What About the Trees – Page 11 – 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.

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.)

Evaluating ‘Scientific’ Claims

Whenever I give talks to landscapers or gardening groups some of the most common questions that come up deal with various products promoted to provide ‘miracle’ results in the garden. These are usually various soil amendments; fertilizer additives, bio-stimulants, mycorrhizae, and the like. My initial reaction to these inquiries is, “What does your current basic plant maintenance look like?” Are you mulching? Irrigating when needed? Fertilizing if needed? Pruning properly? Have you matched the tree to the site conditions?

As a culture we seem oblivious to the tried and true and gravitate to the quick fix. Look at late-night infomercials for weight loss products. Hoards of people are willing to shell out $39.95 (plus shipping and handling) for a bottle of pills guaranteed to miraculously ‘melt away pounds’. Apparently “Eat less and exercise more” is a tougher sell. For garden products claiming to produce bigger, better plants there is sometimes a grain of scientific rationale and for a few, such as mycorrhizae, there are specific situations where they can be a benefit. Nevertheless the basic rule of caveat emptor is the best guide. Remember, just about anyone can get on PowerPoint and develop some slick looking 3-D bar charts and put together a glossy brochure or cool-looking website. Here are some things to consider when evaluating ‘scientific’ claims.

English 101

Words such as more, greater, bigger, faster are comparatives. They compare one thing to another. They need to be followed by a ‘than something’. Without an object they are meaningless. Advertisers use this all the time: “New Shill gasoline gives your car more power!” More power than what? Not putting any gas in your car at all? So what does a claim that a stimulant produces ‘more and stronger blossoms’ really mean?

What’s compared to what?

Some manufacturers go further and compare their product to an untreated control. This is a step in the right direction but can still be somewhat misleading. A common example is various bio-stimulant products, which often contain various enzymes and nutrient elements. Compared to an untreated control these may indeed improve plant growth. But is this due to a unique and patented blend of dung beetle excrement and papaya extract or simply the fact that a product contains essential plant nutrients? A better comparison would be to compare plants receiving the miracle product and plants receiving a conventional (and less expensive) fertilizer containing similar nutrient elements.

The bottom line, as always, is if something sounds too good to be true, it probably is. Before reaching for an exotic concoction of eye of newt and wing of bat, consider the basics of site selection and landscape plant management. Chances are there is a lot more to be gained from mundane matters such as putting the right tree in the right place than from trying to remedy the situation by sprinkling some magic dust over the roots.

Mulch Volcanoes

After Linda’s post yesterday I just had to add my own 2 cents about gator bags. I use ’em and I like ’em. But, that said, I never allow gator bags to sit against trees for an extended period of time (Maybe 6 weeks when the tree first goes in). That’s just asking for trouble! But looking at those bags got me thinking about a project which we’re finishing up this year. Volcano mulching. Believe me, it sounds a lot cooler than it is. Volcano mulching is when you make a big pile of mulch along a tree’s trunk, as in the picture below.

The reason we’re looking at volcano mulching is that everyone says it’s bad, but no-one has really proven that it’s bad. The reasons that volcano mulching are supposed to be bad are twofold: First, the mulch could cause rot on the tree’s stem (as with those gator bags) and second, because it might be possible for a tree’s roots to grow up into the mulch, potentially surrounding the stem, which might lead to the roots choking the stem as the tree grows larger. Not a good situation. Anyway, early in 2007 we took a field of maples and cut squares in their trunks, as seen below, and then either did or didn’t mound up mulch around these tree’s stems.

What we expected to see was that, over time, the wounding and presence of a mulch volcano would lead to diseases in the stem. Instead what we found is that, for many of the trees, deeper mulch actually led to the wounds closing more rapidly. The image below is of a wound that was covered with mulch.

While this next image is of a wound that wasn’t covered with mulch.

Of course some of the wounds without mulch closed fine as well, as you can see in the next image. (Why isn’t anything ever cut and dried?)

So what does all this mean? Well, nothing yet. Research is a funny thing: it rarely gives you quick and easy answers. I won’t recommend mulch volcanoes because we still haven’t examined those roots that may enter the mulch and surround the stem. And before I say that the volcanoes didn’t affect stem rot in this study I want to take a closer look at those wounds by cross sectioning the tree which we’ll probably do this fall. Plus we’ve got to run statistics on all the different trees….. and then it would be great if someone else would take a stab at this study to confirm what we see…. I tell you what, nothing’s easy.

Long term problems with Tree Gators?

So, Bert, you (and others) have done research on Tree Gator-type products and found them useful in providing water to newly planted trees and shrubs. For those of you that haven’t seen supplemental irrigation products, they are heavy-duty plastic bags that zip up to create a sleeve around tree trunks and drip water from their perforated bottoms (Figure 1). The City of Seattle uses them routinely, but I’ve seen a number of trees fail in spite of the additional irrigation. While many of these failures are undoubtedly the result of poor root systems, inadequate root preparation, and/or improper installation (Figure 2), what worries me is the long-term effect of these sleeves on tree trunks. I’ve seen nothing in the scientific or professional literature about this possible problem. So I thought I’d do an informal assessment of Tree-Gatored trees. Given what I’ve found, though, I’m tempted to do a more structured survey.

Figure 1. Tree Gator Figure 2. Poorly planted tree

First, I found a number of Tree Gators that were empty – probably close to half were nearly or completely drained. These devices don’t too much good if they aren’t kept filled. That’s an easy problem to fix compared to what I found when I unzipped the bags to look at the tree trunks. When the bags are full, they press against the trunk, creating a humid, dark environment (Figure 3) that’s only made worse when rainwater seeps into the space. As you can see in Figure 4, over time the bark rots, allowing insects and disease into the living tissues. The insects ran when I opened the bags, but I saw numerous pillbugs and millipedes – which feed on decaying matter – in those trees with rotting trunks.

Figure 3. Unzipped Tree Gator         Figure 4. Rotted bark
(note wet bark on lower trunk)        (note millipede on left side)

I think there can be fatal problems for young trees when these bags are used long-term. IMO, supplemental irrigators that resemble rubber donuts laid over the root zone are better designed. I would be sure to have a mulch layer protecting the soil from compaction by these water-filled rings, but at least the trunks are left uncovered.