JoAnne Skelly: Debunking molasses myths

I recently read a heated online article by Linda Chalker-Scott, Ph.D., from Washington State University regarding the purported benefits of using molasses in the garden or landscape (http://blogs.extension.org/gardenprofessors/category/amusing-facts/). I had never heard of using molasses in the yard, so I was intrigued.

Many online sites that offer soil-building and homemade pesticide solutions tout the advantages of using “horticultural molasses” in the yard. Horticulture professor Chalker-Scott doesn’t know what horticulture molasses is. Sites claim molasses builds up the microbes in the soil; works as a chelate for converting nutrients to more usable forms for plants; improves the flavor and sweetness of veggies and fruits; and controls insects and weeds. It sounds like a horticultural miracle cure. Products available at garden centers tempt the unknowing and the ever hopeful who want a silver bullet for soil health and pest control. Dr. Chalker-Scott calls it a “typical snake-oil pitch!”

Her numerous blog posts debunk many of the molasses myths. She heartily disputes the claim that “molasses raises the sugar content of plants” saying “this bold statement has no basis in reality.” Sugar can’t get through the protective outer surface (cuticle) of the plant, except by possibly going through the pores in the leaf surface (stomata). Even then, the amount that might penetrate is too small to have any impact. There is no scientific evidence that it makes fruit sweeter. No research supports the claim that molasses makes nutrients more available to plants. While she discredits those claims, she does state that soil microbes will increase when exposed to simple sugars, such as those in molasses, because “microbes love carbohydrates.” This supports the possibility that molasses may help soil in that regard. However, field applications don’t provide much evidence.

“The insecticidal claims are nonsense,” she writes; although molasses can work as bait for poison. Chalker-Scott rails against online sites that support spraying molasses on the entire yard with abandon, since it must be safe. She calls this “one of the most reckless pieces of advice she has ever read.” If molasses kills anything, it is a pesticide; and it is never wise to apply a pesticide carelessly. There is some evidence that too much molasses binds up calcium in soils. This can help weeds thrive. Molasses may also burn plants.

Before you try unusual pesticides and magic potions, whether homemade or purchased, determine if the claims made about them are accurate and backed with scientific evidence.

JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension and may be reached at skellyj@unce.unr.edu or 887-2252.