Tag: woody

The roots of the rhody problem

There were several good shots at analyzing Friday’s unhappy rhododendron.  Mature leaf size can be determined by light levels, as both Lisa B and Tom &  Paul suggested.  Moving a plant from a low to high light environment could cause this change in leaf size.  This rhododendron hasn’t been recently transplanted, however, so we can eliminate light levels as a cause.  (And there was no other impediment to light, such as the presence of shading plants.)

Lack of nitrogen was mentioned as well; but a lack of nitrogen would have resulted in chlorosis in newer leaves as well as smaller leaf size.  In this case, the new leaves are not chlorotic.  (The chlorosis on the older leaves is probably a phosphate-induced iron or manganese deficiency.)

Foy alluded to issues with water…and indeed that’s what I believe is happening with this rhododendron.  Plants that exhibit smaller mature leaves in subsequent years are often limited by water.  Full turgor is needed to force leaves to expand fully; without this physical pressure from inside, leaves fail to expand and once cell walls have lignified, leaf expanion ceases. 

Lack of sufficient water during leaf expansion could be related to irrigation, though in our wet spring climate this is rarely a factor.  More likely is a problem with the roots themselves.  Definitive diagnosis would require digging up the plant to find out whether its roots are still encased in clay and burlap (my guess) or if something else is restricting their ability to grow beyond the planting hole. 

Friday puzzle: unhappy rhododendron

Today we have a diagnosis question. Consider this unhappy rhododendron:

While there is more than one problem with this poor thing, the one I’d like you to think about is why the newer leaves are smaller than the old leaves. (They are fully mature.) There are two parts to this question:

1) What is the physiological reason that the leaves are smaller? (In other words, what is directly causing this difference?)
2) Knowing this, what does this tell you about the underlying problem? (This is related to diagnosing what’s happening in the landscape that you could actually see if you knew where to look.)

I hope that’s not too confusing! I’ll monitor the blog over the weekend and add clarification if I need to.

Answer on Monday!

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.

Tree terrors continue

You might remember back in October 2009 I gave one of the first Friday quizzes.  The featured tree had epicormic shoots, and Monday’s answer revealed the neglected wire staking that was slowly girdling the main trunk.  (Be sure you click on those links to see what the tree looked liked in 2009.)

I thought you might be interested to see what this tree looks like now:

A picture is worth a thousand words….many of those unprintable.

Update January 2022 – in response to a reader question, here is the tree in 2019 thanks to Google maps.

Unspeakeable Acts of Pruning

(Hey, I think it’s Tree Week on the GP!)

Our land has a nice buffer of big, old oaks, hickories, and maples between us and the two-lane highway.  Power and phone lines thread through the middle of them. Thus, I have nightmares about orange Asplundh trucks.

So with much concern, I noted that utility crews and
subcontractors have been out in full force in our rural area,
inexplicably leaving one tree and then “pruning” another.

OMG that's awful

I pulled over and snapped this latest atrocity last night. The power lines are to the right (not in photo). As this is only a mere mile or two from our property, I may sit at home on the porch next week with the shotgun in my lap.

Tree teaser untwisted

Once again you had some great diagnoses!  The popular view was neglected staking material, and you were right:

Peter’s answer was my favorite (I love puns – the worse the better!).  Tom, I hestitate to ask about your previous experience here….

As usual, thanks to all of you for playing our quiz.  I’ll try to be better about doing this every Friday.  Our survey results indicated you like this feature a lot.

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.

Girdling roots: The source of all evil in the world?

One of the most widely discussed topics in arboriculture and tree care these days is the problem of girdling roots.  Virtually every conference or workshop on tree care has a speaker or speakers on how poor planting technique or poor nursery practices lead to girdling roots and their subsequent correlation with poor tree performance, tree failures, global warming, the soaring Federal budget deficit, and the batting average of the Seattle Mariners.  Before we go any further let me state categorically that I do not think girdling roots are a good thing; nor do I think any of the consequences mentioned are a laughing matter – especially the Mariners’ batting average.  I do think, however, that we often see a rush to judgment as soon as girdling roots are found on trees that are declining or have died.  I attribute at least part of this to the increased availability of air spades for excavating tree roots.  I have nothing against air spades; they are useful tools and a great way to non-destructively examine and treat roots and even move trees.  The problem is that often when people see a tree in decline they examine the roots, see a girdling root, conclude that was the problem and blame the person that planted the tree (unless they were the person that planted the tree, then they blame the nursery).

 

Example of oak tree with leaf scorch (Photo Phillip Kurzeja)

A recent study here at Michigan State presented by Phillip Kurzeja at the recent Arboriculture Society of Michigan ArborCon, points out the importance of looking beyond girdling roots in assessing tree problems.

The problem:  Oak trees at several locations on the MSU campus have been suffering severe leaf scorch.  In some cases virtually 100% of the leaves on the trees are affected and growth has been severely affected.  Examination of the trees by a pathologist ruled out bacterial leaf scorch, suggesting that the problem may be abiotic.  The researchers looked at a battery of variables including degree of leaf scorch, number of girdling roots, planting depth, soil compaction, foliar nutrition, leaf water potential, and leaf photosynthetic function.  Most importantly, they looked at these traits on trees without scorch as well as trees with scorch.

Evaluating girdling roots (Photo Phillip Kurzeja)

The results:  Trees with mild or severe scorch leaf scorch had girdling roots.  At this point one might have leapt to the conclusion that the girdling roots were responsible for the leaf scorch.  But girdling roots were also found in trees that did not have any leaf scorch.  In fact, in some cases the healthy trees had more severe girdling roots than trees with the worst leaf scorch.  So, what factors differed between trees with scorched and un-scorched leaves?  The researchers are still working on the analyses but the most obvious differences were that trees with leaf scorch were consistently planted deeper and had lower levels of foliar manganese than healthy trees.

 

The presentation I saw did not include data on soil pH or soil nutrient levels, so it’s impossible at this point to establish causal relationships among planting depth, foliar manganese, and leaf scorch.  But, for those who have to answer the ‘what’s wrong my tree?’questions, this study does point out the importance of keeping an open mind and looking at a variety of factors and not leaping on the first defect to appear.

Planting trouble: multiple trees in one hole

[I enjoyed Jeff’s Valentine story so much that I thought I’d stick to the theme of togetherness…for better or worse.]

A week or so ago a reader asked about the practice of planting three or four fruit trees in the same hole.  Having not heard of this before, I checked on the web and found many “how to” pages geared to home gardeners who either want a longer harvest of a particular fruit (early to late) or a mixture of different species.  Doesn’t it sound just great, especially for smaller urban yards?

One of these sites has these written instructions: “Plant each grouping of 3 or 4 trees in one hole at least 12 to 15 inches apart.”

Now, I’m sorry, but this is just asking for trouble down the road.  Readers of this blog know that root systems extend far past the drip line, and that roots from different trees are going to compete with one another.  You’ll end up with three unhappy trees, all jostling for space and resources, just like kids in the back seat during those long car rides.

But wait! you might say.  There’s research on high density tree planting, and it’s been shown to increase fruit yield on a per acre basis!

Yes, in fact there is a lot of planting density research on many different species of fruit trees.  What’s considered by researchers to be “high density” varies, but it rarely exceeds 2698 trees/acre (6666/ha for our international readers).  Optimal and sustainable levels of high density planting are also variable, as they depend on not only species but rootstock and the crown architecture; 1214/acre (3000/ha) might be a mid-range number.  This can be converted to a per-tree requirement of 36 sq. ft. or a 6’x6’ planting area.

How does this compare to the 12-15” recommendation given earlier?  If we’re generous and use the 15” recommendation, this translates to 6.25 sq. ft. per tree or 6970 trees/acre.  The 12” recommendation would lead to a whopping equivalent of 10,890 trees/acre.  (And no, it doesn’t matter if you’re using dwarfing rootstock or not; most of the higher densities in the literature are for dwarfing rootstocks.)

You don’t have to be a math whiz to see that these densities are totally out of line with reality.  Sure, you can probably keep overcrowded trees alive with lots of water and fertilizer, but they’ll be under enough chronic stress so that pests and disease might take hold, and fruit production will likely be poor.  And it’s about as far from a sustainable practice as you can get.