Contact: Diane Relf, Extension Specialist, Environmental Horticulture
Posted April 1997
Myths abound in the lore of gardening, clouding issues and veiling the truth. The following are some common gardening myths.
***MYTH*** Botanical insecticides are natural products toxic to pests but harmless to other living things.
Nothing could be further from the truth. Plant-derived poisons are only sometimes less toxic to man than synthetic agrichemicals.
Rotenone, from the roots of derris plants, is toxic if swallowed or inhaled. Both pyrethrum and rotenone are low in toxicity to mammals yet highly toxic to fish. The yardstick for comparing acute, short-term toxicity is the LD50 or lethal dosage needed to kill fifty percent of a group of test animals (rats, rabbits, etc.). When you compare LD50 figures, the chemical insecticides malathion and sevin rank safer than nicotine sulfate, a botanical poison derived from tobacco.
No matter whether the chemical comes from a laboratory or a plant, it pays to be careful.
***MYTH*** Fall is the best season for pruning.
This is false for several reasons. Shrubs and trees store carbohydrates (food materials) in their branches and leaves, so fall pruning can reduce their cold hardiness.
Azaleas and other spring-flowering plants would bloom poorly if pruned in fall, as next year's flower buds are present at that time. Such plants are best pruned in spring right after petals fall.
***MYTH*** The soil under oaks and pines is acidic.
This is sometimes true, sometimes false. The acidity of soil depends not only on the nature of vegetation growing on it, but also on the type of rock below. Some soils under oaks and pines are neutral or alkaline, needing no lime.
***MYTH*** Mushrooms and toadstools sprouting in your lawn means that the soil is deficient.
In actuality, these plants are merely the above-ground growth of fungus organisms living in soil. Some fungi live on buried lumber, dead roots, or fine particles of organic matter. Others live in harmony with tree roots, assisting in the uptake of water and nutrients. A few cause plant disease. The sudden appearance of mushrooms does not mean the lawn needs lime, fertilizer of anything else. If you object to their sprouting in lawns or gardens, use a rake to dispose of them. There is no chemical control for mushrooms.
***MYTH*** Moss growth in lawns shows a need for lime.
This is not necessarily true. Acidic conditions could be responsible for moss crowding out your grass, but so could excessive shade, poor drainage, low fertility, and a host of other causes. When conditions do not favor healthy turf, moss can take over.
***MYTH*** When it comes to garden chemicals, if a little bit is good, a lot is better.
This myth is not only false but dangerous. Doubling or tripling the dose of any garden input can have disastrous results. Weed killers used in this manner can injure plants you never intended to harm, not to mention leaving long-lived residues in soil. Over-use of insecticides may kill beneficial bugs, harm plants, and render vegetables unfit for consumption. Doubling the recommended rate of any pesticide increases the chances of poisoning people by inhalation, absorption through the skin, and by other routes.
Fertilizers used too heavily will burn plants, prevent seed germination, and contaminate water resources. Even organic fertilizers such as manure can cause harm if you use too much.
(Prepared by Ellen Silva, Extension Technician, Consumer Horticulture, Virginia Tech, Blacksburg, VA 24061-0327.)
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