Tree research continued

Not to be outdone by Bert’s recent postings, I thought I’d show you what’s going on with MY tree research in Washington State.

As you might remember, we installed 40 1-gallon mugo pines and 40 B&B Japanese maples at the end of December 2011.  Here’s a photo of the site in April of this year:

I’ve been collecting data on above-ground growth during this year, but have had an unexpected twist to my research, as shown here:

That’s a pine tree.

Yes, we have moles…BIG moles apparently…in Puyallup.  There’s not much I can do besides move the soil away, but obviously the pine trees are not going to be happy with this additional treatment.  The maples are tall enough where it’s not going to be much of an issue.

Note to self: next time install guard Dachshunds next to pine trees. (Thanks to the Fremont Tribune for this great photo!)

A guest blogger (sort of)

One of the best things about my job is I get to work around bright, enthusiastic young people everyday.  And not just students here at MSU.  Through conferences, meetings and other contacts I get to interact with students at other universities as well.  Over the last couple of years I have had a chance to sit in on a couple talks by Alison Stoven O’Connor, who is an Extension Agent and Ph.D. student under the direction of Jim Klett and Tony Koski in Horticulture and Landscape Archetiecture at Colorado State University (and you thought you were busy!).  For her Ph.D. research Alison is working on a subject near and dear to the hearts of the Garden Professors; nursery production and tree root development.  After I saw her talk at the ASHS meeting this summer I invited Alison to take slot as a guest blogger but she declined, citing her time constraints – we’ll call it an excused absence.  She did, however, graciously share some photos from her trial which, as you’ll see, pretty much speak for themselves.


A brief run-down on Alison’s study.  She grew Chanticleer pear trees in #15 containers, including both standard black plastic containers and Smart Pot fabric containers in summer 2010.  After growing the trees in the nursery for the summer, she transplanted the trees into a landscape-type planting in the fall of 2010.  Last week (remember you come to the Garden Professors to get the latest!) she began sampling the roots of a subset of her trees with the aid of a local landscape company with an air spade.  The depth of rooting appears to be consistent regardless of the type of container the tree was grown in.  Width of the root system; that’s another story… While Alison has a ways to go in gathering and analyzing data, the photographic evidence looks pretty good for the Smart pots over the status quo.


Trees in nursery production.



Trees in the ‘Landscape’ after transplanting,



Air spading to harvest roots

Root systems two years after planting in the landscape.  Left – tree grown in conventional black plastic pot.  Right – tree grown in Smart Pot.  630 miles between East Lansing and Minneapolis and I can already hear Jeff gloating, “Neener, neener, neener…”

Fruits and Plains

Recently there have been a number of plant related books that have done really well in terms of sales.  Brother Gardeners is one and What A Plant Knows is another.  Personally, I think both of these books are nice additions to any horticulturists bookshelf.  But there are always those books that have been forgotten.  One of those books is Fruits and Plains: The Horticultural Transformation of America by Philip J. Pauly.  Published in 2008 this is an accurate history (much more accurate that anything by Pollan for example — Not that Pollan writes bad stuff, but let’s face it, he’s a storyteller) of the evolution of horticulture in the United States over the past few hundred years — If you really want to know the history of horticulture here in the US then this is probably the best place to start.  I can’t recommend it enough.

SoMeDedTrees update

Things have settled down briefly here and I have had a chance to summarize some of the data from the container tree transplanting experiment we installed earlier this year.  For those that aren’t familiar we installed two tests this summer using 96 ‘Bloodgood’ plane trees grown in 25 gallon containers that were leftover when we completed an earlier trial in our Pot-in-Pot nursery.  I decided to use this as an opportunity to look at some tree transplanting recommendations.   With input of our GP blog readers, we installed two tests.  In both tests we applied three treatments to the tree root-balls before planting (‘shaving’ the outer roots to eliminate girdling roots; ‘teasing’ apart the rootball to eliminate girdling roots, and a control or ‘pop and drop’ to use Linda’s nomenclature).  At one site we fertilized half the trees at planting and left the others unfertilized.  At the second site we mulched half the trees with 3” of ground pine bark and left the others unmulched.


On the fertilizer trial we have not seen anything remarkable.  We conducted measurements of leaf chlorophyll content using a SPAD meter (a device that measures light transmittance through leaves) but did not see an effect of either fertilizer or root ball treatments.  This is not completely surprising.  In the nursery trial we fertilized the trees at standard production levels, so their nutrient status was pretty good at the outset.  What will be interesting is to see if either treatment at planting has a longer term impact.


In the mulch study we have seen some more immediate impacts.  We measured soil moisture to 15 cm (6”) and 45 cm (18”) inside the rootball and just outside the rootball periodically during the summer.  Soil moisture levels were consistently higher for the mulched trees that for the trees that were not mulched (Fig. 1), especially at the shallow (15 cm) depth.

Figure 1. Soil moisture of trees with and without mulch in the SoMeDedTrees study, summer 2012. (Sigmaplot wizardry by Dana Ellison)

This was reflected in tree moisture stress levels during August.  We measured predawn water potential with a pressure chamber.  Using a pressure chamber enables us to estimate the level of tension with which water is being held inside a tree.  We remove a leaf from the tree and put it in a chamber with the cut end sticking out.  We gradually increase the pressure in the chamber until we see water appear on the cut end.  The more stress the tree is under the more pressure we have to apply to get water back out. In this case, mulching, by virtue of the fact it increased soil moisture, resulted in lower water potential values, indicating less stress (fig. 2).  The root ball manipulation treatments, on the other hand, did not affect tree stress.


Figure 2. Mean pre-dawn water potential (in -MPa) of plane trees in the SoMeDedTrees study, August 2012.

So where does that leave us?  Well, as we’ve noted all along, this is long-term trial.  The plan is to track the trees over 3-5 years and maybe longer.  But long-term responses are the cumulative results of series of shorter-term effects.  So far, mulching appears to be the only factor that has made a difference but we are still early in the game.

Ecosystem services: Am I going to get a bill?

Spent last Friday in a departmental faculty retreat – you know, the “vision thing”  – S.W.O.T. analysis, where are we going to be in five years, etc.  But we actually got some things accomplished. One of the more interesting aspects was discussing trends in horticulture, both popular and practical, and how we could respond. One of the reoccurring themes throughout the day, especially related to urban agricultural/horticulture, was ecosystems services. I’ve heard the term mostly from environmental science and urban forestry folks.  But also seems fairly appropriate for us horticulturists, who are constantly trying to explain what, exactly, we do.

The definition offered by the American Institute of Biological Sciences (“Bringing biology to informed decision making”) is pretty good:

Ecosystem Services are the processes by which the
environment produces resources that we often take for granted such as
clean water, timber, and habitat for fisheries, and pollination of
native and agricultural plants. Whether we find ourselves in the city or
a rural area, the ecosystems in which humans live provide goods and
services that are very familiar to us. [They include:]

  • moderate weather extremes and their impacts
  • disperse seeds
  • mitigate drought and floods
  • protect people from the sun’s harmful ultraviolet rays
  • cycle and move nutrients
  • protect stream and river channels and coastal shores from erosion
  • detoxify and decompose wastes
  • control agricultural pests
  • maintain biodiversity
  • generate and preserve soils and renew their fertility
  • contribute to climate stability
  • purify the air and water
  • regulate disease carrying organisms
  • pollinate crops and natural vegetation”

Horticulture, as a discipline, touches on so many of these areas.

My question to our readers: does the term ecosystem services mean much to you? Or do you consider it jargon, best kept to grant proposals and impact reports?

Another WOW (why oh why) – “biodegradable” mesh for plugs

David Hobson, a garden columnist, sent me this great photo of his petunia planted earlier this year. Take a look at the root growth (or lack thereof):

I’m not sure where this particular product came from, but it looks a lot like a FERTISS propagation plug.  Here’s a description from their website of this product.”FERTISS is a ready-to-use, pre-filled propagation tray system. Cuttings are placed in a mixture of peat and perlite wrapped in a non-woven fabric. Roots of young plants will easily penetrate this fabric and enter the airspace between the fabric and the plastic cell wall. Roots are naturally air-pruned, resulting in a faster and better take, increased lateral branching, and improved transplanting performance.”

It sure doesn’t look like roots “easily penetrate” this fabric, at least when gardeners get them potted up at home.  And though I can’t see the top of the plant, I’m guessing it didn’t show “improved transplanting performance,” especially compared to a plug from a traditional liner pot.

Nowhere did I find what this “non-woven fabric” was made of (though there are allusions online to it being biodegradable), but it’s just one more impediment for plants – and gardeners – to deal with.

New study on pesticide use and GMOs

Some environmental extremists discount agricultural research done by universities, because they receive funding from Big Ag and therefore their researchers can’t be trusted. So this news report of a recent study by one of my Washington State University colleagues is doubly important: it dispells this baseless assertion and it provides some significant – and troubling – information about pesticide use and GMO crops.

Briefly, the article links an increased use of herbicides as a result of increased use of GMOs such as Roundup-ready crops. Weeds build up resistance to herbicides over time, meaning that Roundup becomes less useful as a weed killer and farmers have to turn to more toxic substitutes like 2,4-D to control weeds.

Dr. Benbrooks’s results, published in a peer-reviewed journal, are contested by the chemical industry, and other scientists question the seriousness of the problem. But next time you hear someone malign university scientists as being in Monsanto’s back pocket, please refer them to this post.