What About the Trees – Page 8 – The Garden Professors™

Riding the storm out

This past weekend marked our first real bout with severe thunderstorms here in Mid-Michigan. Several lines of storms moved through the mid and southern part of the state and northern Ohio. The storms in southern Michigan and Ohio also spawned some tornadoes. Around here, storm damage was confined mainly to downed trees causing power outrages and some damage to homes and buildings.

Severe weather outbreaks provide some opportunities to observe tree failures and gain insights into how they can be prevented. Or, as Yogi Berra put it, “You can observe a lot just by watching”. I was at a little disadvantage in scouting out tree damage from out most recent storm because we were traveling over the weekend and I wasn’t able to get out and about to survey damage until Monday evening. As it turns out the area most heavily affected by the storm is also fairly affluent. Folks in these neighborhoods don’t tolerate downed trees lying around very long. Nevertheless, I did make a couple of interesting finds.

A common sight after a storm in this area is wind-throw in shallow-rooted species, such as spruce and pines. We didn’t see a lot after the current storm, which was probably due to the fact that the storm moved through quickly – most of the high winds lasted only a few minutes – and the storm was not preceded by prolonged heavy rains.

I don’t have any specific data but I have seen several cases where wind-throw was occurred on trees in which mulch was underlain with landscape fabric. Perhaps coincidence, but another strike against the stuff in my mind.

This maple provided one of the best (or worst) examples I have seen of planting too deep. The tree snapped off about 6” below ground line.

Note that there are plenty of pretty stout roots that look like structural roots near the surface, but none of these originated near the current ground line. The tree was on private property and time constraints prevented me from getting permission to do an excavation, nevertheless, it would be interesting to try to find the original root flare.

By far the most common problem in this storm, and most of our typical thunderstorms, was large limb breakage associated with narrow crotches. This occurred in a variety of species; oaks, maples, elms, pines. Narrow branch angles often form from multiple leaders, which results in weak branch attachment as included bark forms and gradually reduce the proportion of wood attaching the branch to the tree. The encouraging thing, or maybe discouraging depending on your point of view, is that this is one of the most easily preventable tree defects. Pruning double leaders or multiple leaders back to single leaders and eliminating other poor branch angles when small can easily prevent this type of breakage. For most of our garden-variety thunderstorms, eliminating narrow crotches would probably eliminate 50% or more of our tree-related storm damage.

Good to the last drop

As part of our discussion of the relative merits of fall planting, Linda mentioned an article in Arboriculture and Urban Forestry that suggests that frequent, light irrigation might be better for landscape trees then the usual recommendation of infrequent soakings. While I will withhold final judgment until I see the article (I did a scan of the last two year’s table of contents for A&UF but missed the article in question), here’s my rational for following the standard recommendation.

First, the context. In discussing landscape tree irrigation I am talking about watering trees during establishment, typically during the first year after planting and maybe the second if the tree is lucky. The goal of watering in this case is ensuring survival. The questions are whether deep soakings are more likely to encourage deeper rooting where water availability is less variable than near the surface after irrigation ceases and whether infrequent watering increases drought tolerance over more frequent irrigation.

Roots follow resources
As my Woody Plant Phys students quickly learn, we avoid the teleological ‘roots seek out water’; nevertheless, roots do proliferate where resources are available. A couple of illustrations. As a Tree Physiology Project Leader with International Paper I supervised a 25 acre hardwood fertigation trial. Trees were watered daily via drip irrigation system with emitters spaced every 3’ down a row. As part of the study we did periodic root harvests. My technicians quickly learned it was an easy job: just look for the drip emitters – every three feet there was a mop of roots right next to the drippers. The notion of roots following resources is also widely reported in the ecology literature on tree utilization of ‘patchy resources’ (e.g. Gloser et al. 2008 Tree Phys 28:37-44 ). Other factors being equal deeper watering should result in deeper rooting.

Trees habituate to frequent irrigation
Another short rotation forestry example. In eastern Washington and Oregon forestry companies Potlatch and Boise Cascade operated intensively managed ‘fiber farms’ which grew 70’ tall, 7” diameter hybrid poplars on a 7 year rotation. To maintain these growth rates, trees were irrigated daily. But there was a downside: If one day’s irrigation was missed the leaders to the trees would start to wilt. Three days without water would result in leaf drop. The daily irrigation was great for growth but it turned the trees into physiological wusses.

Periodic water stress improves drought tolerance and survival
A common adaptation for trees to tolerate drought is osmotic adjustment, which is an active accumulation of solutes that enables plant cells to maintain turgor pressure during dehydration. Plants that have acclimated to stress via osmotic adjustments and other physiological adjustments are able to survive better during prolonged drought than plants that have not been pre-conditioned. For example ponderosa pine seedlings that had been subjected to brief drought events survived a terminal dry-down two weeks longer than seedlings that had been watered 3 times a week before the final dry-down (Cregg 1994 Tree Phys. 14:883-898.

What would it take to change my mind?
Obviously some of my examples here are anecdotal (though there’s plenty of hard data on osmotic adjustment and other drought conditioning effects on trees). To recommend frequent (2 or 3 times a week), shallow irrigation I would need to see: a well designed and executed experiment that compared frequent irrigation to periodic (once every 7-10 days) applying the same amount of water weekly (0.5 to 1” per week) for the first year and then documented improved survival of the trees after irrigation had been discontinued. I’m not saying it’s not possible but it goes against my personal observations with irrigated trees in a variety of settings and relevant data with which I’m familiar.

Is Fall Really a Great Time to Plant Trees?

One of the joys of working on a university campus is that construction never seems to end. As near as I can tell there are about 3,000 orange construction barrels that permanently reside on the MSU campus that simply get shuffled from one end of campus to the other every few months. Along with all the construction comes a never ending series of new landscape projects. Driving by one of the most recent projects the other day got me to thinking about the myth of Fall planting. In numerous extension bulletins and certainly in nursery sales advertising we hear that “fall is the perfect time to plant trees”.

Photo: Dana Ellison

The recent fall planting job on our campus gave me pause to think about this. I haven’t had a chance to completely survey the carnage but I suspect about a third of the trees will need to be replaced. Obviously there are lots of things that may have gone wrong here, irrespective of when the trees were planted and one exception doesn’t prove the rule. Nevertheless when I look back on the planting disasters I’ve been called in to inspect over the years a disproportional share (I’d say by a factor of two or three to one) are fall planting jobs.

What gives? Well, the notion that fall is a great time for planting is built in a faulty premise, at least for this part of the country. Probably the most commonly cited reason for fall planting is that trees grow a lot of roots in the fall. This assumes that since there’s no shoot growth occurring, trees automatically shift reserves below-ground. There is certainly a ‘pecking order’ of carbohydrate distribution within a tree based on relatively strengths of sources and sinks. But there’s one factor that trumps all others: temperature. Soil temperature is the biggest driver of root growth. Measurements of new root growth in a cottonwood plantation in Wisconsin provide a classic example. As temperatures decline in the fall, new root growth essentially ceases. For trees that are well established, this is no problem. For trees that have just been transplanted and need to re-establish root-soil contact this is a tough row to hoe. Throw in a tough Michigan or Wisconsin winter and the tree’s facing an uphill climb.

New root growth of eastern cottonwood (top) and soil temperature (bottom). Source: Kern et al. 2004. Tree Phys. 24:651-660.

Again, most planting failures have multiple causal factors. Even if the trees on this site had been planted in the spring, they may have still experienced problems. My point is that a more accurate statement is “Fall is an OK time to plant trees”; not the ‘best’ time or even a ‘great’ time. I think these statements are often driven by the fact the fall is a slow time for nurseries and landscapers. When homeowners or landscapers ask me about fall planting the first thing I ask is if there is any reason why they can’t wait until spring, the real ‘best’ time for planting.

Killing with Kindness

With the advent of Spring comes a myriad of calls on distressed plants from homeowners, nurseries and landscapers. One of our better tree service companies (I’ll call the owner/operator ‘Mark’ to protect his clients’ identities) in southeastern Michigan called with a series of problems this spring so I decided to take drive over and get a first hand look. We looked at several problems on plants ranging from trees to ground covers but there soon emerged an consistent thread: overwatering. Plant problems related to overwatering and poor soil drainage are among the most common landscape issues I see year in and year out. The stops I made with Mark last week were typical. Mark works in several very affluent suburbs around Detroit (I know readers around the country don’t associate Detroit and affluence, given our recent press, but there is still some serious money in the area). Some of Mark’s clients spend up to $20,000 per year just to maintain the trees and shrubs on their property – that’s not including lawn maintenance. Needless to say, these folks want everything perfect. In their effort to have their landscape look more perfect than the neighbors, the homeowners and their gardeners often go overboard – especially with irrigation. One of the things that caught my attention during our site inspection was recurring issues with Norway spruce. For the most part, we regard Norways as a cast iron plant and one of the last trees with which we’d expect to have problems. Yet we saw several instances were established specimens were suffering needle die-back and declining.

In each case the trees were irrigated in situations where they would likely grow well without supplemental watering. But the trees were surrounded by ground covers or annual beds with heavy soils that were heavily irrigated. Problems usually increased on down-slope positions.

The solution? Back off the irrigation. Everyone knows trees need water, but roots their roots also need oxygen. At one site we visited, the homeowner already had his gardener running the irrigation system – in April! This is truly killing with kindness. Most established landscape trees, shrubs and perennials in this part of the world need little, if any, irrigation. Newly planted trees and shrubs need an occasional (weekly to bi-weekly) drink in the first year and some follow-up the second year. After that they can manage most years on our rainfall. In the end, a lot comes down to design. Establish thirsty annual beds where they can be irrigated without drowning hardier trees and shrubs.

Selling dawn redwood

As with last week, this past week and weekend were largely occupied by my role as a faculty advisor for the MSU Horticulture club. This weekend was our annual Spring Show and Plant Sale. Each year our undergraduates commandeer the Horticulture department’s conservatory, bring in a boatload of plants, pavers, turf and mulch and design and install a landscape. It’s actually quite a process to watch. http://www.youtube.com/watch?v=4NTPzB6YVSk
In addition to the Spring Show the Hort Club puts on a plant sale, which is the group’s principle fund-raiser for the year. My duty station for this year’s plant sale was working outside in the tree sales yard. For the record, retail is not my thing but, hey, it’s for a good cause. The star of our tree sale this year was a container-grown 14’ dawn redwood (Metasequoia glyptostraboides).

For those not familiar with this tree, dawn redwood is an incredible tree. It’s a deciduous conifer, similar in many respects to bald cypress (Taxodium distichum) but with a finer, more refined character. Metasequoia is considered by some to be a ‘Living fossil’, similar to Gingko biloba. The genus Metasequoia was originally described in 1941 from Chinese fossils from the Mesozoic era. Although local people in China knew the tree and used it as an ornamental, living trees were not formally described by botanists until 1948.

Dawn redwood is well adapted to wetter sites

Seed collected by Arnold Arboretum in the late 1940’s were distributed to universities and arboreta and this attractive, fast-growing tree found its way into the nursery trade. Ironically, millions of Metasequioa have been planted as ornamental trees but the species is considered critically endangered due to loss of its native habitat in China. Dawn redwood is extremely fast growing and some trees planted in the U.S. from the original collections in the 1940’s are reportedly 3’ in diameter.

Dawn redwoods on MSU campus

So, how did I fare in nursery sales for a day? Put it this way, I better hang on to my day job; retail is still not quite my thing – though I did move the dawn redwood and got to spend a good bit of my weekend talking about this awesome tree.

Building healthy soils?

I love living in Seattle…but I’m getting increasingly impatient with the City’s “Building Healthy Soils” propaganda. For years I’ve questioned their recommendation to perpetually amend landscape soil with organic material to no avail. Let’s see what you all think of their “fact sheet” (which you can read here in its entirety).

“The best way to improve the soil is to add plenty of compost or other organic matter throughout the entire planting area before planting. Thoroughly mixing these materials deep into the soil helps provide water, air and nutrients to plant roots.”

Hmm. No mention of how to determine IF your soil needs improving; without a soil test, you have no idea what your baseline organic matter level is.

But perhaps this recommendation is only for vegetable gardens and annual beds? Nope. In the next paragraph, we’re told to “Mix in organic material before planting lawns, perennials, trees and shrubs.” We’re given helpful how-to instructions: “Use a shovel or digging fork to mix amendments into the top 6 to 12 inches of soil. It is important to amend the entire planting bed — not just small holes for each plant. When planting individual trees and shrubs in lawns or existing beds, amend an area at least 3 feet wide, or 3 to 5 times as wide as root balls over 12 inches in diameter. Rototill large areas where digging is impractical.”

Now we’ve got a serious problem. This practice is recommended for existing beds. Not only will extensive digging or rototilling destroy any soil structure you might have, it will also take out the roots of any desirable plants in the vicinity).

But let’s continue to ignore reality and go on to the annual recommendations for adding compost to soils.
“Clay soils: 16 cu. feet (.6 cu. yard) = 2 inch layer of compost for new gardens. Use 1 inch per year in established gardens.”
“Sandy soils: 24 cu. feet (.9 cu. yard) = 3 inch layer of compost for new gardens. Use 1 – 2 inches per year in established gardens.”

Is the compost used as a mulch in these existing gardens? No – the guidelines are prefaced with this instruction: “Gardens: mix compost to 10- to 12-inch depth.” (Can’t say this does much for promoting root growth either.)

This document shows a breathtaking lack of understanding of how landscapes function, especially over the long term. It takes an agricultural practice (annual organic amendment of crop fields) and misapplies it to permanent landscapes. It is devoid of the research which continues to show that improper soil amendment can cause serious problems such as soil subsidence, perched water tables, and nutrient overloads. This last point is especially important to anyone living near aquatic ecosystems, since excess nutrients always end up in the water.

Before you plant this year, find out what your soil needs before amending it. And remember that mulching is the natural (and sustainable) way to add organic matter to the soil.

Pardon If You’ve Seen This Before…

But it still makes me smile.

First published in December 2005, it’s still up at Red Shirt Knitting. Seattle yarn artist Erika’s story is posted, as is a chronological progression of photos and events since the original “fitting”.

She actually got some pretty funny tree questions/comments about potential girdling, the possibility of damage from moisture buildup (I like her response “What are YOUR sweaters made from…neoprene?”), etc.

Tortured urban tree examples abound: poorly planted, pitifully pruned, and other horrors. I think Miss Erika should get some kind of award for this public display of [tree] affection.

Protecting existing trees – what a concept!

I just got back from a trip to Pullman where I guest lecture once a year for the Landscape Plant Management class. It’s also a chance to get some new photos for my Wall-O-Shame. Here’s my latest:

Pin oak (Quercus palustris) doesn’t drop its leaves in the winter – instead, they hang on until the following spring. So it’s really easy to see which part of this tree is alive (i.e., has last year’s leaves). It’s apparent that most of the crown has died, with only some lower scaffold branches remaining.

How did this happen? Take a look at how new that concrete is around the base of the tree (and how small the tree well is. This construction was done in 2004:

Note the complete lack of root zone protection. Not only has the majority of the tree’s fine roots been destroyed in preparation for pouring concrete, but only a very small space under the tree is “protected.” I guess the cup at the base represents the irrigation system. To top it off, this construction was done in August, when coincidentally I was there as well. It was blistering (as it usually is in the summer in eastern Washington), and the remaining leaves on this tree were wilted:

So why would anyone be surprised when, 6 years later, this tree looks like crap? And why doesn’t WSU insist on tree protection standards when construction bids are submitted?

“Being wrong” counterpoint

I haven’t finished with the water droplets story yet – but I just had to add some more evidence to the tree planting discussion from last week.

Consider this series of photos below. This is a street tree in Kennewick, WA (in the southeastern part of the state, where summers can be intensely hot and dry). Every spring, this tree leafs out just fine – and every summer the leaves suffer marginal and tip scorch. This is a classic symptom of chronic drought:

As an amenity, the tree fails. Even though the landscape is well-watered, as shown by the healthy turf in the next photo, the canopy is sparse and dry.

An excavation of the roots explains why: the tree was planted too deeply and has developed a secondary set of roots:

Note how sparse these roots are – which is typical of many adventitious root systems. While the roots are adequate for water uptake during the cool spring weather, the hot dry summers suck away more water from the leaves than this puny root system can absorb, even when well-watered.

My point: sure, trees might survive being planted too deeply. But thrive? Not in this case – and this is a well-managed landscape! With less care this tree would have died long ago. The only solution here would be to replace this tree – correctly.

Blue Spruce Blues

One of the roles I’ve evolved into over the past decade as an extension specialist at MSU is that of ‘the Conifer Guy’. Conifers are great and fascinating plants. The oldest trees in the world are conifers, the largest trees in the world are conifers, and some of the most interesting (at least to me) landscape plants are conifers. Unfortunately, for a variety of reasons, in the Upper Midwest we have gravitated to Colorado blue spruce more than just about any other conifer. Part of this over-reliance on blue spruce in the landscape is driven by production (see, Linda, I’m not always an apologist for nurseries). Growers want to grow what they know and what’s easy to grow. As a nursery tree, blue spruce is a reliable performer that is well adapted to a relatively wide range of site conditions. Of course, growers also want to grow what they can sell, and there always seems to be a steady demand for blue spruce. In many neighborhoods it appears that there is an ordinance that every other tree has to be a blue spruce. So what’s the issue? In the Great Lakes region, blue spruce often look pretty good when young. However, as trees age they become susceptible to several major pests, especially cytospora canker and gall adelgid. So all those shapely blue Christmas trees that were planted 10 or 15 years ago are now a bunch of ratty-looking messes. So what’s the solution for blue spruce burn-out? Clearly landscapers and homeowners need to think beyond blue spruce and look for a greater variety of choices. Here are three to consider.

– Serbian spruce Picea omorika Whenever I’m asked to suggest a conifer, Serbian spruce is usually one of the first trees in the conversation. While the color may not be as striking as a blue spruce, Serbian spruce still has impressive needles in its own right – bi-color with dark green on the upper side and silver below. Adding to Serbian’s charm is its graceful weeping habit.

– Swiss stone pine Pinus cembra The late, great conifer expert Chub Harper used to remark, “I never met a cembra I didn’t like.” Chub’s fondness for Swiss stone pine was well founded. Here is an understated, consistent landscape performer. Few pests, dark green needles and stately upright form.

– Korean fir Abies koreana It would be a stretch to consider Korean fir an alternative to blue spruce. While Korean fir is more broadly adapted than many of its pantywaist cousins in the genus Abies, it will still do best on the Holy Grail of moist, well-drained slightly acidic soils. Nevertheless, Korean is tougher than the average fir and is a conifer with some character and worth a shot. Korean firs are often heavy cone producers, which can add an interesting element of color.