Author: Bert Cregg

Questions on sustainability

Linda’s recent post on the sustainability of topiaries got me to thinking, is any horticultural practice sustainable?  And, does it matter?

 

Picking up on the topiary theme I thought of the ultimate form of tree manipulation, bonsai.  I few years ago I visited the National Arboretum in Washington DC, which includes an incredible bonsai display.  Some of the bonsai specimens in the collection originated in Japan and are over 300 years old.  Is 300 years long enough to consider this a sustainable practice?  Does it matter as long as there are individuals willing to devote the time and effort to tend and prune these awesome and inspiring plants?

 

More recently I visited the International Rose Garden at Washington Park in Portland.  Established over 90 years ago the garden is one of the premier attractions in Washington Park and in Portland.  Maintaining the garden, however, requires paid staff and an army of volunteers.  Is 90 years long enough to consider this sustainable?  Does it matter as long as the city is willing to commit resources and volunteers are willing to line up to dead-head and pull weeds?

 


Closer to home, I maintain about an acre of my place in lawn and various beds – trees, shrubs, herbaceous perennials and even a few (gasp) annuals.  Is this sustainable?  Does it matter as along as my family and I enjoy our surroundings and are willing to commit the time and effort to mow, weed, edge, prune and dead-head?

What’s old is new again

While the Emerald Ash Borer (EAB) continues to expand in the upper Midwest (see http://www.emeraldashborer.info/files/MultiState_EABpos.pdf  for a current infestation map), EAB is old news here in Michigan, especially in the southeastern part of the state.  Efforts to restore urban and community forest canopy lost to EAB will continue, however, for the foreseeable future. In 2003 we established an Ash Alternative Arboretum MSU Tollgate Education Center in Novi, MI – which is near ‘Ground Zero’ for the EAB infestation in North America.

 

The planting offers some insights into selecting alternative landscape trees to replace ashes.  A couple of elm cultivars, in particular, have emerged as shining stars in the demonstration planting that includes five specimens of 37 different species and varieties.  All trees were planted as 1½”-2” bareroot liners by Tollgate volunteers.  Tollgate farm manager Roy Prentice has overseen the maintenance of the planting.

 


Accolade elm (Ulmus japonica × wilsoniana ‘Morton’)  Compared to most of the other selections planted in the arboretum at Tollgate, Accolade elm looks like a man among boys.  Growth of these trees has been outstanding – the trunks of the trees have grown fast enough that they have split off their plastic rabbit guards (see photo).  Like Triumph elm, Accolade elm has dark green glossy leaves and develops into a large tree.  Although elms are often thought of ‘ugly ducklings’, both Triumph and Accolade are quickly developing well-formed vase-like crowns.

 


Triumph elm (Ulmus ‘Morton Glossy’) has also done very well at the Tollgate planting.  This elm develops a vase-like crown with age and has dark green, glossy leaves.  A large tree to 55’.

 

The elms are part of series of elm cultivars that have been developed with high tolerance of Dutch elm disease.  Most of the new elms are hybrid crosses with Asian and European elm species, though selections of American elm that are tolerant of Dutch elm disease are also available in the nursery trade.  The irony in all of this, of course, is that native American elms were devastated by another introduced exotic pest, Dutch elm disease.  As elm trees were rapidly lost during the 1950’s, 60’s, and 70’s, ash trees became a popular replacement due to their ease of transplanting, growth rate, broad site tolerance and pest resistance (yet another irony).  Now we’re promoting elms to replace ashes.

 


Street scene before and after Dutch Elm Disease.  Photo: theprincetonelm.com

The moral of the Dutch Elm Disease and Emerald Ash Borer stories is that it’s critical to avoid over-reliance on one species or even one genus – even a native one.  In Michigan some of our urban and community forests are over 50% maple.  As global trade increases and the potential for destructive pests to hitch-hike around the world rises, the best hedge against catastrophic tree loss is to plant a broad and diverse array of adapted trees.

Plastic grass and organic gardens

One of the best cures for writers’ block for a Garden Professors is to spend a little time in front of the tube watching home gardening shows.  Now, to be sure, there are useful nuggets of information that can be gleamed from an hour or so of gardening or landscaping on HGTV or PBS Create.  But there are moments when I just stare at the TV in disbelief and go, ‘Have these people lost their frickin’ minds?’

 

A recent case in point, a half-hour gardening show devoted to installing an ‘allergy free’ backyard for a youngster, we’ll call him Billy, with environmental allergies.  Let me state up front I am in no way minimizing the seriousness of environmental and related allergies.  I suffer wicked seasonal allergies (yes, I know, poor career choice) and I have several close friends whose children have severe allergies.  I realize allergies can seriously affect quality of life and, in the cases of some food and insect allergies, can be a matter of life or death.  And I realize that a parent will do just about anything to keep their kid healthy.  Nevertheless, some of the practices promoted on this show strained all manner of credibility.

 

First, since Billy is allergic to grass, the landscaper replaced all of the grass in the backyard with synthetic turf.  Grass allergies are among the most common allergies but what is it about grass that most people are allergic to?  Pollen.  According the National Institutes of Health just keeping grass mowed is a simple preventative measure to reduce grass pollen.  Synthetic grass may have issues of its own with molds and there are remaining uncertainties regarding the safety of the used-tire derived crumb rubber used in some fake turf.   And if Billy has issues with pollen, I saw a much bigger problem looming like an 800 lb gorilla as the camera panned back from the picture-perfect synthetic lawn: Trees, specifically dozens of oaks and pines in the woodlots beyond the backyard.  I joined the show part way through but the overall landscape looked like the Southeast, perhaps Georgia or the Carolinas.  Even if the fake turf does reduce grass pollen in the back yard, Billy will scarcely notice as a yellow-green cloud of tree pollen envelops his house every spring.

 

Next, in addition to wanting a place to play, Billy wanted a vegetable garden.  Actually, given Billy’s obvious disinterest during this part of the show I don’t think he was really that interested in vegetables but the producers knew they couldn’t fill a 30 minute show with just fake turf.  Assuming Billy really was into vegetables the solution, of course, was an organic garden.  Why an organic garden is a panacea for allergy sufferers was never explained in the show; apparently pollens and molds don’t hang out in organic gardens.  The choice of vegetables was curious as well.  Billy got to plant squash and watermelons; guess no one bothered to tell Billy that cucurbit allergies are among the most common food allergies for people predisposed to pollen allergies.  For good measure, Billy got to plant some corn – doubt that could ever produce any pollen…

 

Bottom-line: take the info from the garden shows with a grain of salt and consider the source of the information.  Often times these shows are limited to whatever local source they could dredge up.  Do you really want to rely on a landscape contractor to make decisions about your child’s allergies and health?  Enjoy the shows but keep your skepticism handy and be ready to do some fact checking on your own.

Riding the storm out

This past weekend marked our first real bout with severe thunderstorms here in Mid-Michigan.  Several lines of storms moved through the mid and southern part of the state and northern Ohio.  The storms in southern Michigan and Ohio also spawned some tornadoes.  Around here, storm damage was confined mainly to downed trees causing power outrages and some damage to homes and buildings.

Severe weather outbreaks provide some opportunities to observe tree failures and gain insights into how they can be prevented.  Or, as Yogi Berra put it, “You can observe a lot just by watching”. I was at a little disadvantage in scouting out tree damage from out most recent storm because we were traveling over the weekend and  I wasn’t able to get out and about to survey damage until Monday evening.  As it turns out the area most heavily affected by the storm is also fairly affluent.  Folks in these neighborhoods don’t tolerate downed trees lying around very long.  Nevertheless, I did make a couple of interesting finds.

 


A common sight after a storm in this area is wind-throw in shallow-rooted species, such as spruce and pines. We didn’t see a lot after the current storm, which was probably due to the fact that the storm moved through quickly – most of the high winds lasted only a few minutes – and the storm was not preceded by prolonged heavy rains.

I don’t have any specific data but I have seen several cases where wind-throw was occurred on trees in which mulch was underlain with landscape fabric.  Perhaps coincidence, but another strike against the stuff in my mind.

 


This maple provided one of the best (or worst) examples I have seen of planting too deep.  The tree snapped off about 6” below ground line.

Note that there are plenty of pretty stout roots that look like structural roots near the surface, but none of these originated near the current ground line.  The tree was on private property and time constraints prevented me from getting permission to do an excavation, nevertheless, it would be interesting to try to find the original root flare.

 


By far the most common problem in this storm, and most of our typical thunderstorms, was large limb breakage associated with narrow crotches.  This occurred in a variety of species; oaks, maples, elms, pines.  Narrow branch angles often form from multiple leaders, which results in weak branch attachment as included bark forms and gradually reduce the proportion of wood attaching the branch to the tree.  The encouraging thing, or maybe discouraging depending on your point of view, is that this is one of the most easily preventable tree defects.  Pruning double leaders or multiple leaders back to single leaders and eliminating other poor branch angles when small can easily prevent this type of breakage.  For most of our garden-variety thunderstorms, eliminating narrow crotches would probably eliminate 50% or more of our tree-related storm damage.

Good to the last drop

As part of our discussion of the relative merits of fall planting, Linda mentioned an article in Arboriculture and Urban Forestry that suggests that frequent, light irrigation might be better for landscape trees then the usual recommendation of infrequent soakings.  While I will withhold final judgment until I see the article (I did a scan of the last two year’s table of contents for A&UF but missed the article in question), here’s my rational for following the standard recommendation.

 

First, the context.  In discussing landscape tree irrigation I am talking about watering trees during establishment, typically during the first year after planting and maybe the second if the tree is lucky.  The goal of watering in this case is ensuring survival.  The questions are whether deep soakings are more likely to encourage deeper rooting where water availability is less variable than near the surface after irrigation ceases and whether infrequent watering increases drought tolerance over more frequent irrigation.

 

Roots follow resources
As my Woody Plant Phys students quickly learn, we avoid the teleological ‘roots seek out water’; nevertheless, roots do proliferate where resources are available.  A couple of illustrations.  As a Tree Physiology Project Leader with International Paper I supervised a 25 acre hardwood fertigation trial.   Trees were watered daily via drip irrigation system with emitters spaced every 3’ down a row.  As part of the study we did periodic root harvests.  My technicians quickly learned it was an easy job: just look for the drip emitters – every three feet there was a mop of roots right next to the drippers.  The notion of roots following resources is also widely reported in the ecology literature on tree utilization of ‘patchy resources’ (e.g. Gloser et al. 2008 Tree Phys 28:37-44 ).  Other factors being equal deeper watering should result in deeper rooting.

 

Trees habituate to frequent irrigation
Another short rotation forestry example.  In eastern Washington and Oregon forestry companies Potlatch and Boise Cascade operated intensively managed ‘fiber farms’ which grew 70’ tall, 7” diameter hybrid poplars on a 7 year rotation.  To maintain these growth rates, trees were irrigated daily.  But there was a downside: If one day’s irrigation was missed the leaders to the trees would start to wilt.  Three days without water would result in leaf drop. The daily irrigation was great for growth but it turned the trees into physiological wusses.

 

Periodic water stress improves drought tolerance and survival
A common adaptation for trees to tolerate drought is osmotic adjustment, which is an active accumulation of solutes that enables plant cells to maintain turgor pressure during dehydration.  Plants that have acclimated to stress via osmotic adjustments and other physiological adjustments are able to survive better during prolonged drought than plants that have not been pre-conditioned.  For example ponderosa pine seedlings that had been subjected to brief drought events survived a terminal dry-down two weeks longer than seedlings that had been watered 3 times a week before the final dry-down (Cregg 1994 Tree Phys. 14:883-898.

 

What would it take to change my mind?
Obviously some of my examples here are anecdotal (though there’s plenty of hard data on osmotic adjustment and other drought conditioning effects on trees).  To recommend frequent (2 or 3 times a week), shallow irrigation I would need to see: a well designed and executed experiment that compared frequent irrigation to periodic (once every 7-10 days) applying the same amount of water weekly (0.5 to 1” per week) for the first year and then documented improved survival of the trees after irrigation had been discontinued.  I’m not saying it’s not possible but it goes against my personal observations with irrigated trees in a variety of settings and relevant data with which I’m familiar.

Is Fall Really a Great Time to Plant Trees?

One of the joys of working on a university campus is that construction never seems to end.  As near as I can tell there are about 3,000 orange construction barrels that permanently reside on the MSU campus that simply get shuffled from one end of campus to the other every few months.  Along with all the construction comes a never ending series of new landscape projects.  Driving by one of the most recent projects the other day got me to thinking about the myth of Fall planting.  In numerous extension bulletins and certainly in nursery sales advertising we hear that “fall is the perfect time to plant trees”.


Photo: Dana Ellison

The recent fall planting job on our campus gave me pause to think about this.  I haven’t had a chance to completely survey the carnage but I suspect about a third of the trees will need to be replaced.  Obviously there are lots of things that may have gone wrong here, irrespective of when the trees were planted and one exception doesn’t prove the rule.  Nevertheless when I look back on the planting disasters I’ve been called in to inspect over the years a disproportional share (I’d say by a factor of two or three to one) are fall planting jobs.

 

What gives?  Well, the notion that fall is a great time for planting is built in a faulty premise, at least for this part of the country.  Probably the most commonly cited reason for fall planting is that trees grow a lot of roots in the fall.  This assumes that since there’s no shoot growth occurring, trees automatically shift reserves below-ground.   There is certainly a ‘pecking order’ of carbohydrate distribution within a tree based on relatively strengths of sources and sinks.  But there’s one factor that trumps all others: temperature.  Soil temperature is the biggest driver of root growth.  Measurements of new root growth in a cottonwood plantation in Wisconsin provide a classic example.  As temperatures decline in the fall, new root growth essentially ceases.  For trees that are well established, this is no problem.  For trees that have just been transplanted and need to re-establish root-soil contact this is a tough row to hoe.  Throw in a tough Michigan or Wisconsin winter and the tree’s facing an uphill climb.

 


New root growth of eastern cottonwood (top) and soil temperature (bottom). Source: Kern et al. 2004. Tree Phys. 24:651-660.

Again, most planting failures have multiple causal factors.  Even if the trees on this site had been planted in the spring, they may have still experienced problems.  My point is that a more accurate statement is “Fall is an OK time to plant trees”; not the ‘best’ time or even a ‘great’ time.  I think these statements are often driven by the fact the fall is a slow time for nurseries and landscapers.  When homeowners or landscapers ask me about fall planting the first thing I ask is if there is any reason why they can’t wait until spring, the real ‘best’ time for planting.

Every survivor has a story

It’s been suggested, not unfairly, that the Garden Professors are sometimes a little ‘Tree-Centric’.  As a forester and tree physiologist by training, I’m probably the guiltiest among my co-conspirators on that count.  But occasionally I do notice things less than 10’ tall and lacking a single, woody trunk.

 

When weather permits I like to take my lunch down to the MSU annual trial gardens behind my office here at the Plant and Soil Science Building.  Every summer the annual gardens are awash with the color of impatiens, geraniums, petunias, and other annuals.  This time of year, however, it’s bulbs that steal the show.  This spring there was a display of bright pink tulips that was especially striking.  Wandering by the beds recently I noticed a tag in one corner; ‘Susan Komen mix’.  For those that aren’t aware, Susan Komen lost a long, brave battle with breast cancer in 1980. The foundation founded by her sister, Susan G. Komen for the Cure, is the leading advocacy and fundraising group for breast cancer awareness and research in the US.  Komen for the Cure also provides services and advocates for our country’s two and half million breast cancer survivors.

In many ways, tulips are a fitting symbol for breast cancer survivors and the brilliant pink show made me think of a cancer survivor I know, my college girlfriend, Lisa.  I remember learning about her cancer nearly two years ago.  We had followed our own paths after our undergrad days and contact was sporadic as we each set out on careers and started families.  I missed her at our 30th high school reunion but found her number in the reunion directory and rang her up. The words hit like a punch in the stomach, “I underwent breast cancer surgery and treatment this past winter.”  I was stunned but in the next instant knew her trademark grace and humor were still intact.  “Yeah, when the reunion notice came out I had just lost both my boobs and all my hair.  Ya know, I just wasn’t up for all the ‘Hi, how are ya’s?’”  Today, Lisa remains cancer-free though after-effects of radiation treatments linger.  Through the wonder of Facebook we now keep up on each other’s awesome and talented kids.  She’s looking forward to two year’s cancer-free in July and then the all-important 5-year mark beyond that.


So, what does all this have to with landscape horticulture?   My friend and colleague Art Cameron concluded a talk at our Master Gardener College last Saturday with a quote: “To plant a garden is to believe in tomorrow.”  So much of what we in do horticulture is an expression of our faith in the future.  When we plant tulips in the fall we know they must endure dark, cold days each winter in order to bloom the next spring.  Breast cancer survivors and their families have to endure more than their share of darkness to see brighter days. We’ve become a society obsessed with instant gratification and the old cliché ‘stop and smell the roses’ seems trite and shopworn to a lot of folks.  But gardens connect us to the earth and to each other and provide the perfect place to take time and reflect on things that really matter.


According to the American Cancer Society nearly one in eight women in the US will develop invasive breast cancer in their lifetime.  To learn more, read breast cancer survivor stories, and to support breast cancer research go to www.komen.org

Everything is obvious once somebody shows you…

It’s amazing how many things in life seem complex when we try to figure them out for ourselves but then we end up smacking ourselves on the forehead when someone shows us how simple it really is.  The infield fly rule comes to mind.  Some colleagues of mine here at Michigan State may be on their way to such a solution for the problem of white grubs in lawns.  Drs. Dave Smitley (Entomology), Kurt Steinke, and Trey Rogers (Crop and Soil Science) are investigating the effect of mower height on turf damage from grubs.

European chafer grub.  Photo: David Smitley

The premise is simple: White grubs damage turf when they consume about 75% of the turf roots present.  Raising the mowing height of most standard mowers from 2” to the highest setting (usually 3 ½”) also results in more root growth; often by more than double.  Since there’s a limit to how much root mass grubs can consume, increasing the amount of roots ensures the damage threshold is never reached.  The working hypothesis has been confirmed by greenhouse tests and now the researchers are taking to the field.


Chafer grub damage.  Photo: David Smitley

This may turn out to be another example of how raising mower height and not trying to make your lawn look like a golf course fairway can reduce inputs and keep your turf healthier.

Spruce brown-out solved

Gall adelgids are certainly a problem in these parts, especially on blue spruce.  But the ‘problem’ in this case is not a pest.  This year, as in several recent years, spruces are developing copious amounts of pollen cones.  Once the pollen is shed, the cones dry up and turn brown.  Many homeowners mistake these for insect galls or sign of some other pest activity.
In many conifers, pollen cones occur on the lower portion of the crown while seed cones occur in the upper third as an evolutionary adaptation to reduce selfing.