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.
The Myth Soil acidifiers such as sulfur, iron sulfate, and aluminum sulfate can be used to lower soil acidity.
The Facts Soil acidifiers do indeed contain compounds that will reduce soil pH. This will result in increased uptake of nutrients that are more available under acid conditions. Manganese and iron are the two most common elements unavailable to plants grown in alkaline soil.
If all you want to do is adjust the pH without adding fertilizer your best choices include sulfur, aluminum sulfate, and iron sulfate. The table below shows the amount of acidifers (in pounds) needed to lower the pH 1 level in various types of soils per 100 sqare feet,
Some may ask why you might want to use these compounds to lower the pH.
The most common reason is rooted in aesthetics: many gardeners like to change the colors of their hydrangeas by adding acidifiers. If you have a pink hydrangea and want to change it to blue you can add aluminum sulfate. On the other hand if you have a blue hydrangea and want to change it to pink you would add lime, which will raise the pH to an alkaline level and result in pink blooms. Understand however this is only a temporary measure; when you stop adding these substances, the plant will return to the original color determined by the pH of the native soil.
Another common reason is more practical. Plants such as blueberries, azaleas and rhododendrons prefer acidic soil. If your acid-loving plants are not doing well in their present location and a soil test indicates alkaline soil you may want to give acidifiers a try.
However caution is advised when using iron or aluminum sulfate these compounds are very strong and an over application can be dangerous for your plants. Aluminum can be toxic to your soil so you need to be especially careful not to over apply aluminum sulfate.
The Myth Tobacco and tobacco products are an effective insecticide.
The Facts History shows us that tobacco has been used in the garden for many years. The gardener to King Louis XIV wrote about using tobacoo products as an insecticide in a book published in 1690.
The usual way to apply tobacco to plants is to soak tobacco leaves, or chewing tobacco in hot water. The amount of tobacco varies widely between the old recipes, but usually anywhere from 1 tablespoon to a handful per gallon of water. After the tobacco has soaked for a certain length of time to water is filtered and applied to the plants often with a tablespoon of dish soap added to the mixture. The soap helps the mixture adhere to the leaves and stems.
If you would like to try a nicotine insecticide brewed the old-fashioned way: a recipe from 1915 recommends steeping 5 pounds of tobacco stems in 3 gallons of water for three hours, straining off the stems and diluting the mixture with enough water to make 7 gallons of spray.
Nicotine the active ingredient of tobacco is a nerve stimulant. It attacks the nervous system on the target insects to eliminate them. Homemade concoctions are likely to be effective and there are hundreds of recipes that include various amounts of tobacco. If you decide to try chewing tobacco, experiment a little. Figure out how much tobacco you need to add to the water to make a mixture that will be effective against your particular insect issue. But remember that the tobacco you use could be the host to the tobacco mosaic virus so be careful what you treat.
The Myth An effective insect repellent can be made from hot peppers.
Capsaicin the ingredient that puts the "hot" in hot peppers has been shown to be an effective repellent to insects. If you notice I said repel insects not kill.
A study done in 2002 indicated that whiteflies and mites were repelled for almost 2 months. These studies were conducted in a greenhouse so it is highly unlikely that the spray would last for that long in an outdoor situation. Capsaicin is likely to help control insect infestations especially mites and whiteflies.
Because it is a repellent rather than a poison, don't expect it to wipe out the pests overnight, or eradicate them for long.
Homemade hot pepper sprays will not be as effective as commercial sprays, primarily because commercial producers put more time and effort into making sprays than homeowners. Most commercial sprays include additives that allow the spray to stay on the plants for a longer period of time those homemade sprays will.
So if you're looking for an organic solution to a mite or whitefly problem why not give pepper spray a chance?
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 own conclusions.
About Paul Rodman
Paul 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.