Bert Cregg

Will cocoa mulch kill my dog?

Recently I was asked to comment about a rash of e-mails floating around cyber-space concerning the toxicity to dogs of mulch made from crushed cocoa bean hulls. Cocoa mulch is by-product of cocoa production. The dark brown mulch is aesthetically and aromatically pleasing, giving the garden a rich, chocolately scent. Since theobromine, a naturally occurring compound in chocolate is toxic to dogs, the internet is now filled with cyber-legends of dogs eating cocoa mulch and keeling over dead.

According to an article published in the Journal of the American Veterinary Medical Association (JAVM June 1, 2006 p. 1644), cocoa bean husks can contain up to 2.98% theobromine. The JAVN article state “no reports of lethal toxicosis from ingesting this mulch have been filed with the ASPCA Poison Control Center this year (2006). In 2004 and 2005, 16 reports of single exposure to the mulch were received, none resulting in death.”

The ASPCA posts this comment regarding cocoa mulch on its website:
“Dogs consuming enough cocoa bean shell mulch could potentially develop signs similar to that of chocolate poisoning, including vomiting and diarrhea. In cases where very large amounts of mulch have been consumed, muscle tremors and other more serious neurological signs could occur. To date, the ASPCA Animal Poison Control Center has not received any cases involving animal deaths due to cocoa mulch ingestion. One key point to remember is that some dogs, particularly those with indiscriminate eating habits, can be attracted to any organic matter. Therefore, if you have a dog with such eating habits, it is important you do not leave him unsupervised or allow him into areas where such materials are being used.”

It should be noted that processed cocoa mulch may contain much lower concentrations and some manufacturers market cocoa mulch that is ‘Pet safe’. Consumers should look for products that are tested and certified theobromine free.

As always, I stand by my recommendation to use locally processed wood products such as ground hardwood bark and ground pine bark. Plants grow well in these mulches, which are typically among the most cost-effective and natural looking (to me, at least) mulches available, and they are renewable and help support your local economy.

The World According to Chub

Following up on Holly’s theme of “I can’t believe I get paid to do this”, last Wednesday I participated in a walk-through and inspection of the Justin ‘Chub’ Harper Collection of Dwarf and Rare conifers at MSU’s Hidden Lake Gardens in south central Michigan. The Harper collection is widely regarded as one of the premier collections of rare and unusual conifers in the world.

Harper Conifer Collection with fall color background. Photo: Jack Wikle.

A little background: Chub Harper was the former grounds supervisor for John Deere’s world headquarters in Moline, IL, an avid plant collector, and a founding member of the American Conifer Society (ACS). He acquired hundreds of rare and unusual conifer specimens around his home and eventually had to lease a nearby lot for the overflow – demonstrating that ACS also stands for ‘Addicted Conifer Syndrome’. In the early 1980’s Chub donated 300 conifers to Hidden Lake Gardens to establish the Harper collection. All of the plants were balled and burlapped by hand and shipped in three semis to Michigan. Chub continued to add plants to the collection and today the collection includes over 500 accessions.

Chamaecyparis pisifera ‘Filifera aurea’

I met Chub about 8 years ago and with his guidance and inspiration started a series of ‘Conifer Corner’ articles in the Michigan Nursery and Landscape Michigan Landscape magazine. (visit my faculty page for .pdf’s of some sample articles http://www.hrt.msu.edu/bert-cregg/pg5). Once or twice a year Chub would travel from Moline to Michigan to inspect the collection along with members of his conifer posse. To me, the most impressive thing about the walk-throughs was how absolutely ruthless Chub was in disposing of under-performing plants or plants with continual pest problems. “Time for that thing to take a ride on the chipper truck” was a favorite Chub-ism. Hidden Lake Gardens has a garden staff that could spray pesticides or prune away dead material regularly; but Chub wanted none of it. This is not to say that Chub was into organic gardening; as far as I know he had no particular aversion to chemicals. Rather, he felt the mission of the collection was education and that maintaining plants in an artificially superior condition would mislead the public into thinking some conifers were better suited than they actually were.

The Conifer posse at the 2007 walk-through. Chub Harper is 3rd from left, back row.

Chub passed away unexpectedly earlier this year and last Wednesday’s walk-through was the first evaluation of the collection without him. The conifer posse carried on, led by former ACS President Dennis Groh; Chub’s longtime friend Jack Wikle; and Sam Lovall, the landscape architect who developed the original design for the collection. We found homes in the collection for several new specimens including an Abies concolor ‘Charmin’ Chub’ and condemned a few underachievers to a ride on the chipper truck. Chub left many legacies; the most obvious and tangible is the Harper Collection and the staggering generosity it represents. Imagine dedicating half your life to acquiring and cultivating a world-class collection and then simply giving it away. Just as important, however, is the legacy he left with those who knew him, who felt his passion for conifers, and were inspired by him.

Pinus parviflora ‘Cleary’

Carrot-top syndrome in white pine

I know a few folks out there are starting to believe that I’m just an apologist for the nursery industry. While it’s true most of the nursery people with whom I work are hard-working folks trying to do their best to run a successful business and produce a quality crop, there are certainly some issues out there and I’ve got my share of pet peeves. One of the things really that chafes my heiney is what I refer to as “Carrot-top” syndrome in eastern white pine (Pinus strobus). White pine is one of the most commonly planted conifers in this part of the world. White pine is native throughout much of the eastern US and is an extremely fast growing tree that makes a good ornamental when planted on the right place with room to grow. It is also widely grown as a Christmas tree in the Upper Midwest as well and therein lies the rub. Many nursery producers also grow Christmas trees and many Christmas tree growers also dig nursery stock. The result? White pines that have been heavily sheared as Christmas trees end up planted as landscape trees. Once in the landscape, the upper portions of the trees will quickly resume rapid growth, with some shoots growing 2’ to 3’ or more per year; while the side shoots that had been repeatedly sheared barely grow at all. After a couple of years the net result is neatly trimmed Christmas tree with a wooly beast growing out of its top. What’s the solution? Ideally producers should identify which portion of their trees will be sold as Christmas trees and which are destined for the landscape trade. Christmas trees can be sheared to meet demands of that market while landscape trees can be pruned much more lightly to maintain a single leader and conical form but keep obvious layers of whorls. The dilemma, of course, is that growers don’t always know which trees will end up and the Christmas tree lot and which will be dug for the nursery trade. The other, more challenging problem is that, given a choice, 99 out of 100 garden consumers will choose the neat-looking Christmas tree for the landscape, unaware of the wooly mess that’s about to be unleashed in their yard. The solution? Education on both sides; making growers aware of the issue and making consumers realize that the only way to have a natural-looking white pine in your yard is to start with a natural-looking white pine.

Heavily sheared pines will retain the outline from from shearing for years while the top rages out of control.

Should I boycott cypress mulch?

It’s hard to think of mulch as a controversial topic but, as with most things these days, we find people on both sides of an issue. And, as with most things these days, some of opinions are based on substance, others are not. In the southern U.S. some environmental groups are advocating a boycott of cypress mulch.

Cypress mulch is derived from baldcypress and pond cypress, which grow in ecologically sensitive wetlands in the Southeast. Cypress wood is highly valued for is natural decay resistance. Florida and Louisiana are the leading states for cypress harvesting for timber and other products. In Louisiana it is unclear if cypress is logged solely for mulch but cypress harvesting for mulch does occur in Florida. According to Dr. Jim Chambers, professor of Forestry at Louisiana State University and Chair of a governor’s science panel on forested wetlands in Louisiana, cypress mulch production is a sensitive issue. “Many of our cypress-tupelo forests are in a severe state of decline. As you can imagine, these forests are very important to south Louisiana for many reasons. Areas permanently flooded, areas that are flooded for substantial parts of the growing season, and areas subjected to salt water input cannot regenerate. The amount of forested areas with these conditions continues to increase as subsidence increases, coastal wetlands are eroded by storms and human impacts on hydrology continue to degrade many sites.”

The inability to regenerate new stands of cypress is an important concern and calls into question the sustainability of cypress harvesting on these sites. Chambers is working with environmental groups and others to develop a process to certify that mulch is produced from sustainable forest harvest operations

Another issue related to cypress mulch is a claim that is circulating in parts of Michigan (and perhaps elsewhere) that cypress mulch is linked to cancer. I conducted a search of the National Library of Medicine and National Institutes of Health literature database (www.pubmed.gov) on ‘cypress’ and ‘cancer’. The only hits I found were related to studies looking at falsecypress (Chamacyparis) extracts for anti-cancer properties, similar to taxol. The claims of cypress mulch and cancer may be an amalgam of the environmental concerns over cypress harvesting discussed above and concerns over use of mulch derived from CCA (chromated copper arsenate) treated wood, which is used for decking and other uses similar to cypress. Research has shown that leachate from mulch containing CCA treated wood can have elevated levels of arsenic and metals above established health standards.

We all know Linda’s fondness for wood chips as mulch. My personal favorite is ground red pine bark for its durability and natural appearance. The key is to look for renewable mulch products that are locally sourced.

The Flap Over Burlap

This month’s issue of the Oregon Association of Nursery’s Digger magazine includes the second part of a two-part article on urban foresters’ perspectives on nursery stock. It was interesting to note that some urban foresters felt they were in a quandary because their specs require removal of burlap from B&B trees, yet many nurseries will void their warranty if burlap is removed from the root ball.

Removing burlap from B&B trees is a practice that is widely recommended, yet there is little, if any, data to support it. The logic, of course, is that burlap will prevent root egress into the surrounding soil after planting. But is this really the case? We conducted a study a couple of years ago using 3” caliper B&B green and white ash trees as part of a trial on the movement of a systemic insecticide (imidacloprid) for treatment for emerald Ash Borer. Since we were using radioactive carbon-14 as a tracer, safety regulation required us to keep the trees contained. The trees were dug with a 36” tree spade and placed in burlap-lined wire baskets by a local nursery (Discount Trees. Inc.) using their standard procedures. For the study we placed the root balls in large orchard boxes backfilled with top soil. We removed all ropes and the top of the burlap. The trees were used for a study that lasted two growing seasons. At the end of the second season we conducted whole tree harvests on a sub-sample of the trees. My vision for the root system harvest was that we would simply chain up the baskets and pop the trees out of the boxes; the burlap would help contain the roots, right? Wrong. Separating the root balls from the boxes became a major ordeal that involved a whole lotta shakin’ with the front-end loader. Once the root balls were finally extracted it was obvious that the burlap provided little resistance to root egress into the surrounding soil.

My former grad student, Grant Jones. “He said it would come out easier than that…”

Mike Kuhns at Utah State University conducted a trial several years ago (J. Arbor. 23:1-7) in which he observed a similar phenomenon. Mike compared root egress of B&B maples with burlap removed versus a single or double layer of burlap by calculating a RTRATIO which was based on the amount of the total root system weight that was found outside the original root ball. There was no difference in the RTRATIO between trees with single burlap and trees without burlap at any date during the 2-year study. Double burlap decreased RTRATIO initially but there was no difference by the end of the study. Annela et al. (Arb. & Urb. For. 34:200-203) compared various growth parameters of baldcypress, plane tree, and freemani maples transplanted bare-root or B&B with only the top of the burlap removed. After two years the only statistically significant difference was an increase in shoot growth for the B&B maples.

So what does it all mean? My personal opinion is that when it comes to establishing trees in the landscape we spend way too much time worrying about trivial matters like this. (Digging a planting hole 3X the width of the root ball and amending backfill are others but we’ll save those for another post). Matching species to site, quality planting stock, and proper after transplant care – especially mulching and irrigation – are way more important but still neglected. If we plant quality plants in the right place and take care of them properly the first two years after planting we would eliminate 80%+ of the transplant issues I see. Burlap or no is a tempest in teapot.

EverGreen or EverYellow?

In last week’s post I mentioned that many tree problems can be difficult to diagnose and require a thorough inspection and site analysis to get to the root of the problem. In contrast, a recent issue that has generated a lot of calls is easy to explain and is not a cause for major concern. Many homeowners and others are alarmed that needles on their white pines are turning bright yellow.

“Is my pine dying?”

The key in assessing this situation is looking at which needles are turning color. Except for southern pines, most conifers produce only one, single flush of new needles each spring. Because of this, we can work our way down a shoot and tell when each group of needles was formed. The outermost needles were formed in the current year, needles in the next internode were formed the year before, needles formed in the next internode were formed the year before that, and so on. Most evergreen conifers keep their needles for 3-6 years and then the needles senesce and fall off. The longest-lived needles, perhaps not surprisingly belong to bristlecone pines, which are also the longest living trees on earth. Bristlecone pines, the oldest of which is over 4,500 years old, have needles that persist for 13 to 17 years. But I digress, back to the white pine. White pine needles last 2 or 3 years. Each fall, many of the previous year’s needles turn yellow and senesce. Since the needles often turn bright yellow and almost half the needles on the tree are affected it can certainly grab attention. As long as only older needles are turning, the process is natural and there’s no need for concern. On the other hand, if this year’s needles are dropping that’s another issue and warrant further investigation.

White pines don’t keep their needles very long. As long as this year’s needles aren’t senescing, the tree should be OK.

Pining to learn more about conifers? The Gymnosperm database http://www.conifers.org/ is an awesome and authoritative site that has information on just about every conifer known to science.

Support your local arborist

A couple of weeks ago I was interviewed for the local paper about this year’s fall color. It’s pretty standard fare around these parts; newspapers, AAA, and so on want to know if we’re going to have good fall color, will it be early, will it last long. I mentioned to the reporter that we’re seeing a lot of early fall color in the maples around mid-Michigan, in contrast to the northern part of the state, which appears to be running a little late. The question of course, is why. I noted even though this summer was relatively cool, trees have been stressed the past several years and some pests, such as clearwing borers, that might not normally be major problems may be taking advantage of the situation. After the article appeared in the Lansing paper, it was picked up by the Chicago Tribune and USA Today (must’ve been a slow news day). Since then my volume of “What’s wrong with my tree?”calls and e-mails has skyrocketed. Depending on how busy I am I usually make an effort try to respond to homeowner calls. A few issues, such as tar spot on maple, can be diagnosed sight unseen; “My maple has little black blotches on the leaves that look like tar spots”. Most serious tree problems, however, require a site inspection in order to fully evaluate and diagnose the problem.

If callers and e-mailers really want to get to the bottom of their tree problems I usually tell them to contact a professional, certified arborist in their area. The International Society of Arboriculture (ISA) provides training and certification for professional arborists. In order to be certified, arborists must meet certification standards and take continuing training to maintain their certification. Being an arborist is a tough job. And the business of being an arborist is made tougher by the low barriers to entry. Anyone can buy a chainsaw, slap a magnetic sign on the side a pickup, and advertise himself or herself as a tree service. Quality, professional arborists have to pay for training, insurance, bonding, up to date equipment, and proper safety gear for all employees. It’s not a very level playing field. But for the client that is looking to save the oak tree that Grandpa planted when he moved into the house after the war, the knowledge and expertise of a professional is far preferable to the chainsaw of Joe’s Fly-by-night tree service.

To find a professional arborist in your area look in the Yellow pages under Tree Services and look for arborists that are ISA certified and insured. Also the ISA has a search feature on it’s website that enables homeowners to find an arborist based on their zip code.

Baring it all, again.

Earlier in this blog we had a rather robust discussion about the merits of transplanting trees bare-root. Bare-root transplanting has had a renaissance in arboricultural circles, based in large part on the work of Dr. Nina Bassuk and her colleagues at the Urban Horticulture Institute at Cornell.

As our bloggers noted, transplanting trees bare-root has advantages over balled and burlap trees (larger portion of the root system stays with the tree) and over container-grown trees (more natural root system development). One disadvantage of bare-root trees is the need to protect roots from desiccation during storage and handling. Also, some trees respond better to bare-root treatment than others. Nevertheless, I think we will continue to see increased interest in bare-root planting. One notable trend is planting relatively large-caliper (4” and larger) trees bare-root. This phenomenon has coincided with the development of the air spade, a tool which produces powerful a jet of air that allows arborists or nursery workers to carefully excavate an entire root system with minimal disturbance. Unlike digging a tree with a traditional tree spade, the air spade allows nursery workers to maintain virtually the entire root system when lifting a tree. Last week, my esteemed colleague, Dr. Tom Fernandez, and his Nursery Management class at MSU worked with Paul Swartz, MSU campus arborist, to lift a 10” caliper weeping white pine from our campus nursery. Members of the class took turns using the air spade to excavate the entire root system of the pine. Since the class is divided into lab sections that meet throughout the week the process was spread over several days. After each lab period exposed roots were covered with wet burlap to prevent drying. By the end of the week the tree was ready for lifting and was transported via flatbed truck to its new home at the front entrance to the MSU Horticulture Teaching and Research Center. Paul Swartz reports that he has successfully used the air spade to move several large specimens on campus and the technique is especially useful for moving trees from tight spots that can’t be reached with a mechanical spade. As more and more arborists acquire air spades look for this technique to become more common.

NOTE: Photos courtesey of Dr. Tom Fernandez.

The air spade uses a stream of compressed air to excavate roots.

Note the extent of the root system. A 90″ mechanical spade would have missed at least half the roots of the tree.

Once the roots are excavated the tree is ready for lifting.

The pine resting comfortably at its new home.

Shoot your favorite ash

One of the biggest issues facing urban and community forestry in the eastern half of North America is the Emerald Ash Borer (EAB). As most people are aware, EAB was accidentally introduced in Michigan some time in the late 1990’s. By 2002 when the insect was found and identified, thousands of ash trees in and around Detroit were dead or dying. Since then the insect has continued to spread, partly by natural dispersal but also by hitchhiking on logs and firewood. As of July 2009, EAB now occurs in 13 states and 2 Canadian provinces. To date, researchers have not found any indication of resistance to EAB in North American ashes. This includes green ash and white ash. Based on our current understanding of the insect, EAB has the potential effectively eliminate the ash genus from North America, similar to effect of chestnut blight on American chestnut or Dutch elm disease on American elms. To help stave off the demise of ash to EAB a veritable army of university and government researchers are conducting wide array of trials to identify chemical or biological controls that can save ashes. Several insecticides can be effective but so far are only feasible for use on high-value landscape trees due to the cost of application and the need to re-apply treatments every 1-3 years depending on the chemical.

To help build awareness of the destructive potential of EAB and the impact of losing ashes in North America, I invite readers of the Garden Professor’s blog to share photos of their favorite ash. Photos can be e-mailed to me @ cregg@msu.edu and I will post them on the blog. Include any pertinent information about the tree(s). To get things started I have included photos of ash trees surrounding the Gateway arch in St. Louis. In the early 1970’s over 500 ‘Rosehill’ white ash trees were planted along the sidewalks in the park area surrounding the arch, which was completed in 1967. The ash trees frame the famous ‘Gateway to the West’ and provide shade to cool visitors during St. Louis’s sweltering summers. Unfortunately, the ashes may ultimately serve as a cautionary tale of the perils of monoculture in landscape design if they are lost to EAB. The National Park Service, which manages the Gateway Monument grounds has begun to plant new trees from a variety of species. However it will be years before those trees will be anywhere near the size of the existing ash trees. To date, EAB has only been found in Missouri in an isolated outbreak in the southeast corner of the state but the insect has a firm foothold in Illinois and is moving westward. The ashes in the Gateway monument are being monitored for EAB and presumably the Park Service will begin treating the trees with trunk injections of systemic insecticide if EAB are detected in or near the Monument.
Ash trees frame the Gateway to the West

Over 500 'Rosehill' ash trees line the walkways at the Gateway National Monument

Another look at TreeGators

Following up on Linda’s earlier comments about potential problems with TreeGators, my summer interns and I did a random spot check of about 150 TreeGators currently in use on the MSU campus. As background, MSU Landscape Services plants about 1,200 trees and shrubs each year. All newly-planted trees which are not on an automatic irrigation system are fitted with one or two TreeGators, which are filled from a water wagon every week or every two weeks, depending on weather. Conifers and multi-stemmed trees are fitted with Tree-Tubes, another style of irrigation bag that fits like an inner-tube around the base of a tree. At MSU irrigation bags are usually left on trees during the first growing season. Presnetly there are over 1,000 irrigation bags in use on the MSU campus.

During our spot-check, we found few items I would consider to be a major concern. We found 25 trees with mold or saprophytic fungi growing in the mulch under the bags. While unsightly, these are unlikely to cause major tree problems and will be gone once the bags are removed and the mulch is exposed to air. All but a handful of the bags had drained properly and therefore the trunks on most of the trees were dry – eliminating the potential problems that Linda noted about the trunks remaining constantly wet. TreeGators are designed to drain in 4-5 hours. Therefore, on a once every two weeks or once a week filling-cycle, they should be full only 1.5% to 3% of the time. TreeGators that are not draining between fill-ups should be checked for clogs and have a new hole punched, if needed.

It is worth noting that the dark protected space between the irrigation bag and the trunk can provide habitat for various organisms. We found an assortment or earwigs, spiders, and millipedes; plus one tree frog and one dead bird. The major concern that we found, however, were gypsy moth egg masses (photo 1), which occurred on 14 trees. Gypsy moths, which are serious defoliators of trees in the eastern US, like to lay their egg masses in protected locations on tree trunks so the inside of the Gator bags makes a handy hideout. Once found, egg masses are fairly easy to remove, though killing the eggs takes some effort.

While there is a potential for pests to hide out under irrigation bags, I think the benefits of irrigating with TreeGators outweigh the potential negatives. This is especially true in our heavy Midwestern soils where it is impossible to deliver any meaningful amount of water to a newly planted tree in a reasonable time without run-off. MSU Campus Arborist Paul Swartz reported less than 0.5% mortality out of over 1,000 newly planted trees on campus last year. The high success rate is attributable to good overall tree management by Landscape Services, including supplemental irrigation using the irrigation bags. The take home message from our survey is that tree care workers need to check bags at each filling to ensure that bags are draining properly and to lift up the bags and inspect for signs of pests or other issues.

TreeGators on MSU Campus

Tree frog inside TreeGator

TreeGators should drain in 4-5 hours when working properly.

Cause for concern. Gypsy moth egg mass on trunk.