Harvesting an Experiment

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This has been an exciting week for me.  On Monday we started cleaning off 72 rootballs of various tree species that had been planted 5 years ago for a study.  These trees had been planted in containers and become potbound at the nursery from which we received them.  We treated them in one of three ways.  Either we did nothing (in other words we just dropped the pot bound tree in a hole), we used the standard methods that Universities recommend for slicing potbound roots (Four deep slits down the sides and a deeply cut X across the bottom), or we cut off all of the circling roots by cutting the pot bound root system into a box shape.

A root ball cut into a box shape

The plan was to harvest after 4 years to see what happened – we decided to wait 5 – and boy did we see some interesting stuff.  At this point our results are preliminary – we need to run statistics before we can say anything conclusively – but this is what my eyes tell me.

  1. Trees that had their roots cut into boxes suffered reduced growth the first few years, BUT, their root systems look as good as any root systems that I’ve seen – almost no circling.
  2. We planted our trees with the surface of the soil at the same level as the surface of the media in the containers – which is too deep in most cases.  For trees with circling roots this created a severe problem as the circling roots often surrounded the stem – potentially causing suffocation of the tree later in life.
  3. Root systems that were cut using the 4 slit method didn’t look much different from those that weren’t cut at all.
  4. The number of large roots emanating from all of the treatments appeared to be about the same (we’ll need to run the stats before I commit to this one).  This is particularly interesting because many people expect large roots that are circling to continue circling — but that isn’t what usually happens (unless the hole where the tree is planted has hard sides which can force the roots to circle just like the container did).


This root system was from a control — no root pruning at all, but still plenty of large roots.

No matter what the results/statistics end up saying there will be more questions.  For example, all else being equal, how damaging are circling roots to the health of a tree if the tree is planted properly (no stem tissue under the surface of the soil) and the circling roots are under the surface of the soil?  If the answer is that circling roots under the surface of the soil aren’t very damaging (after all, there’s no stem tissue for them to crush) then why are we bothering to try to root-prune pot bound plants at all – what we should really be concentrating on is planting at the proper depth.

All the above is hypothetical though – I just enjoy thinking about this stuff as the data starts to roll in.  As we get more definitive answers and start to run the statistics I’ll let you know more.

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Pause for effect…

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Spring (in either hemisphere) is an incredibly busy time for anyone even remotely associated
with horticulture – a frenzy of growing, selling, buying, planting, and
information-disbursing.  If gardening were this wildly popular year-round, there might even be some money to be made. For us Hort faculty,  spring means field trips,  student plant sales, cramming even more plants
onto an identification test (heh), tons of consumer questions, research projects coming and going, and many many speaking engagements. As gardeners, we’re also trying to get all that stuff done, too – weeding, mulching, planting recent purchases or gifts from plant-sharing friends (the best kind). It’s hard to slow down and enjoy spring.  Joel and I did a “forced pause” last evening before dusk. We put down the implements, poured some white wine, and simply wandered around our garden.  So many things coming up and out; it was breathtakingly lovely, all the fresh foliage and flowers, basking in the last of the day’s sunshine. Please don’t let spring rip past without stopping to sniff the
Convallaria. Unless it’s still under snow (sorry Bert!).

My favorite little Japanese Maple – Acer palmatum ‘Tsuma gaki’. Looks like she just got her nails done.

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Mortal Kombat – garden version

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Soil solarization is regarded as an environmentally friendly alternative to pesticides for controlling nematodes, weeds and disease.  Sheets of plastic (generally clear) are spread over the ground and solar energy heats the soil underneath to temperatures as high as 55C (or 131F).  Since the soil environment is usually insulated from temperature extremes, the organisms that live there are unlikely to be resistant to heat stress.

This is a practice best suited to agricultural production, where monocultures of plants have attracted their specific diseases and pests.  Decades of research have shown success in controlling pests in greenhouses, nurseries, and fields.  But there’s a down side to this chemical-free means of pest control.

It shouldn’t be surprising that beneficial soil organisms, in addition to pests and pathogens, are killed by solarization.  Studies have found that soil solarization wipes out native mycorrhizal fungi and nitrogen-fixing bacteria.  One expects that other beneficial microbes, predacious insects, and parasitoids living in the soil (but so far unstudied) would be eliminated as well.

This may be an acceptable loss to those who are producing crops; soil can be reinoculated with mycorrhizal fungi, for example.  But for those of us caring for our own gardens and landscapes, this is literally overkill.  (And consider that most of us probably have trees and shrubs whose fine roots extend over our entire property.)

So this spring, instead of solarizing your soil, consider some less drastic measures of pest and disease control. Minimize soil disruption to preserve populations of desirable microbes. Plant polycultures (more than one species) in your vegetable garden, or at least practice crop rotation.  Protect and nourish vegetable gardens with compost.  Use coarse organic mulches, which provide habitat for beneficial insects and spiders, in landscaped areas.  Above all, try to treat your soil as the living ecosystem it is, rather than a war zone.

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Guest inquisitor reveals all

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The odd oak in Friday’s photos is shin oak, or Quercus sinuata var. breviloba:

 

This trunk “puddle” is a really cool adaptation called a lignotuber (good job Matilija!) or burl.  These are common in woody plants found in wildfire zones.  New sprouts can arise after fires have roared through, or perhaps after heavy browsing by deer, as the park ranger suggested to Ginny, our guest inquisitor.

Thanks, Ginny, for sharing the photos and question.  If you have an interesting plant quiz topic, preferrably with pictures, feel free to pass it on for our Friday Question!

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Friday quiz – guest inquisitor!

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Reader Ginny Stibolt passed this one on to mull over the weekend:

“We stayed at the Llano River State Park in Texas where I spotted this weird growth pattern of a gnarly oak–it’s like a puddle of trunk from which the main trunk arises. The camp host, who seemed to be well informed, said that these were Spanish oaks in the white oak division and that a root disease causes the expansion of the base of the trees. About 1/4 of them, here in the camping area, have this malady and often new sprouts grow from the wide base. Spanish oak does not seem to be the “correct” common name, and in looking at the native oaks for Texas, I couldn’t readily identify it. So a mystery or two…”

 

So what kind of oak is this, and why does it have this weird trunk base?

Ginny has an update, and I’ll post it on Monday.

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Invasive plants, politics and science

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I’ve had a hectic week (taxes! financial aid!) and haven’t had a chance to think about posting.  Fortunately, yet another colleague just sent me an interesting link that’s worth sharing and discussing.

For those of you who aren’t familiar with how Master Gardener programs work, they are built on volunteers who receive training in garden-related sciences and then contribute a significant number of hours to outreach education.  Many MGs work in plant clinics, and others volunteer in public gardens.  Regardless of where they spend their volunteer hours, they are always representing their sponsoring university and therefore dispense advice and follow practices based on the best available science.

This will help explain why the Master Gardeners who volunteered at the Racine Zoo felt they had to resign their volunteer positions.

(Note that the zoo is losing out on 1300+ hours/year of donated garden upkeep, but the zoo president and CEO is confident that the zoo staff can pick that up.  Wonder if he’ll be out there weeding and watering?)

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Why did the worm cross the road?

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…To get to the other side. Of course.

All the rain we’re having is causing the earthworms to crowd the sidewalks and driveways. They fling themselves out of the ground and onto the pavement because they’re drowning, right?  Nope. Urban myth (by the way, why are there no Rural Myths?).  The punchline is not too far off: they can only move about above ground while it’s raining. They use rain events to safely relocate, and can allegedly live for a while in a puddle.  But we all know what happens when the sun comes out…crispy Ramen time.

I had just come in from flinging a bunch of worms off the pavement in front of our building – they were going to get mashed or eaten by robins otherwise. I probably put them right back from whence they came, against their earthwormy wishes.

 
Portrait of Two Worms
– by H.L. Scoggins


Then I read Bert’s post…it’s like reporting that the Easter Bunny has rabies or something. I’ve always been delighted to see earthworms, under any conditions. To the point of saving their squirmy little lives whenever possible. Not sure what to think about this new bit of information.

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Invasion of the killer earthworms

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It sounds like a B-grade horror movie.  Millions of earthworms, moving silently beneath soil, wreaking havoc until the entire planet is uninhabitable.  Sound a little far-fetched?  Not to ecologists that study northern hardwood forests.  While most of us grew up thinking earthworms were ubiquitous, turns out they are not native in parts of North America that were covered with ice during the last glacial period.  Most of us also grew up thinking that earthworms where the good guys/girls (they’re hermaphroditic), churning up compacted soil and leaving nutrient-rich castings behind.  In many northern hardwood forests, however, exotic earthworms, have become invasive and ecologists believe they are having profound effect on ecosystems.

I have to admit I hadn’t paid that much attention to the invasive earthworm issue but I attended a seminar last week by Dr. Lee Frelich, Director of the Center for Forest Ecology at the University of Minnesota.  Dr. Frelich’s seminar touched on several areas of research, almost all of it extremely depressing, related to climate change and invasive species.  He and his colleagues have documented significant changes in soil ecosystem processes and plant succession associated with increasing populations of earthworms.  Nightcrawlers, in particular, cause a lot of problems because they consume fresh leaf litter causing it to decompose at a much faster rate compared to un-invaded ecosystems.  The net result of these soil changes is that few trees or shrubs can reproduce in the understory.  Over time this may lead to a very different looking forest than exists there today.

Of course, we may end up with a very different forest in any event, given some of the climate change scenarios Dr. Frelich presented.  One worst-case model predicted the climate of the Boundary Waters area of Minnesota would resemble that of present-day Oklahoma City by the end of the century.  But I try not to worry; I figure by that point I’ll be food for the earthworms anyway.

 

 

For more info on the earthworms that ate Minnesota, check out these links, if you dare…

http://www.scientificamerican.com/article.cfm?id=invasive-earthworms-denude-forests

http://www.dnr.state.mn.us/invasives/terrestrialanimals/earthworms/index.html

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