When all else fails…

As someone who has had a foot in Horticulture and a foot in Forestry throughout most of my career, people often ask me to compare the two disciplines.  One of the truisms that applies in both cases is, “When all else fails, blame the nursery.”  I’ve seen this following seedling die-offs in industrial forest plantations and I’ve seen it many, many times after street tree or landscape planting failures.  In fact, if you believe some people, tree nurseries are responsible for every plague and pestilence to ever afflict mankind.  Are some tree failures related to things that happened in the nursery?  Of course.  But there are lots of things that can go wrong between a nursery and a tree’s final destination; and even more things that can go wrong after it’s planted.

I know a lot of people don’t believe this, but nursery growers want their trees to survive and grow well after they leave their care.   Growing trees is like making cars and any other business.  You need satisfied customers if you expect to have repeat business.  The best growers are always looking at their production practices for ways to improve their product.  Last week I visited Korson’s tree farm in central Michigan.  Korson’s grows Christmas trees and B & B landscape conifers.   Rex Korson, the owner, has been concerned over the impact of root loss during transplanting of landscape trees.  So much so, in fact, that he is conducting his own trial on root pruning.

For those that are not familiar, root pruning of B & B trees is usually done a couple years before harvest by using a tree spade to severe tree roots.  The spade used for pruning is slightly smaller than the one used for harvest, so that new roots stimulated by pruning are harvested with the root ball.  Does it work?  I did a root pruning trial a few years back to see if it could improve survival of fall-planted oaks and had mixed results.  For Rex’s trees, however, the initial results were pretty impressive.  In the first photo below are root systems of Norway spruce trees dug with a 30” tree spade.  The second photo shows the root systems of trees dug with the 30” spade that had been root-pruned last October with a 24” tree spade.  The response in one-year’s time was dramatic.  At this point there no out-planting data but, other factors being equal, increasing the amount of roots harvested with the tree should increase transplant success.

I should hasten to point out that Rex is not alone.  I work with many other growers in the state that are constantly tinkering with this or that in their production systems; sometimes on their own, sometimes with university specialists or extension educators.  I’m not so Pollyanna to think that everything is always rosy in the nursery world but most growers, especially the better ones, are aware of the issues out there and are working to build a better tree.

Spruce dug with 30″ spade without root pruning

Norway spruce root-pruned in Oct 2011 with a 24″ spade and dug Oct 2012 with a 30″ spade.


Close up of new fine roots


Tree spade mounted on excavator for root pruning.  With this system an operator can root prune 8 trees in 5 minutes.

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Why it’s important to prune tree roots before planting

This week I discovered that one of our center’s landscape trees is ready to bite the dust. I was sad – but also happy.  It’s a wonderful teaching moment and if the tree has to give up its life to save others, I guess that’s okay.

As the video will show you, this Japanese maple was planted some years ago with a root circling the trunk.  As both the trunk and root have developed in girth, we’ve reached a point where the trunk is constricted and the weight of the tree is splitting this V-shaped specimen down the middle just like a turkey wishbone.  We’ll just have to see how long it takes.

 

Bottom line: even though it takes a little more time to correct a flawed woody root system, it’s well worth the effort.

An unusual company

This week I’m in Charlotte, NC as a guest of Bartlett Tree Experts.  In addition to providing tree services, this company also maintains the Bartlett Tree Research Laboratories and Arboretum. The latter includes over 300 acres of tree collections and ongoing research trials.  Here’s a sampling of the tree research we had a chance to observe:


Demonstration espalier pruning…


…and pleaching


Comparison of root barrier materials.  This area was covered with a sidewalk for a number of years and then exposed to observe tree rooting patterns.  The purpose of the research was to find which barriers were most likely to prevent sidewalk lifting and cracking.


A control – no barrier, lots of roots!


Black plastic – lack of rigidity allows roots to grow over (and through) the plastic, then under the sidewalk.


18″ rigid root barrier.  One of the more effective means of keeping roots out.


Removing circling roots before planting


A tree whose roots had been corrected before planting.  I think this had been planted in 2007, then lifted a few weeks ago.


A tree without root correction.  It didn’t grow any better than the corrected tree, and those circling roots are well on their way to becoming girdling roots.

This company employs a number of PhDs whose research is routinely published in arboricultural and horticultural journals.  It was fun to finally meet these researchers whose work I’ve been following for years.

Wouldn’t it be great if more companies put this much effort towards research?

WOW again (Why oh Why?)

I’m going along with the “dead tree” theme of the week, but doing a little prognosticating at the same time.  Bert and Holly showed you tree demise on site; I’m going to show you tree demise in the making.  We can call this “dead plant walking.”

I’ve done a few WOW postings in the past, often with a focus at what you might find at a nursery or big box store.  Here’s a recent find at an unnamed BBS, in the “topiary” section:

Unless you intend to have a giant stake as part of your topiary statement, this tree (actually a juniper) will morph into a prostrate form before your very eyes. Fortunately, it probably won’t live long once transplanted since it’s so overdue for potting up that the pot has split:

You can just imagine the nest of woody roots fusing into a functionless mass, can’t you?

Run, don’t walk, away from nursery plants like this.  You’ll be glad you did.

Does colored glass help root cuttings?

I get a lot of questions about a lot of different products and practices.  New topics send me to the scientific data bases and that’s where I went for today’s posting.  One of my garden writing colleagues asked me about colored glass rooters – glass containers in different colors that can be filled with water and a plant cutting.  The conventional internet wisdom, according to my colleague, is that green and blue glass rooters are the best.

The first mention I could find of such a practice is from an 1801 publication called The Cottage Gardener.  In it, we’re informed that for rooting cuttings “such coloured glass is useless; it has no influence over the production of roots.” Nevertheless, 200 years later web postings like “I have found that cuttings placed in colored blue or green glass root faster than clear glass” are taken as solid evidence that blue or green glass containers are best for rooting cuttings.

There is science behind different colors of light and rooting, but it’s a little more complicated.  Chlorophyll absorbs red and blue light best, so plants whose leaves are exposed to red and blue light grow well and tend to produce a healthy flush of roots.  On the other hand, plants whose roots are exposed to blue light have decreased root growth compared to those under white light conditions.  In this case, the photoreceptor called cryptochrome might be responsible for inhibition, as it is a blue light absorber.  Similarly, plant roots exposed to green light do not grow as well as those exposed to white light.

In my opinion, this is another example of aesthetics trumping science.  Of course colored glass rooters are more attractive that plain old glass jars.  And that’s a perfectly valid reason to use them as part of one’s home decor.  But it’s not science, nor is it necessarily the best way to encourage rooting.

What seems to be most important in rooting cuttings in water is to use indirect lighting (north-facing windows in the northern hemisphere, for example) so that the water doesn’t get too hot.  And keep in mind that not all species root well from cuttings.

Getting to the root of the problem

After getting off to a cool and soggy start, summer has come with a vengeance to Michigan, with heat indices expected to push 100 degrees by Wednesday.  Along with warmer temperatures, summer also means our research season is getting into full swing as well.  One of our biggest efforts these days involves our project to look at pre-plant storage and handling on shade tree liners.

 

As many GP blog readers are aware, emerald ash borer (EAB) has dominated the conversation regarding shade trees in the Midwest for the past 6-8 years.  Ashes made up 20 to 30% of the shade tree cover in many urban and community forests, so their loss has been devastating.  A major thrust of our extension programming during this time is to promote a wide range of ash alternative to increase species diversity.  One of the challenges we find in making this pitch is that many of the species we recommend (oaks, hackberry, baldcypress) are trees that nurseries often find difficult to grow from standard bare-root liners.

 

My graduate student, Dana Ellison, is in the second year of a project to look at some of the practices that growers use on the difficult to transplant species and some of the underlying causes of poor transplanting.  Dana is looking at a variety of attributes including plant water relations and carbohydrate status, but the order of business these days is roots.  Specifically we’re evaluating root growth potential of oak, baldcypress, and hackberry.  We’ve also included white ash, which transplant easily, as a positive control.

Graduate research assistants Dana Ellison (right) and Brent Crain (left) and undergraduate assistant Arriana Wilcox (center) pot up shade trees for root growth potential testing.

Root growth potential (RGP) is a common parameter in evaluating quality of reforestation seedlings but is measured less often on larger liner material.  The logic is pretty straightforward; a plant’s ability to initiate root growth after plating and re-establish root-soil contact is one of the biggest determinants of its ability to survive and grow.  A variety of systems have been used to evaluate RGP for seedlings – most involve growing seedlings for a set time (3 weeks is standard) in an aeroponic system and then counting or measuring new root growth.

Growing the trees in pea gravel makes it easy to get a look at new roots.

For Dana’s shade tree liners (5’-6’ whips) we’ve adapted a system based on the Missouri gravel bed system (which I first got to see in person at Jeff’s research nursery in Minnesota – thanks Jeff!).  Dana and her helpers pot the trees up in pea gravel in 25-gallon containers.  The trees are grown on for three weeks in a greenhouse while the roots are kept moist with spray stakes operated by a mist system timer.  After three weeks, we dump out the gravel, wash the root systems, and carefully count the number of new, white root tips.

Dana washing roots.

So what have we learned?  Well, the work is still on-going but some trends have emerged.  Baldcypress may experience some transplant issues but they don’t appear to be related to producing roots.  We had several baldcypress trees that produced 400 or more new roots during the RGP test – and, yes, we counted them all!  Red oak and northern pin oak, on the other hand, are very slow to put out new roots.  For hackberry trees, our other measurements suggest their transplanting issues may be related to their inability to re-hydrate after lifting, storage and transport.  These insights should help us provide some guidelines to growers to help them produce a wide pallet of trees for the landscape market and increase species diversity in the wake of EAB.

Counting roots.  Almost as much fun as it sounds…


The defending champion baldcypress: 614 new roots.

Update on root-rotted Cornus kousa

A little more than a year ago I posted a Friday quiz based on a failing Cornus kousa.The answer explained that our landscape has, in part, a perched water table that effectively rotted most of the roots of this poor tree over several years.  Last spring we moved it to a different section of our landscape where we know the drainage is better, and I’ve been monitoring its recovery since that time.


Cornus kousa leaves in 2007


Cornus kousa leaves in 2011

We were gratified to see that the leaves this year are significantly larger than those of previous years.  This tells us that root function has resumed, providing enough turgor pressure to expand the leaves to normal size.  It was especially helpful that we had one of the rainiest springs on record.

Take home lesson:  if a tree or shrub is failing in its current location, it’s worth digging up to see what’s going on.  Bad soil conditions?  Move it to a better location.  Bad roots?  Time to hone your root pruning skills.  But wait until fall to do this.  Transplanting this time of year is the most difficult for plants because of the increased water demands of warmer temperatures and expanding leaves.

Harvesting an Experiment

This has been an exciting week for me.  On Monday we started cleaning off 72 rootballs of various tree species that had been planted 5 years ago for a study.  These trees had been planted in containers and become potbound at the nursery from which we received them.  We treated them in one of three ways.  Either we did nothing (in other words we just dropped the pot bound tree in a hole), we used the standard methods that Universities recommend for slicing potbound roots (Four deep slits down the sides and a deeply cut X across the bottom), or we cut off all of the circling roots by cutting the pot bound root system into a box shape.

A root ball cut into a box shape

The plan was to harvest after 4 years to see what happened – we decided to wait 5 – and boy did we see some interesting stuff.  At this point our results are preliminary – we need to run statistics before we can say anything conclusively – but this is what my eyes tell me.

  1. Trees that had their roots cut into boxes suffered reduced growth the first few years, BUT, their root systems look as good as any root systems that I’ve seen – almost no circling.
  2. We planted our trees with the surface of the soil at the same level as the surface of the media in the containers – which is too deep in most cases.  For trees with circling roots this created a severe problem as the circling roots often surrounded the stem – potentially causing suffocation of the tree later in life.
  3. Root systems that were cut using the 4 slit method didn’t look much different from those that weren’t cut at all.
  4. The number of large roots emanating from all of the treatments appeared to be about the same (we’ll need to run the stats before I commit to this one).  This is particularly interesting because many people expect large roots that are circling to continue circling — but that isn’t what usually happens (unless the hole where the tree is planted has hard sides which can force the roots to circle just like the container did).


This root system was from a control — no root pruning at all, but still plenty of large roots.

No matter what the results/statistics end up saying there will be more questions.  For example, all else being equal, how damaging are circling roots to the health of a tree if the tree is planted properly (no stem tissue under the surface of the soil) and the circling roots are under the surface of the soil?  If the answer is that circling roots under the surface of the soil aren’t very damaging (after all, there’s no stem tissue for them to crush) then why are we bothering to try to root-prune pot bound plants at all – what we should really be concentrating on is planting at the proper depth.

All the above is hypothetical though – I just enjoy thinking about this stuff as the data starts to roll in.  As we get more definitive answers and start to run the statistics I’ll let you know more.

When trees attack!

We typically think of trees as the ‘good guys’; they shade our homes and yards, they take up carbon dioxide and pollutants from the air, they give us oxygen.  What’s not to like?  Well, like a lot of good guys, trees can also have a dark side.  One of the more sinister habits some trees have is getting into sewer lines.  Some studies estimate that trees are responsible for up to half of sewer line repair costs.  The prospect of trees getting into residential sewer lines is troublesome, of course, because it’s an invisible problem; we usually don’t know there’s an issue until there’s an issue.  Once tree roots get into sewers, they are often expensive and messy to deal with.  And I don’t mean just messy in the sense of having to call in a backhoe to dig up your yard.  Deciding who is responsible for the cost of cleaning up after a tree figures out its hit the mother lode can be a mess as well.  What if your neighbor’s sycamore finds its way into your pipes?  Or what if the culprit is the silver maple that you didn’t want but the city planted in the tree lawn anyway?  In some cases there are city ordinances that cover these situations.  For example, some cities will cover damage from city-owned trees provided they determine the city-owned tree caused the damage and the damage wasn’t due to a pre-exiting problem with the pipes.  Therein lies the rub.  As long as sewer pipes are intact and functional, tree roots have a hard time penetrating.  The problems usually arise when pipes crack or joints fail.  Once roots find an opening, it’s Katie bar the door.  This is why tree-sewer problems are most common in older systems with clay or concrete pipes that can crack over time.  Of course, the type of tree and location play a role as well.  Other factors being equal, fast-growing bottomland species are the most frequent offenders.  Danish researchers found that willow, birch, and poplar trees were responsible the largest number of root intrusions into sewer lines.  In many parts of the US, sycamore, sweetgum, and tulip-poplar can be added to the list.

Tree roots and sewer lines: a bad combination
So what’s a homeowner to do to get some sleep and not worry about tree roots planning a silent assault on the drain-lines?  Keeping fast-growing trees away from lines is a start.  But tree roots can grow a long ways and are pretty relentless; if there is a crack or a weak spot in the pipes, they will find it.  Keeping the system maintained and preventing entry is the key.  If the system has cracks, “Root-stopper” or “root-killer” products are available.  These are copper-based materials similar to ‘spin-out’ used on tree containers to prevent circling roots.  These will kill feeder roots that have entered into pipes, but roots are persistent and they’ll be back.  Plumbers have special tools that they can snake through the system that can cut through roots and clear blocked lines – at least for awhile.  If you have old sewer lines and have fast-growing trees around, you may want to consider hiring a plumber do a video inspection of your lines periodically (think of it as a colonscopy for your house).  If there’s a problem the plumber will be able to pin-point where it’s at and (hopefully) fix it before it becomes a major expense.

Trees can be good plumbers

A short follow up to last weeks post on girdling roots.  Just to reiterate, the point of the post was that we need to be careful not to jump to conclusions when assessing tree problems.  It’s important to look beyond the first defect we see and consider additional causes.  And to also reiterate, girdling roots can be a serious problem and can lead to tree failures.  The photo below shows an example of tree that was both planted too deep and had stem girdling roots.  The result was a weakened area in the trunk, which was subject to breakage during a windstorm.

Many people also assume that girdling roots restrict flow of water and nutrients in the xylem.  They can, but trees also have the ability graft roots and re-establish connections between roots.  In the study I mentioned last week, Phillip Kurzeja and his co-workers  traced water flow in ’manifold roots’ (a series of interconnected, girdled roots) by injecting dye.  The trees were subsequently felled and de-barked, allowing the researchers to determine whether the roots were still functional.  As shown below the girdled roots were able to re-establish their vasculature and continue to translocate water up the stem. So trees can be efficient at fixing their own pipes!

Image: Phillip Kurzeja

It is important to note that this phenomenon occurs between roots but not between roots and the main trunk – hence the concern for impact of stem-girdling roots, especially for trees planted too deep.