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Archive for the ‘Root-washing’ Category

This year’s New England Grows featured a talk by Jim Flott, who discussed the bare-root transplanting of large trees.  Jim talked about root-washing, something he has studied, practiced, and taught, on his own and with the late Bonnie Appleton of Virginia Tech.  He spoke about the history of bare-root transplanting — until the middle of the 1900s bare-rooting was the primary way to transplant trees — and about bare-rooting with air tools.  It was a great presentation; this abstract by Flott and Appleton covers a lot of the territory Jim discussed, and it’s worth a read.

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Bare-root transplant with air tools — 12″ caliper London Plane tree, moved in late July 2009 in Wellesley, MA.

After Jim’s talk in one of the large auditoriums, he moved to a smaller room for an ‘Speaker Unplugged’ session, where people could ask him questions and exchange information.   As had happened at New England Grows three years ago, when Matt Foti discussed bare-root transplanting with air tools, someone asked about the effects of bare-root transplanting on a tree’s taproot.

How does bare-root transplant affect a taprooted tree?  The answer, both from Jim and from Matt, is that taproots are rarely an issue.

A taproot typically forms when a seed germinates; the baby taproot emerges first from the seed, growing down and anchoring the seed in the soil.  Next, the cotyledon shoot emerges and grows upward.  As the cotyledon starts to photosynthesize, root hairs branch out from the taproot, and the root volume grows and spreads.  The depth of roots is determined in part by available moisture and in part by soil type.  Typically, organic soils — which hold water and allow good cation exchange — rest at the top of the soil profile; mineral soils underlie the organic horizons, and are much less hospitable to roots.  Here in New England soils may be quite thin, and are often underlain with rock.

So taproots here will serve that useful anchoring function early in a tree’s life, but soil conditions and the plant’s own tendencies will promote the outward, rather than the downward growth of a tree.  In fact, the overall growth of tree roots tends to be outward, rather than down; the old image of a root mass volume and form mirroring a tree’s crown volume and form has been proven false.

We know that trees tend to develop their roots in the top 18″ of soil; the larger the tree, the deeper that zone may go, but typically it extends no more than 3 or 4 feet below grade.  Some thick roots on very large trees may extend vertically down in this zone, if soil conditions permit, but many more run horizontally away from the tree’s trunk.  The anchoring function of that original taproot, if it remains, is replaced by the anchoring provided by a much broader and more extensive mass of roots growing out and (to a much less extent) down.

As I wrote in an earlier post (with thanks to Linda Chalker-Scott for its title):

It’s helpful to keep in mind another factor when thinking about taproots and transplanting trees.  More often than not, a large tree being transplanted was planted out years earlier as a B&B plant, or possibly moved into place with a tree spade.  Both methods would have cut any taproot in the initial planting.  When the end of a root is cut, the tree tends to send shoots out from just above the cut end.  In a vertically oriented root, the new shoots are apt to extend horizontally from the cut end, and feeder roots would similarly extend out horizontally.  The situation may well be different for a tree that has grown from seed in one place, that someone now wants to transplant bare root, but for most landscape trees the taproot issue is moot — whatever taproot may have existed when the tree seed germinated has already been cut, and the tree has adjusted for its loss.


A carrot grows downward, with rootlets out to the side and foliage above ground. A tree is not a carrot. Photo by obenson in Flickr.

This beech tree was moved last fall, having been transplanted once about 20 years ago. See how the root mass extends far out horizontally, with a relatively shallow depth.

This is one of the thickest roots extending vertically from the beech’s trunk. This root was cut in the earlier (20 years previous) transplant; note the resultant root growth just above the cut.

 

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Last year I worked on a large mall planting project.  A number of trees had to be pulled out to make way for a new parking layout; the islands they had been growing in were removed and paved over, with new islands located in a different configuration.  Most of the trees were hauled away by the landscape contractor, but one ended up in a discard pile next to the mountain of loam that had been excavated for reuse.

I was interested in the root configuration on this six-inch caliper red maple.  A mass of fibrous roots wrapped closely around the tree’s trunk, much like cotton-candy filaments spun around a paper cone.  Looking at it more closely, I found that the fibrous roots grew out of thicker woody roots, some of which had been cut during the tree’s original ball-and-burlapping, and some of which, growing since that operation, were circling the trunk.  Take a look:

Fibrous roots circling the six-inch red maple trunk.

Pulled away from the trunk, the roots clearly are circling it. Over time, as the tree grew in girth, these roots likely would have constricted the flow of nutrients between root mass and crown

This sort of circling root is usually seen when the soil mass in a B&B root ball is of different porosity from the soil surrounding it; moisture will not move from one soil mass to the other until one mass is completely saturated.  Because roots tend to grow where moisture and oxygen are available, they will often stay within the root ball, and circle around the trunk as they grow.  The problem is made worse when burlap is not pulled away from the ball, as the burlap constitutes yet another interface for the moisture to move through.

Here's the tree's underside. Note the girdling root snaking on top of the big torn root facing the camera, and the curiously self-contained look of this root mass. The tree's problems likely began early in its life.

Not every B&B tree has these problems, and in those that do, not every rooting problem can be remedied at planting time.  Judicious treatment — looking for circling roots that can become girdling roots, cutting back girdling roots and cutting or redirecting circling roots, roughing up the sides of the root ball, removing or cutting down wire baskets, pulling down or removing burlap — can go a long way in helping B&B trees establish better in the landscape, and in remedying problems that threaten a tree’s long-term health and viability.  For more discussion on root issues affecting B&B trees, check out this post on Matt Foti’s station at the MAA’s Elm Bank bare-root workshop in September 2009.

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Another question asked at last week’s New England Grows about bare-root transplanting was “How do you make sure the roots don’t dry out?” The answer, of course, is that you water the tree you’re moving.  You water it thoroughly a couple of days before the transplant, to insure that the tree’s tissues have good turgor pressure and moisture reserves for the bare-rooting.  You take a break every now and again during the blow-out (if you’re using compressed air) and spray down the exposed roots with water.  You may spray more water on the roots — the top, bottom, and inside of the root mass — when you pick the tree up on forks to deliver it to its new home.  You ‘mud in’ the tree as you backfill, saturating the backfill soil with water to eliminate any air pockets and again, to combat root dessication.   And once you have mulched the tree well, you water still more.

Water in all phases of the operation is key to tree transplanting.

Cornell’s Urban Horticulture Institute advocates using a hydrogel slurry to hold water on the bare roots during planting.  Their excellent Creating the Urban Forest:  The Bare-Root Method describes the process of planting young trees bare-root, and is well worth reading.  The challenge of using a slurry for large-tree transplanting would be in getting a consistent coating of hydrogel on the roots (you can’t dip the root plate in a tub, the way you can with a sapling root mass) — but there must be a solution (so to speak) to that problem. And finally, aftercare is critical.  Moving a large specimen tree bare-root takes time and effort, and it would be folly to follow all the steps, get the tree in the ground, and then leave its re-establishment and survival up to chance.  Some arborists add fertilizer and bio-stimulants to the backfill, some don’t.  What is essential, again, is water.  Consistent and adequate water for the first growing season is the best way to make sure that a transplanted tree makes the transition to its new home, survives, and thrives.

Watering in a root-washed pin oak at Cavicchio's Nursery. Photo courtesy of Carl Cathcart.

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In the fall of 2008 Carl Cathcart persuaded Cavicchio’s Greenhouses to wash the roots on a stressed B&B Quercus rubra (Red Oak), and to plant it in a spot where it might be able to settle in.  Carl sent me photos of the root-washing process, which I posted on Taking Place last summer.  He and I then drove to Sudbury to see the tree, and to check out the three Red Oaks in similar condition that Cavicchio’s had planted conventionally, to see how they would progress in relation to the root-washed oak.

Photos of all the planted-out trees are on Taking Place, and because there are so many of them I’m simply posting the links to those posts here.  To see the photos and read about the root-washing experiment, click here first, and then click here.

The summary:  in mid-July, the bare-rooted tree looked best of all four trees.  It had some dead wood, but nothing that hadn’t been on the tree the previous autumn, and it had good foliage color and density, if the foliage itself was a bit small.  By comparison, the other three trees looked as if they were struggling: each tree had sprouted out new shoots along its trunk, often a sign of a tree in decline; foliage was small, and there was lots of deadwood in each tree.  It’s not a scientifically rigorous experiment, but one worth following over the next few years, to see how the trees progress.

Leaning into the root ball.  Lower water pressure may be a bit easier for those tiny feeder roots, but high pressure makes getting the hard clay soil off a faster process.  It's not clear yet how feeder root regrowth is affected by this kind of treatment, whether the pressure comes from air or water.  Early reactions seem promising, but it may be several years before a re-examination of the roots shows how risks and benefits balance..

Leaning into the root ball. Lower water pressure may be a bit easier for those tiny feeder roots, but high pressure makes getting the hard clay soil off a faster process. It's not clear yet how feeder root regrowth is affected by this kind of treatment, whether the pressure comes from air or water. Early reactions seem promising, but it may be several years before a re-examination of the roots shows how risks and benefits balance..

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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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