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Posts Tagged ‘secondary roots’

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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Dave Leonard from Lexington, KY, manned the root forensics station at the September 10 MAA air-tool workshop at Elm Bank.  He used an Air Knife to excavate the root ball of a 4″ caliper red maple that was showing signs of decline.

Turf provided the only competition for this tree, but it was showing dieback and early fall color at the MAA workshop.

Turf provided the only competition for this tree, but it was showing dieback and early fall color at the MAA workshop. Dave Leonard excavated at its base to take a look at its rooting habit for possible problems.

With soil blown away from the original root ball, it was clear that the tree’s planting had initiated some problems — parts of the wire basket appeared at the edges of the root ball, and cut root ends had sent out an explosion of fibrous roots that turned back toward the trunk.

Root ends cut during the tree's digging in the nursery sent out masses of fibrous roots, quite a few of which turned back toward the trunk.  The interface between root ball soil and surrounding soil can inhibit root growth into the surrounding soil; removing burlap, removing the wire basket, and breaking up the root ball soil, particularly at the ball's perimeter, can help promote the spread of new roots.

Root ends cut during the tree's digging in the nursery sent out masses of fibrous roots, quite a few of which turned back toward the trunk. The interface between root ball soil and surrounding soil can inhibit root growth into the surrounding soil; removing burlap, removing the wire basket, and breaking up the root ball soil, particularly at the ball's perimeter, can help promote the spread of new roots. Note the soil line some inches up the trunk flare; removing soil above the trunk flare will also benefit the tree and lessen its stress.

Dave cut away the roots that he could not redirect outward, and trimmed off the roots that had begun to circle the trunk flare’s base, which would otherwise eventually girdle the trunk and major anchor roots.  Some of these roots were the beginnings of a secondary root system put out by the tree in response to its stress.

Removing the worst of the inward-growing and circling roots improves the tree's chances for survival.

Removing the worst of the inward-growing and circling roots improves the tree's chances for survival.

After excavating the root ball, Dave intended to continue to blow soil out away from the root ball, creating a shallow crater  out at least to the tree’s dripline.  Removing turf from that zone would eliminate plant competition for soil moisture; the addition of 2-4″ of mulch (kept away from the trunk) would help the soil retain moisture and an even temperature, add organics to it over time, and lessen the chance of soil compaction that inhibits soil/air gas exchange.

Dave said that he would also consider lifting the tree a few inches, to bring its trunk flare into a better relationship with surrounding grade.  This tree had been in the ground for a couple of years; Dave suggested that tree lifting might be worth doing within two to four years of planting, but could be detrimental to the tree after that.  (The window of opportunity for lifting a tree would be a lot wider if an air tool were used, rather than a Bobcat or excavator, as the tree could be bare-rooted and set back in place with relatively little stress from the process.)

Demonstrating arborist at this station:

Dave Leonard, Dave Leonard Consulting Arborist, Inc., Lexington, KY

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At the MAA Elm Bank workshop on September 10, 2009, Matt Foti demonstrated how to address root problems at the time of planting.  He had a fairly large collection of trunk-and-root masses to illustrate his points, and used them to show how girdling roots, secondary root systems, and J-rooted systems can develop as a result of poor planting or growing practices.

Matt first showed a couple of forest saplings he had pulled early in the day to illustrate how a naturally-seeded tree’s roots grow.  The sapling’s roots were evenly spaced around its stem, and extended out a distance relatively equivalent to the distance its topgrowth extended from the stem.

This little forest-grown white pine has a clean, evenly spaced root system.

This little forest-grown white pine has a clean, evenly spaced root system.

He then pointed to a couple of nursery-grown trees whose rooting problems had become evident after several years.

These root systems have been cut in the digging process.  In an attempt to regrow roots, the foreground tree has sent out a secondary root system, several of which are beginning to girdle other roots.  Kept too long in a burlapped ball or in a container, roots will often turn back in to the ball, making effective planting and long-term growth problematic.

These root systems have been cut in the digging process. In an attempt to regrow roots, the foreground tree has sent out a secondary root system, several of which are beginning to girdle other roots. Kept too long in a burlapped ball or in a container, roots will often turn back in to the ball, making effective planting and long-term growth problematic.

Shrubs as well as trees are susceptible to root problems; Matt dismantled an Ilex verticillata root mass to illustrate how he treats roots bound in a container or in burlap before planting.

Fibrous roots hold together in a near solid mass right out of the container.

Fibrous roots hold together in a near solid mass right out of the container.

Using a three-pronged fork to untangle the root mass.  For a bigger shrub or small tree, a machete or pitchfork may work well to loosen soil and reorient roots.

Using a three-pronged fork to untangle the root mass. For a bigger shrub or small tree, a machete or pitchfork may work well to loosen soil and reorient roots.

Ilex verticillata root mass, now ready for planting.

Ilex verticillata root mass, now ready for planting.

Soil can present another problem for nursery-dug B&B trees.  Clay soils make sturdy root balls, which can be useful for shipping, but not so great for root growth.

This pair of trees have root masses encased in rock-hard clay soils.  Note the solid clumps of clay in the foreground, and root growth only on top of the root ball -- these roots found it impossible to grow into and through this soil.  Breaking up the soil in a root ball like this before planting promotes the tree's future health; leaving this kind of root ball intact almost guarantees tree stress and decline.

This pair of trees have root masses encased in rock-hard clay soils. Note the solid clumps of clay in the foreground, and root growth only on top of the root ball -- these roots found it impossible to grow into and through this soil. Breaking up the soil in a root ball like this before planting promotes the tree's future health; leaving this kind of root ball intact almost guarantees tree stress and decline.

Closeup of rock-hard clay root ball, broken apart (fairly violently) for demonstration purposes.

Closeup of rock-hard clay root ball, broken apart (fairly violently) for demonstration purposes.

Another example of a dense clay root ball that constricted root growth to the tree's great detriment.  Soil had also been piled up around this tree's trunk flare, further challenging its ability to live.  Tough conditions for a tree to grow in.

Another example of a dense clay root ball that constricted root growth to the tree's great detriment. Soil had also been piled up around this tree's trunk flare, further challenging its ability to live. Tough conditions for a tree to grow in...

The point of these illustrations was to show how necessary it is, when planting a tree or shrub, to work with the root ball before covering it with soil.  Removing wire baskets, removing burlap, loosening or removing the soil, untangling roots as best as possible, pruning roots when necessary — all these tactics make up a strategy for promoting real tree growth.  Bare-root techniques have shown that a great deal of the work that arborists do these days is remedial — that is, is work intended to remedy poor growing, digging, or planting practices.  With the knowledge arborists now have of how root issues so obviously affect plant health, it only makes sense to attend to those issues early on, to avoid greater problems later.

Demonstrating arborist at this station:

Matt Foti, Matthew R. Foti Landscape and Tree Service, Inc., Lexington, MA

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