The Garden Professors™

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.

Bare Root Trees

For the past 11 years I’ve been running a nursery at the University of Minnesota called the TRE (for Teaching, Research, and Extension) nursery where we research all kinds of fun stuff like Dutch elm disease, the dangers of mulching, and what happens when you plant a tree too deeply. One of the most interesting things we’ve done recently, though, is to install Missouri gravel beds into the nursery. Missouri gravel beds are called Missouri gravel beds because they were invented by Chris Starbuck, a professor at Missouri State. He mostly works with gravel beds above the surface of the soil, while here at Minnesota we work with gravel beds below the surface of the soil (the gravel bed below is 60 feet by 10 feet and filled with about 2 feet of pea gravel — we do have a system for recirculating the water — which we sometimes use and sometimes don’t because of clogs, algae buildup, etc.).

We take bare root trees and place them into these beds in spring (when bare root trees are available from nurseries) to encourage root growth and then plant them out into the field later in the season. The amount of beautiful fine roots for transplanting is just incredible, and the resulting plant can be planted bare root any time of year, instead of just spring when bare root plants in our area are usually transplanted.

Now to be a little more specific: I’m a tremendous fan of planting bare root plants, but I’m not a fan of planting larger plants bare root (at least not without Missouri gravel bed treatment), particularly what are known as B&B trees — trees that are harvested and held in a burlap and wire cage, such as those being harvested below from our nursery.

The reason that I don’t like taking a B&B tree and planting it after bare rooting it (by removing all of the burlap as well as the wire cage and then washing off the soil that surrounds the roots) is that, no matter how gently you wash off the roots, fine roots tend to be destroyed. When you harvest a root ball for a larger tree you are removing about 80-90 % of the roots. The additional roots that you remove by washing the ball will often make the tree non-viable. This is something that have I learned from experience with individual trees, as well as from replicated experiments using hedge maples and Turkish filberts. We used trees with a stem diameter of about 2 inches with standard sized root balls for that size tree, washed off the root ball for half (five trees of each species) and planted the other half using our more standard system (we removed the top portion of the burlap and wire, but not the bottom portion so as not to disturb the ball). All of the trees which we bare rooted from B&B died after planting and all that we didn’t bare root lived. This is further supported by some research coming out of the University of Illinois earlier this year by Andrew Koeser (and coauthors) which shows that handling the balls of B&B trees just isn’t that good for them.

So why am I spending so much time with this? Simple, this is an area where researchers disagree. In fact, based on what Linda has written in the past I’ll bet that she disagrees with me. And that’s a good thing. People always want the quick and simple answer, but often there isn’t a quick and simple answer. I can’t deny that sometimes bare-rooting a B&B tree before planting might be a good thing. But I think that, in the majority of cases, it’s a mistake. In terms of containers — We’ve got a big research experiment going on that right now — we’ll have results next year.

Mmmmm…mulch!

It’s a nice sunny September day in Seattle and I’m in my happy place. What better topic to match my mood than mulch?

For those of you not familiar with my fixation on woody mulches, I’ll refer you to an article in MasterGardener Magazine here. Briefly, I am a fan of coarse, chunky organic mulch, particularly arborist wood chips or other chipped material from trees and shrubs.

Rather than send this material off to the landfill, it’s so much better to use it as a protective layer on top of your landscape soil. It’s a cheap, natural way to protect and nourish your plants, and provides a great habitat for beneficial insects and microorganisms.

Practically speaking, how does one move a mountain of mulch? Shovels don’t work well, and compost forks have too much space between tines. My favorite tool is the mulching fork. It’s relatively lightweight, well balanced, and makes quick work of wood chips.

Sometimes you’ll find twigs in your mulch pile, or might have your own woody prunings that you’d like to use as mulch. My second favorite tool is my electric chipper/shredder. It’s powerful enough to deal with small branches and twigs and helps me create a more uniform mulch. Plus, I reuse my yard waste and keep the nutrients on site rather than throwing them away.

I don’t own stock in either of these products (my faculty salary doesn’t exactly allow me to be an investment tycoon). They’re just a few of my favorite things…

A Brief Discussion on the Wisdom of Barberry as Median Plant

We never know who to blame (or, rarely, thank) for roadside or median plantings. State D.O.T.? Local municipality? Subcontractor to either of the previous?

A few years ago, this appeared in the median of the Highway 460 bypass – the main road leading to Virginia Tech:

I am somehow reminded of Sideshow Bob from The Simpsons…

Two hedge rows. One of green Japanese barberry (Berberis thunbergii, cultivar unknown); the other of the purple form (Berberis thunbergii var. atropurpurea) Side by side, they make their way up the median, alternating from the right-hand side of the culvert to the left, like two caterpillars in love. Ooooh, lovely! Or at least SOMEBODY thought so.

Issues: 1) Barberry is a prolific fruit-setter and has made several state’s “Invasives” list. It’s outright prohibited in Massachussettes (can’t buy, sell, or import it). In our Blue Ridge Mountains of southwestern Virginia, it is popping up with startling regularity in state forests, road sides, open fields, etc. Interestingly, most of what I’ve seen is the purple form. 2) It’s very thorny. Which means most of the time it is adorned with plastic bags and other perforatable garbage. 3) They are actually mulching, pruning, and weeding this mess, which stretches for at least 2 miles. Best use of state budget/manpower??

I realize purple Japanese barberry is one of the bread-and-butter staples of many nurseries and garden designers. Folks just love the deep reddish-purple foliage. Virginia Tech’s school colors are maroon and orange, so this is the go-to shrub for campus landscapers and ardent alumni desiring that particular color scheme (see below for our “living VT”). Very fun! Growing next to a trillium on our section of the Appalachian Trail? Not so much.

Approximately one gazillion people get their photo made next to the VT logo each year – pretty good public relations for a noxious weed.

No Way! Something that actually works?

Sometimes I feel guilty because I always seem to be putting down the products that people sell to make their living. But not today! Today I’ve got something that actually works! No, it isn’t pretty, and it does have some irritating problems, but I can honestly say that it does what the company that manufactures it says it does. And that product is the Aqua Globe.

This is a very simple contraption (which is part of the reason that it works). It’s just a glass ball with a hollow tube connecting to it. At the base of the tube there’s a hole where water can be poured it to fill the globe. When you push this into a container it will release the water in the globe slowly and give an extra day or two between waterings. This contraption doesn’t affect the drainage of the media that you put it into, and it works with most types of media.

The down side to this thing is that….well….it’s kind of nasty looking. The other problem with it is that, after you push it into the potting soil, it’s hollow tip will fill up with media, so when you fill it with water the next time you need to dig that media out with a fine-bladed knife or a thick piece of wire. But hey, if you’re going on a short vacation and you’re feuding with your neighbors, then this little contraption will do the trick.

Modern day torture stakes

Torture stakes were used centuries ago as a slow means of executing prisoners. Unfortunately, the practice lives on every time someone incorrectly stakes a newly planted tree. Though I’ve written about tree staking before (click here to read more), I’ll use today’s blog to demonstrate another unintended result of improper staking – decapitation. A normal tree develops taper as it grows. At eye level, a tree trunk is narrower than it is at ground level: that’s taper. As the trunk flares out and morphs into roots (Figure 1), a buttressing structure is created that allows trees to remain upright, even under windy conditions.

Figure 1. Trunk flares as it meets soil and roots begin.

A tree that’s been staked too high, too tightly, and/or for too long does not have this structural protection. Instead, the staking material creates an unnatural pivot point, which is not structurally capable of withstanding wind. When the inevitable windy day comes along, the trunk snaps at this point (Figures 2-3):

Figures 2 and 3. Tree decapitation, up close and personal.

Unlike the victims of the original torture stakes, trees don’t necessarily die after breakage. They are, however, permanently deformed and have little aesthetic value. If trees need to be staked at planting (and many times they do not), staking needs to be low and loose to allow taper to develop normally. (More information on proper tree planting can be found by clicking here.)

Fabulous Sporobolus!

“Where have you been all my life?!!”

Every once and a while, I come across a plant and simply fall in love.

I am not alone on this particular species, and the bandwagon is getting mighty crowded. Sporobolus heterolepis is the object of my affections…it even has an intriguing common name – Prairie Dropseed. It’s native to much of North America, short of the West Coast. Though most widespread in the Midwest, there are isolated populations in Virginia, North Carolina, and Pennsylvania. It’s even hardy up in the Arctic North (where Jeff and Linda live).

Sporobolus shows off some fluffitude while Echinacea tennesseensis look on in amazement. Author’s garden.

Now on to the juicy description: fine, green foliage forms fluffy mounds or tussocks up to one and a half feet tall and up to two feet wide. I describe it to my students as “pet-able” – one just wants to run their fingers through the flowing locks… The tiny, fragrant flowers appear in late summer form a fluffy cloud above the foliage and wave about on slender stems, even with the slightest breeze. I think the flowers have a coriander scent, have also heard buttered popcorn and vanilla. Seeds form and then drop to the ground around the plant (hence the common name), at which point the birds scarf them up. There is very little actual germination; the species is in fact endangered or threatened in several states (USDA Plants Database). As the weather cools, the fall color can range from bronze to orange to apricot – just gorgeous – and then turns to a tawny buff for the remainder of the winter.

Newly-planted in the Hahn Horticulture Garden at Viginia Tech – check out that fabulous fall color!

As with many prairie natives, this a very tough character once established – puts up with lousy soil, little rainfall, and is definitely drought-tolerant. We’ve added more than 100 of them to our campus meadow garden. At my favorite public garden, Chanticleer (Wayne, PA), they’re planted in huge drifts and are managed in the “natural” way, with controlled burns in the early spring.

Doubt you’d find it at a big box store, but it should be available at an independent garden center near you! Please note this one of those species that does NOT look very exciting in the pot, especially in the spring (green, grassy, that’s it). But give it a season or two in your garden and…[cue romantic violins…].

Global Warming, Carbon Dioxide, and Plants

There was an article published recently that traced the melting of glaciers in the US over the last 50 years. This study showed, pretty convincingly, that the glaciers are, indeed, melting, and melting rapidly. Meanwhile, in our atmosphere, levels of carbon dioxide from humans burning fossil fuel are increasing in a manner roughly correlated to the increase in temperature that’s melting the glaciers. But is the carbon dioxide actually causing the warming? Believe it or not this is still an area of discussion among scientist, and the answer isn’t as simple as many newspapers make it out to be. Almost all of the scientists that you care to talk to, even those skeptical of the role of carbon dioxide in global warming, admit that increasing carbon dioxide is going to cause a net increase in global temperature. But there is a decent amount of research out there showing that solar and geothermal activity (in other words things that we can’t control) may cause anywhere from 15 to 75% of the warming that we’re seeing. To be honest, based on what I’ve read (and I’m no climate scientist), I tend to side with those who believe that global warming is mostly caused by human releases of carbon dioxide, but I also think that to accept that theory as proven is a mistake.

In my humble opinion we’re missing the more compelling reason to reduce our emissions of carbon dioxide (besides the fact that we’re running out of fossil fuels of course). Plants. Most people simply assume that, temperature increases aside, increasing carbon dioxide in the atmosphere is going to be good for plants, and that’s just not the case. True, some plants, like Canadian thistle and many other weeds, love the increase in carbon dioxide, but other plants, such as many grasses, just don’t respond to it that well. The ironic thing is that, for those plants that respond strongly to CO₂, nutrients like nitrogen and potassium are taken up quickly from the soil (as you’d expect with a rapidly growing plant) and then, as the nutrients in the soil run out, the growth of the plant is drastically reduced. In other words, CO₂ causes unfertilized soils to become more rapidly depleted. So what does this all mean? It means that as we increase CO₂ levels in the atmosphere we’re changing the world’s ecosystem, including the fields that grow our crops. Indeed, we’re actually adjusting the atmosphere to alter which plants are most appropriate for certain situations. There are even those who argue that, because of our CO₂ emissions, we’re encouraging invasive plants to take over our native forests because these plants tend to be able to handle high CO₂ (and high temperatures) better than the plants that are already there.

To me this is the more important reason to reduce our carbon footprint.

The other side of nurseries

As some of you know, my background is somewhat different from most faculty members in Horticulture in that my roots (no pun intended) are deepest in forestry. I’m sometimes asked to compare and contrast various aspects of horticulture and forestry. There are certainly differences – some of which I’ll get into in later posts – but there are also a lot of similarities. One of the truisms that seems to pervade both fields goes something like this: “When all else fails, blame the nursery”. Whenever a tree dies, whether it’s a 2-0 bare-root seedling or a tree that was spaded in with 60” tree space, the first reactions is “Must’ve been bad nursery stock”. Um, could it have been that the tree planting crew left the bundle of seedlings in the 90 degree sun all afternoon or that 5” caliper red oak really doesn’t belong in a bathtub? I bring this up because often we see suspicion, if not downright hostility, aimed at landscape nurseries. I thought of this as I was touring J. Frank Schmidt and Sons nursery this week near Boring, Oregon (yes, there really is town called Boring). J. Frank Schmidt and Sons is one of the largest wholesale producers of shade trees in the country. If you walk into virtually any garden in the northern half of the US, chances are you will see trees that began their life in the Schmidt’s fields under the shadow of Mt. Hood. J. Frank Schmidt nursery is among the most progressive nurseries in the industry, investing in new plant development, in-house research, and supporting university research through the J. Frank Schmidt Family Foundation and donating thousands of trees for research trials. During the tour, our host. Jim Ord, was excited to show us an air-slit container that Schmidt had developed for to reduce circling roots in container-grown trees. As I mentioned at the outset, we are often quick to blame nurseries for causing problems, here’s an example of a nursery working to solve problems. And this is just one example, Schmidt and other nurseries are working to develop and promote new elms and other species to provide a wider array of trees to replace ash trees in the wake of the Emerald Ash Borer. In some ways Schmidt is unique due its size and progressive stance but other ways it is very similar to a large majority of wholesale nurseries which with I interact. While there are certainly issues that trace their roots to problems in nursery production, most nurseries take great pride in their products and work constantly to refine and improve their growing techniques.

What’s in YOUR soil? (with apologies to Capitol One)

Urban environments are always challenging for landscape plants just because they are anything but “natural.” Temperatures are higher, water is often less available, and compacted soils have all the nourishing qualities of concrete. The single most important thing you can do to ensure long-term success of landscape trees and shrubs is to get their roots well established in the soil.

I’m going to leave the topic of soil amendments to another day (but you can find my myth columns about them at http://www.theinformedgardener.com under “Horticultural Myths”). What I want to focus on is our propensity for fertilizing landscape trees and shrubs without really knowing why, or when, or if we should be adding any particular plant nutrient.

The smartest $13 you can spend is to have a soil analysis done before you add anything to your soil. My favorite soil testing lab is the University of Massachusetts at Amherst. That $13 will buy you a complete standard analysis of the available nutrients in the soil, plus a measurement of the soil’s organic matter content. Of course, there are many other soil testing labs you can use, but UM’s Amherst lab is only providing you with information – not a sales pitch for amendments and fertilizers.

Why is this so important? Let’s say you go to a nutritional supplement store, buy every possible supplement, and take them all. Do you need all of these? Probably not. It would be smarter to talk to your doctor and find out what you’re missing, right? It’s the same with your soils. Don’t assume your soil needs a lot of phosphorus, even though transplant fertilizers are loaded with this element. Non-agricultural soils often contain abundant levels of this nutrient, and too much phosphorus will hurt mycorrhizae and contribute to water pollution. Take a look at this portion of a soil test for an organic demonstration garden:

Figure 1. Note the high level of organic material in this soil, which contributes to the nutrient overload.

The trick to fertilizing landscape soils is understanding that landscape soils are not agricultural soils. You’re not harvesting crops (an activity that depletes the soil of its plant nutrients). Urban landscape soils usually have high enough levels of most nutrients to sustain plant growth. But you’ll never know unless you have your soils tested.