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Garden Myths Busted: Organic, USDA Hardiness Map, and Plant Quality vs. Cost

By Paul Rodman (paulgrowSeptember 28, 2012
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Two horticultural professionals took some of the most popular garden myths into the university laboratory to prove or disprove the accuracy of these myths. Dr. Linda Chalker-Scott from Washington State University and Dr. Jeff Gilliam from the University of Minnesota tested these myths under controlled conditions to determine if they really work.

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Myths: Produce with the USDA organic label is free from pesticides and more nutritious than produce grown in the conventional manner.

The Facts: More and more gardeners are making the decisions to grow organically. When we grow our own fruits and vegetables we know exactly what has been used as far as fertilizers and pesticides. When we buy at Farmers Markets we can ask the growers what they used to grow their produce.

When we shop at large supermarkets and see the United States Department of Agriculture (USDA) Organic label there seems to be some confusion as to what it really means. Do you think that this produce is more nutritious than fruits and vegetables grown the conventional way? Do you think that this produce is free of pesticide?

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Dr. Jeff Gillman, from the University of Minnesota takes a look at what the USDA Organic label really means. Gillman states "AS USDA ORGANIC CERTIFICATION NOW EXISTS, the USDA Certified Organic label does not provide a significant indicator that the fruit or veggies you're buying provide a significant benefit in terms of human or environmental health. Organic is a labeling term that indicates that the food or other agricultural product has been produced through approved methods that integrate cultural, biological, and mechanical practices that foster cycling of resources, promote ecological balance, and conserve biodiversity."

As far as the reason that one food has more nutrients than another has much more to do with the food itself than whether the food was grown organically or conventionally.

With regards to pesticide residue on organically grown produce, if a farmer uses spinosad, an insecticide used by organic growers, it can be present at low levels in food, as can other organic pesticides such as pyrethrum. But since residues of these organic pesticides are rarely tested you have no idea how much is in there.

The USDA organic regulation gives growers wide latitude as far as what they can or cannot use and still be certified. A study conducted at the University of Guleph indicates that some organic pesticides can have a higher environmental impact than conventional pesticides because the organic product may require larger doses. Read the entire article here.

Only you can decide if the extra cost is warranted when buying organic vs. conventionally grown produce. Just be aware that it may not be what you think it is.

Myth: The newest USDA Hardiness Map is an accurate guide as to which plants will withstand winter temperatures in your area.


The Facts:  Let's define exactly what this map is. The USDA Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. The map is based on the average annual minimum winter temperature, divided into 10-degree F zones. The most current map was released in early 2012.

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Most serious gardeners have depended on this map for years to determine which plants, perennials and shrubs were best suited for their particular area. Many of us took this information as gospel. I myself have been skeptical for a number of years as to the accuracy of this map.

Dr. Nir Krakauer is an assistant professor of civil engineering in The City College of New York's Grove School of Engineering. Krakauer conducted his own analysis of climatic data and determined that much of the country is already a half zone to one full zone warmer than the new USDA map. Why the difference? The USDA zone estimates were based on a simple average of annual minimum temperatures from the past thirty years. Dr. Krakuar's used an analysis to account for more recent warming. One of the key observations of the new analysis is that winter minimum temperatures are warming much faster than average temperatures, leading to the new hardiness zone projections.

Most gardeners experience micro-climates that may be slightly colder or warmer than the surrounding area. Plus, winter hardiness is just one piece of information in plant selection (we also need to also consider sun exposure, pest pressure, soil factors - drainage, soil pH, and so on).

So if you want to "push the zone" you can probably get away with it by going a zone warmer than shown on the map.

If you want to really track the low temperatures in your garden get yourself a min/max thermometer. This device remembers the lowest and highest temperatures that occur in your yard or garden.


Myth: The quality of plant material is directly proportional to the cost


The Facts: Linda Chalker-Scott, Ph.D. from Washington State University recently shared her findings on a couple of shopping trips to several well respected nurseries in the Seattle area to purchase shrubs and trees for her own home. The findings may surprise you.

At all of the nurseries the plants were either root-bound or had little established root growth at all. Chalker-Scott a trained horticulturist had the foresight to pull the plants from the pots to examine the root systems. This is something that we all should do when buying trees or shrubs. She also noted that some plants that were balled and burlaped (B&B) had much too small of a root ball in comparison to the crown size.

On several trees the central leaders had been pruned off to give the plant the appearance of a miniature adult specimen. Unless these trees are correctively pruned and a new leader established they will never regain their haracteristic form.

Dr. Rita Hummel, Washington State University and others has found that plant failure is usually linked to fatal root flaws. Circling, girdling, or kinked roots are problems that begin at the nursery and if uncorrected will lead to early decline and death of woody plant material.

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 Girdled roots can lead to

 a plants demise

So, when buying trees or shrubs don't think that a large price tag is the key to a perfect plant. If potted removed from the container and inspect the root mass; if root bound or girdled roots are present keep looking, examine a B&B tree or shrub and determine if the root ball is in proportion to the crown.

As usual I expect these finding to elicit a lot of dialogue. However remember these finding were reported by trained educated horticulturists.


  About Paul Rodman  
Paul RodmanPaul Rodman has been gardening for over 45 years. He is an Advanced Master Gardener, and American Rose Society Consulting Rosarian. He is President Emertius of the Western Wayne County Master Gardener Association in Wayne County, Michigan. He currently serves as the greenhouse chairman of this group. Rodman has amassed over 5500 volunteer hours in the Master Gardener program. Rodman is the garden columnist for The News Herald newspaper, in Southgate, Michigan. He has also written for the Organic Gardening.com web site. He is a certified Master Canner and has taught classes on Home Food Preserving for 7 years. He has lectured on various gardening topics throughout southeastern Michigan. His favorite pastime is teaching children about gardening. For the past several years he has conducted classes for second grade students teaching them about subjects ranging from vermi-composting to propagation.

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Discussion about this article:
SubjectTopic StarterRepliesViewsLast Post
Organic Foods greenhouse_gal 6 73 Nov 15, 2012 9:57 AM
nursery plants granitegneiss 3 56 Oct 24, 2012 12:25 PM
USDA Hardiness Map dshoemaker 3 48 Oct 1, 2012 9:23 PM
All absolutely true! ElementalDomain 0 21 Oct 1, 2012 10:14 AM
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