The Garden Professors™

Graft and corruption

It’s election season – but that’s not why I’m doing a blog on “graft and corruption.” Instead, let me back up and explain that today I gave a seminar on diagnosing urban tree death. One of my points to the group was the importance of knowing the history of a site – what species were selected, how trees were planted, whether there had been any major construction activity, etc. I thought I’d continue the importance of site history into today’s posting.

Here’s a photo of a street tree – a Prunus spp. (Disclaimer: I am not endorsing a candidate for Mayor of Seattle despite the appearance of a campaign sign in the photo.) It’s a healthy enough specimen, though possibly a bit large for this narrow planting strip:

Several years ago you would have seen a different tree in this same spot:

Now did this weeping cultivar somehow transform into an upright form? Let’s look at this second photo in its entirety:

This reminds me of my favorite childhood book on Greek mythology, which had a great drawing of Athena springing from the head of her father, Zeus. Yes indeed, we are seeing the scion of a grafted tree lose the battle to the rootstock. Rootstocks, by their very nature, are vigorous. If we revisit the first photograph again, this time a little closer, we can see all that remains of the poor scion:

Lesson: if you are using a grafted tree in the landscape, you need to keep the rootstock under control. Grafted trees are probably not good choices for low-maintenance landscapes.

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.

Epicormic mystery solved!

Good morning (at least it is in my time zone)! And welcome to those of you who found us through Blotanical or another blog site. We love seeing the increased participation on our blog.

Since I am a teacher at heart, I was glad to see so much thoughtful discussion over the weekend. Many of you suggested that pruning for vehicular traffic was the trigger for this growth, and it’s true that removing large limbs or heading back branches will result in vigorous epicormic growth. But I cheated on the photo and cropped it above the point of interest. Here’s the entire photo of this tree:

You can doubtlessly see that dark line encircling the trunk just above the two branches with the shoots. Here it is close up:

Venturing around to the back of the tree, we can see the source of this line – neglected staking wire that has now been enveloped by the trunk.

What this wire has done is to girdle the phloem elements, which as you’ll remember from basic plant science, are directly below the bark and the cork cambium. Without functional phloem, nutrients from the crown can’t reach the roots. Since the two lower branches were spared this girdling, they can still transport sugar to the roots, so the tree hasn’t died. But now it’s directing resources (water and nutrients) into the lower branches, where the new epicormic shoots are forming a new, functional (albeit ugly) crown. In time, the original crown will probably fail; there’s already evidence that the trunk is dying:

What could be done with this tree? If the wire were removed or at least cut so that the trunk could pop it apart, there is the possibility that the crown could have been saved. But since the upper trunk already looks severely compromised, it’s probably too late.

As a sad update to this set of photos, the owners had a tree “service” (I use the term loosely) to remove all the epicormic shoots from the lower limbs! I will let you know when and if the whole thing fails.

Oh, and gold stars to all who participated in the quiz!

Quiz time!

One of the things we Garden Professors can do is give tests! And the nice thing is you don’t get penalized for being wrong. So this will be my inaugural Plant Puzzler.

Below is a photo of a tree with epicormic shoots on its two lower branches. Epicormic shoots are vigorous, upright branches that have more of a juvenile than mature appearance. They often appear when a plant has been stressed, perhaps by overpruning, or maybe the roots were damaged by construction:

So here is your test question. Why are these epicormic shoots primarily (if not exclusively) on the two lower branches, and not elsewhere in the crown? (You can’t see the top of the tree, but I promise there are no epicormic shoots up there.) And what evidence would confirm your diagnosis? While there is only one correct answer for this particular tree, let’s see how many possibilities you can come up with.

Answers and more pictures next week!

My Least Favorite Pesticide

People often ask me about the most dangerous pesticides — the ones which they should be careful to avoid. There are lots to choose from: Di-syston (aka disulfoton) is really bad. Rotenone has some potential problems that make it scary, as does copper sulfate. But for my money the worst thing out there is something that isn’t even supposed to be used as a pesticide (at least not anymore) but which finds its way into our gardens thanks to recommendations from people like Jerry Baker: Tobacco.

Despite its obviously “natural” origins, tobacco isn’t allowed by organic growers because of its drawbacks which I’ll mention below, but because it finds its way into so many “how-to” books it’s definitely worth knowing about this beast.

It’s easy to buy chewing tobacco, mix it with a little water, and apply it to whatever aphids or other insects that you see. What’s even better is that tobacco really does work (just like Jerry says!). In fact, for some things it works great. For example, I’ve tried all kinds of barriers against slugs, and tobacco is the one that works the best, hands down — copper is kinda OK, diatomaceous earth takes a while but works fine — but man, tobacco really throws slugs for a loop. Watching a slug try to go through a pile of tobacco is terrible (and yet morbidly entertaining!) First, the slug approaches the tobacco at a snails pace (the snail is a close relative of the slug!) Then the slug touches the tobacco….and then the fun begins! The slug starts to move really fast — literally mouse walking pace — and then it stops — and then it shakes — and then it dies. This all happens within four minutes. The slugs in the picture below are all dead.

Despite my success I have a hard time recommending tobacco for slugs for two reasons. The first is that it can carry plant diseases which can cause some major problems, and the second is that some dogs like to nibble at the tobacco — and they won’t let you know they’ve nibbled it until you let them back into the house (if you know what I mean)!

When a tobacco spray is used for insects the process is a bit different than just placing tobacco on the ground. First, you mix tobacco with water, let it soak for awhile, filter the water out, and then spray it on the insects. In the old days — the 1800s when this type of spray was popular — they would mix about a pound of tobacco with a gallon of water. Jerry usually recommends much less. The problem with recommending less than this is that at lower concentrations it doesn’t work nearly as well — but you really wouldn’t want to apply more because then the spray starts to get dangerous (because of higher nicotine concentrations). So it’s a catch-22. Don’t underestimate the toxicity of nicotine! Also avoid underestimating the nastiness of the plant viruses that this stuff carries.

So what should you use instead? A good insecticidal soap, or a spray with water are what I like to recommend. If you must use something stronger then look for an insecticide with the active ingredient permethrin and follow the labeled instructions carefully (also make sure that the insect you want to control is on the label — if you can’t identify the insect you’re trying to control, or if that insect isn’t on the label, then don’t use a pesticide). For slugs my favorite pesticide uses the active ingredient iron-phosphate.

Wonderful wood chips

I’m in love…with arborist wood chips. These are not your beauty barks or other packaged mulches, but the chipped branches and leaves fresh from the tree crews. It’s a great way to keep this resource out of the landfill – and don’t even get me started about using this great mulch material for a “biofuel!”

I’ve written about wood chip mulches a lot, but thought today I would post some photos to show you how well they work in suppressing weeds and promoting growth in restoration sites. We published a paper on this in 2005, though we’ve been using them in ornamental and restoration landscapes for about 10 years.

Here’s a recent project: a wetland buffer enhancement was being installed in an area that was covered in Scot’s broom (Cytisus scoparius) and blackberry (Rubus discolor):

We had a brush cutter mow it to the ground, then put a foot of wood chips down. Later, we planted poplar, ash, willow and alder on the site:

We had to keep records, both written and photographic, for the county who monitors wetland projects. So we took photos every year at the same points for comparative purposes. Here’s what part of the site looked like immediately after planting and then after 5 years:

That’s not to say that we haven’t had to battle resurgent blackberries. They migrate over from the wetland itself (which we can’t touch) and tip root. But the increasing shade and competition from the trees has weakened their ability to take over, and the Scot’s broom has been gone for years.

So that’s one reason I love wood chips. I’ll do a follow up some week showing how they can be used in the home landscape.

The joys of arborizing!

It’s Holly’s day…but she’s off playing in a tropical paradise. So because she seems to be of a sunnier disposition than I am, I’ll post happy thoughts today.

One of my favorite pruning techniques, especially for small urban landscapes, is arborizing. This is a way of creating small trees out of large shrubs – and often, a large shrub is as much as a small landscape can handle. Rhododendrons are common landscape plants here in Seattle, and the larger ones lend themselves beautifully to this practice:

As you’ll notice in this example, arborizing not only creates an aesthetically pleasing tree form, but also moves the crown away from vehicular and pedestrian traffic. This protects the plant from damage and enhances access.

This also works wonderfully in landscapes where you would like to have layers of shrubs, rather than one massive plant. Look at this Ceanothus:

Arborizing this shrub not only allows planting additional plants underneath, but also allows some light into the house (note the window in the background).

Fall is generally a good time to prune (after the crowns have gone dormant). It’s easier to see trunk and branch architecture in deciduous trees, and generally places less stress on the plant.

If you’ve arborized shrubs before, which species work well for you? Which ones not so well?

See? I can be a happy blogger!

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.

Chad and Jeff’s Excellent Nursery Adventure

About 3 months after I started my job in Minnesota I hired a technician to help me run the nursery and to manage research plots. His name is Chad and he stands about 6 foot 4, has shoulders that threaten to pop the sides of the skid steer loader whenever he enters it, and he knows his stuff because he needs to (and even if he didn’t know his stuff you’d be scared to tell him that because he looks dangerous with his frightening Fu-Manchu moustache). Currently Chad is responsible for day to day operations in the nursery as well as writing publications. In other words he’s indispensible. When you read a post from me, particularly when it’s regarding nursery or landscape research, you’re usually reading a combination of both of our thoughts.

Over the years Chad and I have seen a lot of nursery stock; some of it good, and some of it bad. Between us we’ve seen poor pruning, unhealthy root systems, pot-bound plants, trees planted in soil that was much too alkaline or acidic for them, trees planted in the wrong zone, trees sold that weren’t close to the size that they were supposed to be, trees that were girdled by critters, root systems completely eaten by voles and even a tree shot with a handgun. I once saw a whole field of Japanese maples topped (basically topping is when you cut horizontally through a trees canopy to give it a flattop – talk about competing leaders and narrow crotch angles!). Seeing that field almost made me cry – A planting worth $20,000 – $30,000 wholesale almost instantly became worth the price of kindling. But we agree that none of that can hold a candle to Sara’s Nursery (Named after the owner’s daughter).

I received a call a few years ago from a nursery in western Wisconsin (which, for those of you who aren’t familiar with this part of the world, is much closer to the Twin Cities than to Madison, WI where the University of Wisconsin is). The caller was very concerned that the plants in the nursery which she had been hired to run were failing. Basically, their leaves were dropping and she couldn’t figure out why. This was even happening to plants that we usually consider “indestructible” like potentilla. I had never heard of such a thing, but it sounded like a soil problem and so I asked her to have some soil tests done and to send me the results. She agreed, but she was distraught and asked me to come and take a look at her operation. I balked at first, but after a few minutes of begging I gave in. I asked Chad if he’d like to join me on a trip to the nursery the next day; he agreed and we were off.

The nursery that we found was a retail operation on a road which was once a major thoroughfare, but had been reduced to a minor highway when the interstate, which ran parallel, had been expanded. Still, it seemed like a pretty good location for a retail nursery in terms of customer traffic. After we parked the car Chad hopped out and began inspecting balled and burlapped evergreens while I joined the manager to look at their container stock. It was a mess. It was the end of summer when we visited, but the leaf drop made it look as though we were in the late fall.

I popped a potentilla out of a container and could find no roots reaching the containers edge. Taking a closer look I quickly discovered one major problem. These were bare root plants planted into containers filled with soil. Soil is almost never a good thing to put into a container because it’s usually too heavy and prevents air from working its way down to the plant’s roots. The gentleman who owned the nursery (not the manager – in most cases she just seemed to do what the owner wanted to do) was a farmer who had decided that it made sense to save money by using this soil which grew his field crops so well. This nursery was buying bare-root plants, popping them into containers filled with field soil, and then selling them at quite a mark-up (by the way, this is considered an unethical practice).

This field soil was obviously a problem, but, while plants usually suffer because of the use of soil in containers, I didn’t think it was likely to cause the carnage that I was seeing. I asked about their fertilizer and watering practices. Both of those seemed reasonable and unlikely to cause a major problem.

Meanwhile, Chad came back to report on the evergreens. Almost all of the evergreens (which showed signs of repeated shearing – good for Christmas trees — not good for the long term health of landscape trees) were missing needles close to the base of the tree and appeared to be suffering somewhat. I thought it might be a water issue, particularly if city water were being used, and asked where it came from. The manager told me that all of their water came from a well on site. In this part of the world we frequently have issues with well water being too alkaline, but it usually doesn’t cause the type of damage that I was seeing here. I filed water away as a possible, but unlikely cause.

I was pretty stumped, as was Chad. Obviously we saw problems, but these just didn’t seem sufficient to cause what we were seeing. The manager offered to show us the potting operation, we followed. The first thing that struck me about the potting shed was that it seemed old, and yet the timbers themselves hardly showed any rot which is kind of unusual. We asked when the shed had been built and the manager indicated that she had reason to believe that the shed had been built in the 1940s or 50s.

We entered the shed and noticed a large pile of what we assumed to be soil. Nothing special. Then our eyes began to adjust to the dim light and we realized that this was no ordinary pile of soil. It was mostly white. We were confused. The first thought that went through my head was “what is this, cocaine?” Then I thought, no, it must be perlite. I looked at Chad. His eyes were big and round. I went over to the pile, poked my finger into it, and then touched it to my tongue.

“What the EXPLICATIVE DELETED is this place?” I asked Chad (OK, I may not have used those exact words, but it was something close). The manager must have overheard.

“Well, it’s a potting shed now, but it was built to store salt for the highway” she responded. “That’s just a pile of leftover salt. We stack our soil against it when it comes in.”

We tested both the soil from the pots and their irrigation water. Both were ridiculously high in salt (and, not coincidentally, sodium levels). In fact, salt levels were high enough in the irrigation water that it would literally burn foliage off of the plants.

Shortly after visiting this nursery Chad became a Buddhist and my beard turned more gray than brown. I can’t swear that it was this nursery that caused these changes, but I can tell you that I haven’t been the same since.

Building a better tree? Not in the long run!

One of the landscape tree production practices that drives me absolutely nuts is heading back trees in the nursery to create “columnar” specimens. It’s easy to find examples of these in Washington state nurseries, like the pathetic oak shown below:

Aesthetics aside, let’s focus on how the tree responds to heading back. The removal of the dominant leader encourages lateral branches below to become more upright; from these laterals, a new leader is selected. This new upright growth habit is highly prized by many landscape architects and urban planners, as such trees fit more neatly into small urban spaces without interfering with vehicle and pedestrian traffic. Sure, it works great for a few years.

Now let’s look at these trees a decade or two later. Branches grow in diameter as well as length. All of these acutely angled branches begin to grow into each other, creating bark inclusions:

What effect do bark inclusions have on the trees? These fused branches are not strongly connected; in fact, they are likely points of branch failure. As these branches become larger and heavier, they can create hazard situations if they are near people or property. What’s happening here in Washington, and probably elsewhere, is that arborists must be hired to prune out some of these branches to reduce the risk of failure and injury.

This…most definitely will lead to this…eventually

I can’t understand why this practice is perceived as “building a better tree.” To me, it looks like creating a maintenance and liability problem down the road.