Garden Myths Busted: Harpin, Top Pruning, Sanitizing Pruners, Foliar Feeding
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Garden Myths Busted: Harpin, Top Pruning, Sanitizing Pruners, Foliar Feeding

By Paul Rodman (paulgrow)September 5, 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.

Gardening picture

My intention when I began to write the Myth series was to encourage dialog and discussion on various gardening subjects. My articles are based on scientific evidence by 2 reputable horticulturists and educators. Linda Chalker-Scott Ph.D. and Jeff Gillman Ph.D. tested and researched the various topics in university laboratories.

Since becoming a Master Gardener many years ago I have always tried to make decisions regarding my yard and garden based on proven scientific theories and findings.
I believe that the first topic will indeed create a lot of dialog and opinions.


The Myth
Harpin will encourage plant growth and discourage disease.

The Facts
Yardeners are always looking for ways to reduce the use of harmful chemicals in the garden whether it is fertilizers, pesticides, or herbicides.
Several years ago a company called Eden Bioscience came out with a new product that was touted to be the "magic bullet" to encourage plant growth, insect and disease resistance. The product was harpin, which was marketed under the name "Messenger".

I too along with many other gardeners hungry for new products "drank the Kool-Aid" and jumped on the bandwagon. In fact my first purchase of this product was at a group purchase here on Davesgarden.com  I used it for a couple of seasons and was unimpressed mainly at the rather high price vs. the perceived results. I saw some improvement in my tomatoes but didn't think the high price warranted further purchases.


Dr. Chalker-Scotts was initially impressed that the new product carried the Environmental Protection Agency bestowed its Presidential Green Chemistry Challenge award on Messenger. However upon contacting the EPA Dr. Chalker- Scott discovered that their efficacy data was reported by the manufacture and not any impartial third party. Sound familiar, perhaps like the FDA issuing permits for new drugs?

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Here are some direct quotes from the manufactures sales literature:

  • "A vaccination that naturally supercharges every plant in your garden".
  • "Messenger treated plants are healthier, more vigorous, and better able to resist stress".

Reports from Cornell University, Iowa State, Kansas State, and Michigan State University , Texas A&M,  and University of Tennessee did not show any more resistance, or better performance than plants without the application of Harpin.

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However Davesgarden.com member Dr. Carolyn Male, whose opinion I value greatly, recently posted here on DG. Carolyn has used the product and seems to have had good luck with it. You can read her post here.

Conclusion:

  • Experiments in the lab do not always translate into success in the garden.
  • Consider the cost factor and practical drawbacks to any new product.
  • Do your homework before putting any new on your plants
  • Don't succumb to advertising hype.


Eden Bioscience has sold out and Harpin is being marketed under a variety of names such as AXIOM. It is being packaged a little differently so the price has been reduced somewhat.

Only you can be the judge as to whether or not you want to use it in YOUR garden.

 

The Myth
When pruning diseased plants, trees or shrubs you show disinfect your pruners with bleach to prevent spreading disease.
 

The Facts
If you are like me we all have our favorite pruners, lopers, and pruning saws. Those of us serious gardeners spend substantial sums of money on quality pruning tools. I've had my Felcos for over 10 years and unless I lose them will probably be the only pruners that I'll ever own. It's very important whether you have top end or moderately priced tools to maintain them correctly.

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I would venture to bet than the majority of websites or books that you might check for pruning diseased plants might read something like. "When pruning diseased plants disinfect your pruners with a 10% bleach solution after each cut.


WRONG!!!

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Chlorine bleach causes pitting; bleach is an oxidizing agent which means that it is corrosive. There is also a health hazard to humans when exposed to chlorine especially those with respiratory problems.
There is also a danger to plants when exposed to chlorine bleach.  Bleach is extremely phototoxic to plants. Any bleach left on your pruners will damage the next plant cell it touches.


What to use.

There are several choices that are not harmful to plants that will kill any disease that might be on your pruners and not damage your tools.


Rubbing alcohol is safe and relatively inexpensive.

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Listerine is another good choice. If it can be used in your mouth it won't hurt your plants.


The preferred disinfectant is LYSOL the old household standby. It won't harm your pruners and will kill any bad germs.

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One final note, NEVER apply any disinfectant any fresh cut on a tree or shrub.

The Myth
When transplanting a tree or shrub you should prune the crown and lateral branches. The thinking behind this is if you reduce the biomass above ground you need to compensate for the loss of some roots that are lost during the transplanting process.

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The Facts

Many books and web sites suggest  to prune the crown and lateral branches as much as 50%.  The theory is that this will reduce transpiration, and compensate for lost or damaged roots. (A rule of thumb when pruning, never remove more than 30% of a plants branches in one year)

In fact many .edu sites offer this same suggestion. The problem is their advice is supposed to refer to containerized plants and is directed at the nursery industry. This helps to reduce shipping costs. This is not intended for plants in the landscape. Studies done on landscape plants have shown that pruning when transplanting is not beneficial and may actually harm the plant.

When growing tips are removed from most plants the plant responds by sending out lateral shoots below the cuts.  This results in a bushier plant; this in turn can destroy the natural form of a tree or shrub. Have you ever noticed a blue spruce that has had the top or terminal buds removed? It sends out side shoots that creates a shrub that doesn't resemble a blue spruce at all.

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Trees and shrubs left intact after transplanting may appear to me dormant to an untrained eye. In fact they are putting all of their energy into root growth. When the roots have reestablished bud growth will resume.

There is no need for pruning when transplanting. Only branches that have been damaged during the move should be pruned, nothing else.

 

The Myth
Fertilizers sprayed on the leaves of trees and shrubs are more effective than soil applications.

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The Facts

Foliar feeding involves spraying the foliage of plants with water-based fertilizers. The logic for the practice is based on scientific research from the 1950's, which demonstrated that leaves can take up minerals  This research is consistently cited in the argument that foliar feeding is 8, 10, or even 20 times more effective than traditional soil application.

The original 1950s research came from Michigan State University and was particularly useful in understanding how nutrients move within plant tissues.

Obviously, materials applied directly to a leaf are more likely to enter the leaf in large quantity than the same materials applied to the soil.

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Research over many decades has explored the mineral uptake and transport of many species of fruit trees, conifers including pine and spruce species, and some hardwoods. Results have been mixed in many cases, with some species responding well to treatment and others remaining unaffected. Generally, the results suggest that foliar application of particular nutrients can be useful in crop production situations where soil conditions limit nutrient availability.

The existing research does not justify foliar application of landscape plants as a general method of fertilization. It can be useful for diagnosing deficiencies; for instance, spraying leaves with iron chelate can help determine if chlorosis is from iron deficiency. It would obviously have benefit for those growers with landscape fruit trees that perpetually have flower or fruit problems.
 

Applying fertilizers to leaves (or the soil) without regard to actual mineral needs wastes time and money, can injure plant roots and soil organisms, and contributes to the increasing problem of environmental pollution.


DON'T GUESS GET A SOIL TEST!

There you have it; another installment of Garden Myths. Some of you will agree and some of you will disagree and not put any credence in the findings. The important thing is to take the time and discuss the facts with your fellow gardeners.


  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
Foliar feeding for fruit trees Nejacobs 0 5 Sep 16, 2012 4:50 AM
Now I can chuck that Messenger sample wandygirl 0 4 Sep 13, 2012 7:15 PM
good words here trackinsand 2 44 Sep 12, 2012 8:02 AM
Foliar Feeding ElementalDomain 1 33 Sep 10, 2012 5:23 PM
Another great report! jazzy1okc 0 17 Sep 10, 2012 5:14 AM
straight talk is refreshing Liquidambar2 0 28 Sep 5, 2012 6:19 AM
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