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Rose Myths

Dr. Tommy Cairns, ARS Past President and WFRS Past President

Dr. Tommy Cairns holds a PhD in Chemistry & Biochemistry and a DSc in Toxicology

Coffee Grounds as Mulch?

It has been suggested that coffee grounds make an excellent mulch or constituent of compost. Since grounds have all of the water soluble compounds extracted during the making of the coffee, the remaining insolubles are left behind, proteins, oils, lipids, triglycerides, and phenolics. Over the months the soil bacteriums do break down these compounds into humic acid compounds essential for soil fertility, but may induce a pH change from acidic to alkaline.

Yes, recycling coffee grounds can have a beneficial effect on soil fertility, but they should be used as a component of mulch thorough mixed with other materials such as barks and wood chips.

Vitamin B1?

For decades the myth of soaking bareroot roses in a vitamin B-1, or thiamine solution has been advocated without recognizing the science discounting its use. From a historical perspective, plant growth regulators called auxins [the naturally occurring indole buytric acid (IBA) and the synthesized napthalene acetic acid (NAA)] probably stimulated the unscientific belief that Vitamin B1 was a great substitute. Wrong! Plants can manufacture their own supply of Vitamin B1. The idea that B1 can stilumate root growth is misguided. However, the addition of IBA or NAA (Rootone) will be beneficial during the planting process.

Milk for Controlling Fungi?

In 1999 a South American study touted milk as an effective fungicide on zucchini. Imaginative gardeners then began the anecdotal dissemination of the news! Admittedly, the use of milk had been hinted at as useful for decades. However, there is no evidence that milk prevents black spot.

There is no evidence that milk sprays are effective in controlling black spot on roses. Foliage coated with a milk spray may be less vulnerable to aphid attack. While milk sprays offer an alternative to conventional pesticides for those who chose sustainable rose growing, they cannot offer a level of confidence of complete control.

Disinfect Secateurs?

There exists a fear amongst rose growers that diseases from one plant to another can be transmitted via the secateurs particularly at pruning time. For this reason alone, the advocates have suggested cleaning your tools frequently with Clorox bleach. While this act is a wise precaution, the choice of disinfectant is misguided.

The act of cleaning and sanitizing your tools may be beneficial, but Clorox tends to be damaging to metal surfaces and may cause pitting and eventual corrosion. An alternative available to the household is Listerene, Lysol or Pine-sol. And always wipe away any excess disinfectant before use on plants.

Phosphate in the Planting Hole?

Almost every book on roses contains the advice to place blood and bone meal in the hole before planting. This rich source of phosphorus as well as othernutrients is required since it is known to travel very slowly through the soil levels. Science has disputed some of these claims declaring there is sufficient natural phosphorus in the soil. While these statements may be factual true, the phosphorus is not in an available form for the plant to absorb. This myth has proven through the years to be a valid recommendation and continues to be good horticultural practice.

The Wonders of Epsom Salts?

Rose growers for many years have connected the application of Epsom Salts (magnesium sulfate) to increased production of basal breaks. Magnesium in the soil may not be in a soluble form available to the plants and so addition of a soluble form may be beneficial since magnesium plays an important role in photosynthesis. Scientific studies, however, discount this connection. Unless there is a severe magnesium deficiency in the soil, applying Epsom Salts will have little effect. And yet the results offered by many rose growers would seem to support the desired effects. Judicious applications may be used (intermittent, not regular) that ensure the plant has a sufficient source of readily available magnesium.

Organic Superiority?

Throughout history there are a number of myths about growing roses that are unfounded based on scientific facts. The most popular for ridicule is the mis-interpretation of “Organic”, recently renamed as “sustainable”. The popular belief lies in the mis-guided understanding of “natural” and “organic” products as superior to those derived by man-made chemical means. The consumer is constantly reminded that chemicals are bad and therefore organics preferred. Rose root systems are unable to distinguish the soluble nitrate ion derived from a compost pile versus a chemical fertilizer.

Nature as well as man can synthesize compounds containing Nitrogen, Carbon, Hydrogen, etc. Many toxic compounds are common in Nature as defense strategies. And yet man-made pesticides are labeled by those whose prefer “sustainable rose growing techniques” as dangerous to the environment. For the record, the Environmental Protection Agency (EPA) regulates these chemicals to be safe for use on roses when used according to the label instructions. The basic reason they are deemed to be safe is that an intensive review of the metabolism or decay of such chemicals is regarded as non-persistent, i.e. generally disappears in 21 days with no effect on the environment. Can the sustainable lobby claim that of the toxic components of their composts? To blindly take for granted that naturally derived compounds pose zero threat is both misguided and frankly dangerous.


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