooting opportunity in other directions.

beginning location 1

Lots of roots here -- note how they run along what had been the bed edge, and extend back toward the house. Once they hit the house, they then ran out into the lawn.


Here's what the excavated bed looked like, with Hinoki Cypress, Blue Holly, and Weeping White Pine roots woven together.

veron pine diggiing

Tremendous root extension can be kept with air-tool excavating, and while not all fine roots remain, a significant number of them do.

veron white pine digging 2

The Pine ready for its move. These lawn-side roots are sixteen to eighteen feet long. Compare that root length to the accepted standard size of a B&B root ball, which allows ten inches of root-mass diameter for one inch of trunk caliper. For an apples to apples comparison, if we include the three feet of root on the tree's other side, this tree has 19 to 21 feet of root extension, as opposed to the 6-foot, 8-inch root mass diameter you would see on a B&B specimen.

veron white pine digging 3

Moving the excavated pine was the trickiest part. Mike and his helper used a Bobcat and a Dingo -- tricky to coordinate both machines at once.

veron moving 3

Closeup of the two monster roots extending away from the house and drive.

veron moving 1

Anyone else reminded of a bride with a really long train? One major difference: a bride doesn't require this kind of machinery to move around.

veron moving 2

The pine moving to its new home on the other side of the house.

I’ll post photos of the tree in its new location shortly.

Arborist:  Mike Furgal, Furgal Tree and Landscape, Northborough, MA

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If you’ve been interested in the issues on this blog, you might well want to look into another blog, this one written by four horticulture professors.  They’re each based somewhere different — Washington State, Virginia, Michigan, and Minnesota — and they write with humor and expertise about plants and plant issues.  The Garden Professors started posting in July 2009.  They talk about root-washing, propagation, nursery practices, soil contaminants, slugs, rubber mulch — you name it, they’re addressing it.  A recent post highlighted the air-tool transplant of a beautiful 10″ caliper weeping white pine by a Michigan State University Nursery Management class and the MSU arborist. — take a look for some good pix and clear, personable, often funny writing about a great range of up-to-the-minute plant issues.

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I was shuffling through some photos today, hunting for an illustration of girdling roots, thinking that I’d use one of a myriad of pix I have of subgrade snarlups.  But this picture popped up, and it seemed useful to show how a root that seems insignificant in infancy can grow to have an adverse effect on the health of the tree from which it springs.

These two girdling roots started out as thin, wirelike strands growing past the trunk of a sapling.

These two girdling roots started out as thin, wirelike strands growing past the trunk of a sapling.

This tree is a Norway maple in our backyard  (yes, we still have a couple of them).  From its position in the lawn I’m betting that someone planted it.  At the time of planting, it would have been a small tree — perhaps a 5-foot sapling dug from the yard’s border and moved to the lawn, or maybe one of the 1.5″ caliper whips given away by our town one year.

If you envision the young transplant then, you’ll imagine those two girdling roots as a couple of very thin, quite insignificant-looking roots, running parallel to and about two feet away from the trunk of that skinny tree.  They might have been considered circling roots, they might simply have just gotten twisted the wrong way in planting and continued to grow straight past the trunk.

As the tree grew in height it also grew in girth; the crown branched out, the trunk got thicker.  As the trunk got thicker, the roots and branches thickened.  A harmless condition in the tree’s juvenile days has turned into a bit of a problem in its middle age.  Now the skinny roots have fattened up, and have begun to squeeze the vascular tissue in the roots runny radially out from the trunk.  Bark above the girdling roots is traumatized (and not just by the squirrels that run up and down every morning) by constriction.  There’s a bit of dieback in the crown this year — though that may have been caused by something else (winter breakage invaded by fungus? Norway maple cussedness?)

The solution?  Chiseling the girdling roots away from the constricted roots to free up that vascular system could help, though at this stage it would be interesting to see if that section of root and trunk flare could really recover.  I have been using the Norway maples in the yard — the two mature ones, and a small thicket of saplings — as a small laboratory, so will keep watching to see what happens here.  Feel free to comment below….

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I was recently on Newbury Street in Boston. Turning away from the nifty pay-for-parking machine (these things have replaced meters on the street, and they couldn’t be more convenient, or more helpful for reducing street furniture clutter), I spotted this valiant little Gleditsia, working hard to stay alive:

What had been a typical street tree -- a standard-form Honey Locust -- was cut down at some point, and now sports shrub-like topgrowth.

What had been a typical street tree -- a standard-form Honey Locust -- was cut down at some point, and now sports shrub-like topgrowth.

A little way down the street was another Gleditsia, this one growing in a similarly sized tree pit, but intact from the saw:

Both trees work hard under severe limitations.  The far tree shows what the nearer tree could have looked like.

Both trees work hard under severe limitations. The far tree shows what the nearer tree could have looked like.

How well these characters are doing is a direct consequence of how well they’re being cared for, and of their native vitality. The far tree is impressive for its growth despite the tiny volume of root space available for it; the near tree admirable for its persistence.

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As you may know, this blog started as a series of posts on our other blog, Taking Place.  I branched it off that blog to avoid unbalancing the whole endeavor, and began posting on woody plant issues here.  I am currently working on copying older posts from Taking Place over to this blog as well (they’ll remain at Taking Place, too, as they are important there) — but it’s taking me a while.

So — if you want to read older posts on bare-root transplanting (root-washing and air-tool excavation), or on woody plants in design and woody plant management, you’ll be able to read current (from August onward) posts here, but will have to wait a bit for the older ones to arrive on this site.  If you just can’t wait, though, you can see all my pre-Taking Place In The Trees woody plants posts by clicking on the highlighted name — Taking Place — in the first paragraph.  That blog will then pop up.

Once that happens, scroll down and click on ‘Plants’ in the Categories list to the right of the page; doing so will make the list of tree and shrub posts pop up.  Scan through the list, and click on whatever title interests you to bring up the whole post, including some excellent photos.

And if you like what you see and read, take a look at the rest of the Taking Place site — there are some dandy photos and lots of observations on landscape architecture, design, and how we live in the green world.

Cute little dwarf liquidambar, freed from its container and soil washed away with the hose, ready to have its circling roots unwound, spread radially (as best as possible), and planted.

Cute little 'Gumball' dwarf Liquidambar, freed from its container and soil washed away with the hose, ready to have its circling roots unwound, spread radially (as best as possible), and planted.

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One reader wrote in with this comment to my last post: “It would be no good to specify bare root unless you were thoroughly acquainted with the land – soil, ledge, utility lines, for example – and spreading roots of other trees.”

And my answer, because there’s a lot to it:

Actually, bare root is good just for the reasons you enumerate; it’s much easier to plant roots alone than it is to plant a big slug of soil encasing a plant’s roots. And landscape architects, contractors, and arborists have ways of dealing with the issues you mention.

Contractors are required to call Dig Safe (http://www.digsafe.com/) to locate underground utilities on site before any excavation begins. The mis-location of utilities has been known to happen, but excavators are (ideally) careful about how they dig and about stopping when they hit something. Accidents can and do happen, but safeguards have been worked out to minimize their occurrence. (We had a little excitement at last week’s transplanting site over a gas line — apparently DigSafe found one gas line and marked it, but didn’t realize there was another several feet away. The mini-excavator found it — without breaking it — and DigSafe was called out to mark its course immediately.)

Irrigation lines, visible in some of the photos from last week’s posts, are considered expendable/fixable during a construction project. They are relatively flimsy and they run everywhere under many projects, so it is understood that they may be broken (even a shovel can break one), and will be fixed after construction and planting have been completed.

Bare-rooting a tree or shrub for planting — regardless of the surrounding soil type — often is better for the plant than planting it in a soil root ball. When one type of soil is introduced to another, as when a clayey soil root ball is placed in a sand/loam soil, the interface between those two types of soil resists the movement of water from one to the other. That means that if a clay root ball gets watered in thoroughly, water may not move so readily into the sandy loam. What incentive does the root mass have to move beyond that interface and thus into the sandy loam? Not much.

Opening up a root ball and mixing some of its clay with the surrounding soil in the wall of the hole will help, but still — with a bare-root plant that issue is a non-issue. Even with a poor soil, it’s easy to mix some planting loam in with the surrounding soil (again, you want to mix, not simply dump a pile that will give you that same resistant interface) and plant the bare-root tree or shrub in the mix; doing so will make it possible for the plant’s roots to reach as far as they have to for the moisture they need.

it is a tendency, unfortunately, of many planting crews (especially on very large jobs where speed is of the essence and there may be little job training for laborers) simply to push the burlap on a root ball down just below the surface, or in some instances to leave it tied in place before backfilling. Natural burlap eventually will rot, but it can take years, especially given the subsurface soil environment, where the burlap is protected from the atmospheric oxygen and UV light that breaks it down so readily in the nursery. In the meantime, that burlap constrains root extension into the surrounding soil, and can contribute to the roots turning back in to the root ball, which affects the growth of the whole tree. So — another reason bare-root is a good approach: no burlap to fool around with and to constrain root growth.

As for ledge: You’re unlikely to know the location and profile of subsurface ledge until you start digging. That’s just the way it is. Again, though, the presence of high ledge (that is, ledge just below the soil surface) argues for using a bare-root planting method. Since tree roots typically live in the top 12″ of soil (sometimes 18″, and sometimes deeper, given the plant genus and the depth of good soil), and tree root balls can be as deep as 36″, planting a tree with soil around its roots means that you have to accommodate that root ball. Sometimes you can slice off its bottom with little ill effect on the roots. Sometimes you can’t. With a bare-root plant, you don’t have to jimmy around so much with adjusting the height of the root ball.

Certainly, you’ll have to be sure you have adequate soil depth to plant the roots themselves (spreading them out radially, as they typically need to grow), but bare-root planting gives you much more flexibility in this regard.

OK. That’s it for this post, because I have to hit today’s design deadline, and this was a digression from working on it. Sorry about the lack of photos on this post; next one will have a set of really good ones, courtesy of Matt Foti.

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Tom Ryan*, my first landscape architecture mentor, and I have discussed the desirability of specifying that the trees and shrubs we design into a site be planted bare root whenever possible.   As long as the roots can be kept moist — something now entirely possible with the use of hydrogels — most nursery-grown plants fare better, are more apt to be planted in a way that promotes their future health, and are less expensive than B&B plants. And we all know that healthier plants mean more long-lived designs….

Nina Bassuk and the Urban Horticulture Institute at Cornell have put up on the web an outstanding illustrated tutorial on how to plant shrubs and trees bare root.

One of the challenges for landscape architects is to get more nurseries to offer bare-root plants for sale. Currently, balled-and-burlapped and container-grown are the most available kinds of woody plants in the nursery-to-contractor trade. Like any business, nurseries respond to demand.

Years ago, I was having a casual chat with the president of a local nursery and garden center, and asking why plant selections were limited to a number of fairly standard species and cultivars (I had recently assembled a plant list that specified some more unusual species than his large nursery carried). He told me that his nursery responded to demand; without greater demand for more variety, his business stuck with the standard choices. If more contractors were to bring him more complex lists, his nursery would be happy to accommodate them. It’s a bit of a chicken and egg argument — but essentially it means that continued and persistent demand will get results.

If landscape architects, through our planting choices and plant specifications, possess the ability to influence nursery offerings, then why shouldn’t we also be able to influence the method with which those offerings are packaged? With a greater understanding of the benefits of bare-root plants, perhaps more of us will start to specify bare-root plants, and so create the demand for nurseries to meet. It’s an idea worth exploring.

If you have had experience specifying bare-root plants for a project, we’d love it if you would write in and tell us about it.

Chionanthus retusus, Swan Point Cemetery

Chionanthus retusus, Swan Point Cemetery

*This September Tom will be named a Fellow of the American Society of Landscape Architects — a great honor for any landscape architect, and one that he fully deserves.

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