Bert Cregg

Silence of the lamb chops

One of my ‘other duties as assigned’ this time of year involves serving as The Christmas tree Guy and responding to various media inquiries about Christmas trees. Last week I posted a link to a media story about Christmas trees on the Garden Professor Facebook page. That post drew a response from Kyle Fletcher Baker who derided cut Christmas trees as “murder of the innocent.” My initial reaction was, “Jeez, Kyle we’re talking about fir trees here not lamb chops or veal.” But Kyle’s post serves as a reminder that there are many people that object to cutting trees for Christmas decoration – no word on how these folks feel about cut flower arrangements but that’s another story. In some cases this objection stems from the belief that Christmas trees are cut from native stands of trees. In fact, virtually all Christmas trees sold at tree lots are grown on tree farms for that expressed purpose.

There is also a sizable portion of the population that believe artificial trees are more environmentally responsible than using a live tree. My personal opinion is this is a fairly small factor in most people’s tree buying decisions but the question persists and seems to get a lot of media play. The American Christmas Tree Association (a trade group that represents artificial tree retailers NOT tree growers) commissioned a life cycle analysis (LCA), which estimated cradle-to-grave carbon footprints for real and fake trees. The bottom-line of the study is that the impact of both is negligible. The tipping point is how far you drive to get a real tree each year and how long you keep your artificial tree. If you get your real tree close to home or combine getting your real tree with other trips, the carbon footprint of the real tree comes out better.

But if the thought of cutting a real tree is still more than your conscience can bear, there is a third option: a living Christmas tree. Many nurseries and Christmas tree farms offer container-grown or balled-and-burlapped trees that can be planted outdoors after the holidays. There are even companies springing up on the west that specialize in live Christmas tree rentals. These companies bring a tree into your house and then pick it back up after the holiday. Some will offer a certificate that the tree will be planted in a park or national forest after its display.

It was a dark and stormy night

A wild and wooly night for many of us last night. A powerful line of storms moved through the Midwest yesterday afternoon and evening, spawning numerous tornadoes, primarily in Illinois and Indiana. Here in Michigan we were spared the tornadoes but had to cope with a long night of high winds, gusting up to 70 mph along the Lake Michigan lakeshore.

The high winds and heavy rains lead to widespread tree damage and power outages. Dealing with a yard full of damaged trees can be an overwhelming and sickening feeling for homeowners. If you are a homeowner or someone who advises homeowners, there are several good resources on the web to assist with the process of assessing storm damage to trees after a storm.

The National Arbor Day Foundation has a storm recovery website that provides practical tips for dealing with storm damaged trees. The website also includes resources for media including press releases and images that are useful for educating the public on steps to take during storm recovery.

The Minnesota Department of Natural Resources also has useful storm recovery information on their website.

For those dealing with storm damaged trees keep these points in mind:

-Stay at least 25 feet away from any downed power lines and contact local authorities to report downed lines.

-Damaged trees and hanging tree limbs are extremely dangerous. Trees that are damaged in storms often have decay or other hidden defect and can drop without warning. Walk around – not under – damaged trees and limbs. Keep children away from damaged trees.

-If you are unsure if you can safely remove a limb or damaged tree, always err on the side of caution and contact a professional arborist or tree service company.

-Be wary of ‘door-knockers’, individuals that descend on storm-ravaged areas that offer to perform tree clean-up or removal. Reputable, professional tree service companies rarely, if ever, solicit business door to door. Working around damaged trees is dangerous work that requires professional training and equipment. Look for arborists that are insured and certified by the International Society of Arboriculture.

My favorite on-line conifer resources

Posted by Bert Cregg

I just wrapped up putting together a species profile on grand fir (Abies grandis) for Great Lakes Christmas Tree Journal, which is the professional trade publication of the Michigan Christmas Tree Association. I do a lot of articles and presentations on conifers and while I draw on my personal experience and background as much as possible, invariably I’ll need to consult some references. Here are some resources that may come in handy if you need to develop a presentation or article or just want to know more about conifers.

Silvics of North America
Silvics is a forestry term that refers to the “study of the life history and characteristics of forest trees especially as they occur in stands and with particular reference to environmental influences.” Back in the day, just about every forester worth their salt had a weathered and dog-eared copy of Silvics of North America on the bookshelf. Today it is available on-line. Silvics contains lots of basic information about trees species; where they grow, how fast they grow, common best problems, and their genetics. Silvics also includes range maps from Dr. Elbert Little, which are a handy reference when you need to know whether or not a species in native in particular location.

Gymnosperm database
Chris Earle’s website is a botanical tour de force. It covers all gymnosperms, not just conifers but, of course, conifers make up the biggest portion of the site. The Gymnosperm database includes species descriptions for essentially every conifer in the world. Many species descriptions also include images. Earle discusses taxonomy of conifers, which for many species, is taking more plot twists these days than an episode of ‘Law and Order’. There are often interesting tidbits under enthnobotany for many species. Bottom line, you can look up just about any conifer species you know on the database and learn something you didn’t know.

American Conifer Society Database
The previous two resources deal primarily with conifers in their native environment. The ACS is dedicated to the Horticultural aspects of conifers. The ACS database includes hundreds of species and thousands of cultivars. For Picea abies alone the database includes over 200 cultivars. For each cultivar the site presents information on hardiness zone, growth rate, form, color and other characteristics. Many descriptions also include photos.

For Mulch

Posted by Bert Cregg

Just a quick note up front that today’s post is a little data heavy, so if you’re still adjusting to this weekend’s time change; be advised.

A few weeks back Jim Urban wrote a post entitled ‘Against mulch’ on the Deep Root blog. The principle reasons he cited for his position were: 1) Mulch floats and can clog drains and releases “lots of phosphorus” as it breaks down, and 2) work by Gilman et al. that suggest that mulch does not reduce evapo-transpiration. We discussed the Gilman et al. paper ad nauseum here already so I’ll stick to the other points.

Most organic mulches float, it’s true. However, if mulch is repeatedly washing from a bed into a drain this suggests a problem with the design as much as anything. Second, I’m not sure what constitutes “lots of phosphorus”. Branch and stem tissue of hardwood trees is about 0.1% P. If we use just the bark as mulch, the P concentration is about 0.2 to 0.3%. Is that ‘lots of phosphorus”? I don’t know. I suppose if you put enough it down and allow it wash into a drain it could be.

So let’s stick to what we do know about landscape mulch. Linda has written the most comprehensive review of mulch out there and it demonstrates the benefits of mulch. Nevertheless I’d like to add some recent observations of my own to the discussion. These come from follow-up measurement on some studies that we have already published on shrubs and conifers. But I think our new data are important because they demonstrate the long-term benefits of much on tree and shrub growth.

2006 Conifer study. In 2006 we installed a trial to compare several different weed control strategies for newly planted conifers. Weed control, either by hand, Vis-pore mulch mats or 3” of coarse wood chips, dramatically increased tree survival.

After 8 growing seasons, trees that had the wood chip mulch or mulch mats had significantly greater caliper than trees that were not mulched.

2004 shrub study. In another trial we compared the effect of various mulch types (wood chips, pine bark, hardwood bark) on growth of common landscape shrubs (golden globe arborvitae, Runyan yew, ‘Tardiva’ hydrangea, cranberrybush viburnum, and arrowwood viburnum). We re-measured heights of the shrubs study a couple of weeks ago (nine growing seasons after installation). To keep things simple here I’ve lumped the mulches together and simply compared mulched vs. un-mulched.

After nine years mulching increased height growth for all shrubs except the arborvitae.

Even more interesting is that the growth benefit of mulch extends beyond the establishment phase. If we start at age 4 and look at the relative growth rate for the past five years (i.e., growth increment for past 5 years / height at 4 years) we see that mulch continues to provide a growth advantage for all shrubs except the arbs.

As I said at the outset, a little data heavy today but I think this is an import point. There is a lot of discussion these days about proper planting techniques but I think after-planting care often gets overlooked and mulching is an important part of that. That’s why I’m for much.

R U nuts?

One of the things that comes along with having an extension appointment at a major university is I get lots of calls and e-mails from homeowners on a never-ending list of sometimes bizarre tree topics. Technically, my extension responsibilities are related dealing with professionals; such as arborists and nursery and Christmas tree growers, but the ‘consumer horticulture’ calls still find me. Last week I received a voice-mail message from an excited gentleman speaking at a decibel level somewhere between rock concert and jet plane take-off. From the disjointed and rambling message I could tell the gentleman was elderly and maybe disoriented or had just had a few. After identifying himself he indicated that he wanted to learn where he could find a “pine-nut tree”. Although he didn’t give it, I knew the man’s location from his area code. A legitimate response to such calls is to redirect them to the individual’s local extension office, but I hate getting the runaround as much as the next person, so I usually respond when it’s something I can help with and in this case I could.

I dialed the number and the gentleman picked up right away. He sounded just as he did in the voice mail; gregarious, slightly rambling, and VERY LOUD. His story, however, made me glad I called back. His father had emigrated from Lebanon many years ago and he remembered how his dad had always reminisced about eating pine nuts in the Old Country. For years he had wanted to plant a “pine nut tree” in memory of his dad. The problem was every time he went to a nursery and asked for a “pine nut tree”, nobody knew what he was talking about.

Pine nuts. Photo: Paul Goyette – Wikimedia commons

Pinus pinea cone. Photo: Luis Fernandez Garcia – Wikimedia commons

I explained to him that the pine nuts his father cherished were from stone pine (Pinus pinea) trees, which are the pine nuts (pignoles) favored for making pesto. In the US, the pine nuts that are sold commercially usually come from pinyon pine (Pinus edulis), which is native the southwestern US. Unfortunately, neither of those trees will grow in the Upper Midwest, where he lives. I pointed out that there are many other pine trees that produce edible nuts – the main reason those two species are widely used is because they produce very large nuts making them relatively easy to harvest. In fact, there are about 20 species of pine that produce seeds large enough that harvesting the nuts is worthwhile. Two pine species that produce edible nuts and grow well in our area are Korean pine (Pinus koraiensis) and Swiss stone pine (Pinus cembra). I include both in my recommendations for alternative conifers for Michigan. I gave the gentleman some information on nurseries in his area that I knew carried those trees and he was excited to have some direction on his quest to renew his father’s memory.

Korean pine (Pinus koraiensis) at the University of Minnesota Landscape Arboretum

Swiss stone pine (Pinus cembra) at Hidden Lake Gardens in southeaster Michigan.

Sidenote: The heartbreak of ‘Pine mouth’.

Have you ever experienced a bitter or metallic taste that persisted for days, even weeks, after eating pine nuts? Then you’ve likely experienced Pine Nut Syndrome or ‘Pine mouth’. The cause of the disorder is not completely known, but research by an industrious graduate student in the Netherlands suggests that nuts from certain pines; particularly an Asian pine, Pinus armandii, are most likely to cause the issue. So, if you are a pine nut fancier, learn what you can about your source. Pine nuts supplies can be cyclical since pine nut crops are often subject to biennial bearing. Soaring prices during poor supply years provide incentive for inferior nuts to work their way into the market.

Let’s get (soil) physical…

We’ve had quite a bit of discussion this past week on the FaceBook page regarding Kelly Norris’s article in Fine Gardening on dealing with clay soils. While Kelly’s article mainly addressed selecting plants for heavy soils, there was a side-bar on cultural approaches to dealing with clays; including the standard advice to avoid adding sand to clays. This advice has been around for years. The first time I recall hearing it was from Dr. Carl Whitcomb when I took his Arboriculture class nearly 30 years ago (Fall 1984 to be exact). The rationale that is usually given is that adding sand to clay is the essentially recipe for concrete. Technically, of course, this is not entirely true since making concrete also requires cement. Nevertheless, trying to amend a clay soil with sand can lead to more problems than it solves. The fundamental issue is not that clay + sand = concrete. After all, there are plenty of highly productive soils in nature that have various ratios of sand and clay and they don’t form concrete. The bigger issue is that tilling a clay soil (which you’d have to do to incorporate added sand) leads to a loss of soil structure.

So, what is soil structure? Soil structure is a physical property of soil that describes its relatively ability to form aggregates. Unlike soil texture, which can be quantified as percent sand, silt, and clay; structure is a qualitative soil physical property. Common examples of soil structure are granular, platy or blocky.

While we usually think of clay as a negative thing (“Geez Jim, my wife just told me you have clay, I am so sorry…”); a well-structured clay soil can have excellent properties for plant growth. Well-formed clay aggregates (referred to as ‘peds’) in a granular soil can function very much like larger soil particles in terms of water movement and drainage. Soil structure is one of those things you have to experience to understand. About the best description I can come with is that peds in a well-structured granular soil often have the consistency and texture of Grape Nuts cereal.

There are also soils out there that are sometimes referred to a ‘structureless’ soils. These include single-grained soils and massive soils. Single-grained soils are essentially pure sand. In West Michigan these occur near Lake Michigan and are often called ‘blow sands’. We have several seedling nursery operations in these areas. Since there is no clay these soils have almost no nutrient-holding capacity – growers have to manage their fertility almost as it were a soilless system like a hydroponic or aeroponic system. The advantage of growing in these soils is it makes lifting bare-root seedlings easy. Massive soils, on the other hand, are very dense soils where particles do not show any evidence of aggregation. Repeated tillage can result in loss of structure and a soil (or portions of the soil) may show attributes of a massive soil including crusting or formation of hardpan. The example below shows how structure (indicated by % aggregation) is lost through repeated cultivation.

Effect of soil tillage on soil structure. Source (Greacen 1958, Australian J. Ag. Res. 9:129-137).

What can be done to improve or preserve structure? This is a case where less is often better. Natural processes such as freeze-thaw cycles and the action of earthworms and other invertebrates work to loosen soil and create aggregates. The tips in the Norris article (avoid overworking soil and adding organic matter) are essentially the same advice I would give.

A Tree Story

Given my line of work, it’s probably no surprise I’m a sap for tree stories (no pun intended). Last week I was in Nova Scotia for the biennial International Christmas Tree Research and Extension conference. The conference and associated tours provided an opportunity to learn about Christmas tree production in Nova Scotia, one of the leading Christmas tree producing regions of North America. During the conference I also learned about the annual tradition of Nova Scotia’s Tree for Boston.

Each year Nova Scotia, through its Department of Natural Resources, presents a 40’-50’ Christmas tree (balsam fir, white spruce or red spruce) to the city of Boston. The gesture is an annual reminder of Nova Scotia’s gratitude for Boston’s and Massachusetts’ immediate aid and generosity in response to the Great Halifax Explosion of 1917. For those of you, like me, that were not familiar with the story, the Great Halifax Explosion occurred in Halifax Harbor on the morning of December 6, 1917. The French Freighter Mont Blanc, packed with explosives bound for the Allies’ war efforts, collided with another ship and caught fire. The explosion that followed, reported to be the largest man-made explosion of the pre-nuclear era, leveled a large portion of Halifax and neighboring Dartmouth, killing nearly 2,000 people and injuring 9,000 more. Within hours of the massive explosion, the governor of Massachusetts sent two trainloads of relief supplies to the devastated city. As a token of their appreciation, the citizens of Halifax provided Boston with a Christmas tree for Christmas 1917.

The tradition of providing a Tree for Boston was revived 1971 and has become an annual event ever since. While the cynical may deride this as a crass and commercial promotion for tourism and Christmas tree exports, the gratitude and affection of Nova Scotians for Boston seems heartfelt nearly a century after the disaster. And, if nothing else, Nova Scotia’s Tree for Boston serves as a history lesson, at least for those of us in the U.S., on this over-looked chapter of World War I.

How to lie with statistics

I’m attending the American Society for Horticultural Science (ASHS) meeting this week in sunny (and hot) Palm Desert, CA. Tomorrow I will be presenting some of the early results from the SOME-DED-TREES study. For those that are new to the blog, SOME-DED-TREES is the acronym for the Social Media DesigneD TREe Establishment Study. Last year, my students and I established a landscape tree study in which the treatments were suggested by Garden Professor’s blog readers. Actually, we ended up installing two studies: one to look at fertilization at planting and one to look at impacts of mulching at planting. The trees were ‘Bloodgood’ planetrees grown in 25 gallon containers. In each study we divided the trees into three root treatments: We “shaved” the outer roots to eliminate circling roots; we “teased” apart the circling roots; or we just planted the trees as is (or “Pop and drop” to use Linda’s vernacular).

I reported some of the results of the mulch study here on the blog last fall and will include some of those data in my talk tomorrow. I am also presenting some of the data from the fertilizer portion of the study. One of the ways we assessed fertilizer response is by using a device known as a SPAD meter.

SPAD meters have been around for a while and they are very useful. The device measures light transmittance through a leaf, which is highly correlated with leaf chlorophyll content. Chlorophyll content, in turn, is highly dependent on foliar nutrition so SPAD readings often provide a useful indicator of plant nutrient status.

Here at the meeting I am using my laptop, which means I am without my usual statistical and graphing software. So in order to plot some of the data for my talk I am relying on Excel. This gets me to “How to lie with statistics.” When I calculated the means for this June’s SPAD chlorophyll index values this is the chart I got. Looks like a pretty impressive response to fertilizer, doesn’t it?

SPAD chlorophyll index of Planetrees fertilized at plant (Fert) and control trees (No).

The problem is the scale. Note that by default, Excel truncated the scale on the y axis to values between 28 and 36. This is a big no-no in scientific circles. Graphs scales should include zero or show if break if there is some reason the range needs to be truncated. The reason truncating the scale is a no-no, as shown here, is that it makes differences look proportionately larger than they really are. Advertisers use this trick all the time. Next time you see a bar chart in a sales brochure or magazine ad, look that the scale – bet it doesn’t go to zero.

Let’s look at the chart after I re-scale it. It still looks like there’s still something going on with fertilizer, but it doesn’t make you go, “Whoa!” like the first chart.

SPAD chlorophyll index of Planetrees fertilized at plant (Fert) and control trees (No).

As it turns out, there is a statistically significant effect of fertilizer on the June SPAD values. However, this effect essentially disappeared by the time we re-assessed the trees three weeks later. Here’s the final version of the data as it will appear in my ASHS talk tomorrow.

This brings up another issue we face in this kind of work; statistical significance versus biological or practical significance. The ‘Fert: p<0.01’ on the slide indicates there is a 99% probability that the difference in the mean SPAD values between Fertilized and Non-fertilized trees on June 17 is not due to random chance or error. But as the leaves continue to mature this effect essentially disappears. Could the early season boost in nutrition be enough to give these trees an edge in the long run? Possibly, but I wouldn’t say likely. To date we have not seen any effects of fertilizer on growth but it’s still relatively early in the game. Tree growth is cumulative and effects that may be too subtle to detect early on may turn out to be significant later on. Stay tuned.

Brace yourself

The photo below (graciously sent to me by former MSU Extension Educator Jennie Stanger) graphically illustrates the importance of removing ALL staking and supporting materials from trees once they are established.

Just a matter of time (Photo: Jennie Stanger)

In this case the stakes were removed but the strapping material was left around the tree. Since this is a spruce, Jennie supposes no one wanted the prickly job of wading into the center of the tree to take off the strap. Eventually the trunk was girdled and when the area recently experienced some heavy thunderstorms, the weak spot on the tree was exposed.

Stately evergreen to mangled mess (Photo Jennie Stanger)

As a general rule we recommend that all staking and support materials are removed within two years, preferably one year. This type of damage is one of the prime reasons: after two years who is likely to remember that there is still strapping left on the tree?

The heartbreak of ‘Carrot-top’ syndrome

The perk of participating in a blog is you get a platform to vent on your pet peeves. Recently I’ve seen several classic examples of ‘Carrot-top’ syndrome. No, I’m not talking about the red-headed comic; though he tends to annoy me too.

Annoying Carrot-top #1.

The ‘Carrot-top’ I’m referring to occurs when white pine trees are sheared as Christmas trees but then planted as landscape trees. The typical result is that the side and lower branches remain suppressed while the terminals go crazy. I’m not sure why syndrome occurs in white pines and not other trees; it may be related to vigor of white pines and how hard the growers have to shear them to keep them in shape.

Annoying Carrot-top #2.

I love my friends in the nursery and Christmas tree industries and they work hard to grow quality trees, but this is one practice I’d like to see end. And, to be fair, they are giving customers what they want. If we set up a survey at a garden center and placed a 7’ sheared white pine next to a 7’ white pine that had been minimally pruned, 19 out of 20 people would take the tree that had been sheared to look like a Christmas tree. However, this is truly a case where less is more.