The Latest Hort Research that Gardeners Can Use

The third is a series by the University of Minnesota's Jeff Gillman (check out his new website).  All of Jeff's research updates are available here. 

Over the past few weeks I’ve had a bunch of people e-mail me to tell me that I’m wrong about something  or another.  From the heresy I commit when I remark that applying commercially bought mycorrhizae probably isn’t going to help newly planted trees to my inexcusable audacity in commenting that commercial hydrogels haven’t worked very well in the tests I’ve conducted, it seems that some people just don’t like it when I don’t endorse their pet product.  Most point out their own experiences, some point out other research, mostly unpublished and so unattainable by me, and some just tell me I’m an idiot.  I like the last group best - they’re the most entertaining.  

 The thing that most people who voice these objections don’t understand is that I believe they should do whatever they want with their plants.  If they think that hydrogels work because their Tarot card reader told them it does, then I strongly encourage them to use hydrogels.  If they want to use mycorrhizae, then please, be my guest, use mycorrhizae.  But I’m a professor with an Extension Service appointment.  What that means is that my assignment – my job – is to transfer research-based information to those who can use it.  There’s not much more to it than that.  I take the research conducted by other researchers and myself and I make it available to the public.  If most of the research that I can find doesn’t demonstrate that something works, then I’m not going to say that it does, but that doesn’t mean that I don’t think you shouldn’t try it for yourself (with some exceptions for safety of course).

The reason for this little diatribe is that the first paper in this research update is on mycorrhizae, and it concludes, yet again, that purchasing commercial mycorrhizae is a waste of your time and money.  Now before you start e-mailing me, please note that most research shows that naturally occurring mycorrhiza are a very good thing that we want in our soil.  Unfortunately, most research also shows that commercial mycorrhizae you purchase from a store are not useful. And off we go.

NEW STUDIES   

1.  Mycorrhizae:  Our first research paper showed that applying commercially available mycorrhizae to maples and magnolias didn’t do much at all, at least not much that could be considered good. I like this quote from the paper “Commercial [mycorrhizal] inoculants are generally marketed based on the assumptions that they will increase root and shoot growth after transplant. In the present experiment, inoculation tended to decrease the former and had no effect on the latter.”  The decrease in root growth wasn't a big deal, but it certainly didn’t help. 

2. Value of Landscaping:  In an interesting survey of residents of cities in the Pacific Northwest it was established that good landscaping around a strip mall could entice consumers to pay 8.8% more for goods than they would pay in a strip mall with poor landscaping. (Did you know that the first strip mall was the Country Club Plaza in Kansas City, Missouri and was built in the 1920s? How’s that for a dubious distinction? I’m not a strip mall lover myself, except that some of my favorite restaurants are in them.)

3. Plants in Classroom:  In a who-would’ve-guessed type study, researchers in Texas established that students like it better when there are plants in the classroom and that these plants had the most effect when classrooms didn’t have windows.  It’s important that I point out that student grades didn’t increase with the addition of plants in the classroom, just the course and instructor evaluations.  Anyone want to guess how I’m decorating room 415 Alderman Hall next fall?

4. Bark Mulch with Container Plantings:  If you’re growing plants in containers you may be interested in applying pine bark mini-nuggets to control weeds.  Applying a layer of these mini-nuggets an inch thick across the top of the container controlled weeds about 90% better than if nothing was added.

5. Leaf Mulch Preventing Dandelions in Lawn:  Using chopped-up maple and oak leaves as a mulch in your lawn can be a legitimate way to help control dandelions.  In fact, in this study, conducted on Kentucky bluegrass growing in Michigan, effectiveness ranged from 50% fewer dandelions using 1 pound per square yard of leaf mulch to 80% fewer dandelions using 3 pounds of leaf mulch.

Photo credit. Study credits listed below the jump.

1. Wiseman, P. E., and C. E. Wells.  2009. Arbuscular mycorrhizal inoculation affects root development of Acer and Magnolia species. Journal of Environmental Horticulture 27(2): 70-79.

2. Wolf, K. L.,Strip malls, city trees, and community values. Arboriculture & Urban Forestry 35(1): 33-40.

3. Doxey, J. S., T. M. Waliczek, and J. M. Zajicek. 2009. The impact of interior plants in university classrooms on student course performance and on student perceptions of the course and instructor. HortScience 44(2): 384-391.

4. Cochran, D. R., C. H. Gilliam, D. J. Eakes, G. R. Wehtje, P. R. Knight, and J. Olive.  2009. Mulch depth affects weed germination. Journal of Environmental Horticulture 27(2): 85-90.

5. Kowalewski, A. R., D. D. Buhler, N. S. Lang, M. G. Nair, and J. N. Rogers, III. 2009. Mulched maple and oak leaves associated with a reduction in common dandelion populations in Established Kentucky Bluegrass. HortTechnology 19: 297-304.

Comments

[Lisa, Ontario]

Thanks for the information Jeff. I was trying to come up with some diatribe to go off on, just for fun, but I just got giggling instead. I'm glad that you just find it funny when people call you an idiot. We wouldn't want you to stop telling us all your findings!

[Michele Owens]

Jeff, the gardening world is medieval--superstitious and intolerant and willing to enrich some really bad priests--and you represent the Enlightenment.

Have you ever looked into pea innoculant? I started balking a few years ago when my Agway wanted $6 for a little package. I have noticed absolutely no difference in my pea crop without it. I'm wondering if it's only useful in soil that's been sterilized by the overuse of chemicals.

[Kathy J, Washington Gardener Magazine]

I wonder if research point 4 - isn't that ANY mulch applied is better than none as a weed block - did they compare other kinds? I think pebbles, leaf mulch, etc. would work just as well as a container top dressing. Just seems most folks don't do it, for whatever reason. I usually thrown on a handful of Leafgro just to keep in some of the soil moisture esp in my containers that sit in full blazing sun.

[Barbara]

Jeff, thanks for the info. The research on micorrhizae makes sense - local is always best.

As for plants in the classroom, I do innovation workshops and always insist on plants in the room and windows with views of greenery. Research shows that this increases creativity and idea generation. So next year not only will your students like you better, but they may be more creative to boot!

[commonweeder]

I haven't mulched my containers, but I will now - and leave enough room for the mulch. This will make the pots neater when there is heavy rain splashing mud. However I'm hoping some fine wood chips (mine are free) will work as well.

['nora]

Hey now, Michele, don't knock the Middle Ages. We could use a few more thinkers like John of Salisbury or William of Occam!

I'd characterise the mycorrhizae issue as being much more like Renaissance alchemy. Anyone got a philosopher's stone?

[Layanee]

Love your books and love this information. The gardening world is comprised of much more than Medieval and intolerant people.

Keep up the steady stream of useful information. Thanks.

[zephyr]

GELL FIGHT!!!!!!

Just kidding...

I take a pinch of "new research" (which I find most of the time to be excellent at discerning what happens on the plots of ground where the research was conducted and does not always apply to my plot of ground--except in certain cases re certain things...like the effects of "blue poison" and the efficacy of purchasing mycorrhizae)

and a dash of superstition/old wive's tales/local wisdom garnered from folks who have great gardens

cross my fingers

spit downwind

and then hope for the best.

[gardenmentor]

Thanks for the info. I'm really curious about the mycorrhizae research. Is it across-the-board or relative to specific plants/specific fungi applications? I followed some of the links above, but wasn't clear where I could find the meat of the findings -- help?

[greg draiss]

I totally appreciate Jeff's stright forward no nonsense approach. Jeff: welcome to the "idiot club" I am a member myself. I did read in a hydroponic magazine ana rticle proclaiming the benefits of mychorrizae but I do not think it works either.

The TROLL

[5998b]

He is correct, most mycorrhizal products are worthless. Check out these charts:

http://www.reforest.com/desk/questions/6676/Common+Mycorrhizal+products+tested

[Claude]

Hey Jeff,

I've just stumbled upon your site and appreciate its dedication to the localized eco-rebellion. It gives me sincere pleasure that there is somewhere out there angry about the state of gardening. I invite you over to www.pandalous.com to take part in active and thoughtful discussions on the necessity of a green thumb locale. This article might interest you: http://www.pandalous.com/nodes/gardening_for_justice

[Tara Dillard]

The Extension Service provides science based garden advice as part of their mission statement. Most resources provide garden advice while trying to sell something.

Isn't the right choice obvious?

Thanks for bringing it up.

You are the front line for scientific, new, landscape information.

Garden & Be Well, XO Tara

[Jeff Gillman]

Hi Everyone,

Michele, You make me sound so cool! I think I'm going to write "I represent the Enlightenment" as a header on my webpage! In terms of pea inoculants, I have read about them, but I haven't tried them. I would expect them to be beneficial in a location where peas or other legumes hadn't been grown before, but not in a location where they had been grown.

Kathy J -- This research was specifically on those nuggets, but yes, I'd expect almost any mulch to be beneficial.

Gardenmentor -- This research is available from the sources that I listed. Unfortunately I don't think the Journal of Environmental Horticulture is available online yet, so you'll need to get to a University library to see it.

5998b -- I received your e-mail regarding the mycorrhizae that you sell. Right now you're not much different from everyone else who tells me that their product works and everyone else's doesn't. When you have some research published in a peer reviewed journal (or at least by independent University faculty) demonstrating that your specific product works in a non-sterilized in vivo situation I will be happy to review it. Right now I consider anything that you say to be rhetoric.

Jeff

[flowers]

thanks Jeff, great information,