Author: Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and a Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - www.facebook.com/TheGardenProfessors "The Garden Professors" Facebook group - www.facebook.com/groups/GardenProfessors Books: http://www.sustainablelandscapesandgardens.com

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…

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.

Root%20flare.jpgFigure 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):

        Decapitation%20close.jpg

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.)

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.

Bad roots and deceptive marketing

I guess today’s blog should be entitled “The Cranky Garden Professor.”   Really, I’m not always cranky, and when I am I go outside to do something constructive in my garden.  Last weekend I finally tackled a 5-gallon container of lavender that I’d bought several weeks ago.  I had intended to wait until fall to transplant it, but I was watering it every day to keep it from wilting.  I figured I might have better luck getting it into the soil where a good mulching would help keep the soil moist without daily watering.

So I carefully slid the lavender out of its pot and into my root-washing tub (Figure 1).  (If you’re not familiar with root washing trees and shrubs, be sure to check out my web page.  I’ve got a fact sheet and some myth columns on why it’s important to bare-root containerized and B&B woody plants before installing them in the landscape.  Please visit www.theinformedgardener.com to access the entire site, or this link for a fact sheet.


Figure 1.  Five little lavenders.

As I worked the potting media out of the root mass, I suddenly discovered why I was using so much water to keep the lavender happy.  It wasn’t one plant.  It was 5 separate lavender plants all placed in the container to LOOK like one large plant.  Worse, all 5 plants had some of the crummiest root systems I’ve ever seen (Figures 2-6).  They were poked into the pot like little carrots.  Most of the pot was filled with untouched potting media.

    
Figures 2-6.  The beehive is back!

What you see in these figures are root systems that look like upside down beehives.  They were obviously left in their original small pots too long and developed circling root systems.  So rather than growing outwards into the soil, they stayed in these little spirals and eventually would fuse into woody knots.   They don’t miraculously straighten out when they’re put into larger containers (or the garden).  If they did, they would have rapidly spread throughout the big container to soak up all that water I was pouring on daily.

Sigh.  Now I was cranky again.  These lavender roots were just like those I’d seen on hundreds of landscape plant failures over the last 10 years.  Since these roots were so tightly woven together there was little hope of untangling them.  So I made one vertical cut through each of the root masses (Figure 7), spread them out horizontally (Figure 8), and planted them (Figure 9).

    
Figure 7.  The cut.           Figure 8.  The spread.   Figure 9.  In the ground.

This is the worst possible time of year to transplant trees and shrubs (it’s August, after all) and I most definitely put a world of hurt on these roots.   But I will say that since I moved them I have been able to reduce irrigation, since the soil holds moisture better than the potting media.  I’ll keep track of their progress through the next 12 months.  I’m hoping they make it through this summer – if so, they stand an excellent chance of growing a decent root system over the fall and winter.

Back to the cranky part.  I really resent nurseries that deliberately bunch small shrubs together in one pot to make them look like one big plant.  It certainly cost more to buy this one pot than to buy five smaller pots.  If this isn’t deceptive marketing I don’t know what is.

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.

Introducing Linda Chalker-Scott

I’m an associate professor in the department of Horticulture and Landscape Architecture at Washington State University.  I’m also an Extension Specialist in Urban Horticulture, meaning that I have a global classroom rather than one physically located on a college campus.  I’m trained as a woody plant physiologist and I apply this knowledge to understanding how trees and shrubs function in urban environments.  This is a fancy way of saying I enjoy diagnosing landscape failures – sort of a Horticultural CSI thing.

I’m a native Washingtonian, but I spent my academic life at Oregon State University and then moved to Buffalo for my first university position.  I moved back to Seattle in 1997 and worked at University of Washington’s Center for Urban Horticulture.  In 2001 we were fire-bombed by ecoterrorists (and yes, the irony of the greenest center on campus being targeted by ecoterrorists is not lost on me) and I lost my ability to do lab work.  During this time I developed a more applied research program and in 2004 I began my Extension position with WSU.

Jeff and I have never actually met, but we’ve been chatting via internet for some time.  Apparently he manages his time better than I, since he has the ability to spearhead this blog on top of everything else he does.  I know I’m looking forward to this new venue for discussing the science behind America’s favorite outdoor activity (assuming that’s still gardening and not Ultimate Frisbee or frog licking).