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Garden Myths Busted: Micro-Nutrients, Soda Pop, Salt

By Paul Rodman (paulgrowJanuary 18, 2013
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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

The Myth:
Plants should have an external source of micronutrients in order to thrive.

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The Facts:

Micronutrient mixes are commercial formulations of micronutrients that plants need but are not present in most synthetic fertilizers. These are nutrients that plants need in very small quantities such as boron, copper, manganese, and zinc. Are these really necessary in amounts besides what is found naturally in the soil?


These nutrients are usually applied via a foliar spray. Micronutrients supply elements that are needed for a plants growth but are not needed in the same quantity as the macronutrients nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. Micronutrients are applied at very low concentrations and are sometimes incorporated into regular liquid granular and slow release fertilizers in which case additional applications of micronutrients would rarely be necessary.

Sixteen elements are essential to plant growth: boron, calcium, carbon, chlorine, copper, hydrogen, iron, magnesium, manganese, molybdenum, nitrogen, oxygen, phosphorus, potassium, sulfur, and zinc. Scientists have discovered that these elements are essential for plants to grow. They found that without these elements plants will not grow and l eventually die. Micronutrients aim to prevent nutrient deficiency in your soil by offering elements that could be lacking and are not supplied by typical synthetic fertilizers.

Organic fertilizers are different from synthetics because they generally include more micronutrients and when organic fertilizers are properly used, extra micronutrients are rarely needed. Compost will also supply micronutrients to plants.


The addition of micronutrients can give your plants a boost if indeed your soil is lacking in them. This is especially true on plants grown in containers. Micronutrients usually don't get much attention due to the fact that most of our soils do indeed contain enough micronutrients to ensure healthy plant growth.

For those of us that use organic fertilizers or compost; applications of external micronutrients are usually a waste of money. I have said many times before in previous articles; I'm a huge advocate of soil testing so if there is any question as to the chemical makeup of your soil, Don't Guess, Soil Test.

The Myth:
Soda pop, syrup and other sugary compounds are good fertilizers for your plants.

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The Facts:

For years folks have been making concoctions of soda, syrup or other sugary liquids usually combined with other things such as a little dish soap and some ammonia. These concoctions are usually applied with a hose end sprayer in the area to be fertilized. Other recipes may include from 3 to 10 ounces of sugar dissolved in a gallon of water to be applied at the time of transplant. The proponents of using these sugary substances usually believe that the applications speeds the growth of good bacteria in the soil but some actually think that the sugar serves as a food or even a root stimulator for the plants.


All of these elixirs have one thing in common, they all contain sugar.

A test was set up in a university laboratory to test the effects of the sugary additives. Using a hydroponic set up, 12 ounces of cola was added to 5 ½ gallons of water. The water used in this test contained a low level of nutrition, enough to keep the plants alive, but not enough to really get them growing. After about two days the plants had a tremendous increase in bacteria growing on their roots. These bacteria didn't help the growth of the plants.

Another experiment conducted in Britain in 2005 looked at the various types of sugars including fructose, glucose and sucrose to see whether the addition of any of the sugars to irrigation water at the time of transplanting would benefit the plants. The researchers did discover that fructose, glucose and sucrose did speed up root development of the test plants, when applied at a concentration of between 3 to 10 ounces of sugar per gallon of water once a week for four weeks.

You should consider that this experiment was an isolated incident. Applying sugar will increase the bacteria which may have a negative effect on your plants also, but there is evidence that when plants root system has been highly compromised such as during transplanting a few applications of sugar may help to stimulate root development.


Sources of sugar should not be considered a good way to encourage root growth under normal growing conditions; they are likely to increase bacterial growth that could be hazardous to roots. However in cases for example where the roots of trees or shrubs have been cut, there is evidence though far from conclusive that sugar might help to encourage root development. The researcher was asked whether or not he might consider applying sugar to a newly planted Japanese Maple in his yard; his comment was not a chance--at least not until more research has been conducted

The Myth:
Salt is a good herbicide in the garden.

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The Facts:
Salt is one of the oldest herbicides known to man; actually salt and ashes mixed together was used quite extensively as an herbicide during Roman times. During the third Punic war, salt was used by the Romans to sterilize the food fields of the Carthaginians.

Salt is usually applied to the soil in high concentrations to kill weeds. It is normally used as a solid, without dissolving it in any liquid.

Salt works by drawing water out of plant cells, by doing so causes the plants to dry out and eventually die. Salt is a contact herbicide, it does not travel in the plants vascular system and will only affect the part of the plant that it actually touches. If salt is used as a spray it's likely to kill the shoots of the plant and leaves but the roots will remain alive resulting in the weeds sprouting again from the roots.

No matter how effective salt is at killing weeds it is very rarely recommended by horticulturists or other garden experts. Salt is potentially bad for your garden. If you just want to knock out a weed or two salt is probably fine, but placing it in large amounts in your soil is not a good idea because it may hurt other nearby plants or plants that you plan on placing there at some point in the future.

If garden experts don't recommend using salt on a regular basis as an herbicide it should give you some sort of idea how much damage it may cause in your gardens.


I'm going to salt my popcorn and find some other solution for the weeds in the garden.

In closing, I expect some of you might disagree with some of these findings. However remember that this research was done in reputable university labs under controlled conditions. Each of us will draw our wn conclusions.


  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
Micro Elements Indy 4 45 Jan 23, 2013 12:03 PM
Salt theolderchick 1 17 Jan 23, 2013 6:52 AM
sugar smells yucky! carrielamont 0 19 Jan 18, 2013 7:31 AM
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