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SKIP RICHTER: More common gardening myths

SKIP RICHTER: More common gardening myths

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The gardening world abounds with claims for products and practices that have little to no research to support the claims. Sometimes there is a grain of truth, but it is stretched or misapplied to the point of untruth. Here are few that you may have heard.

“Apply pruning paint to tree wounds to prevent decay and promote healing.”Logic would suggest that sealing a new tree wound would protect it and keep out water, right? Several decades ago, Alex Shigo disproved the “painting wounds” myth through extensive studies of how a tree responds to pruning and natural wounds. He determined that “painting” wounds doesn’t promote healing and prevent decay, but in fact the opposite can be true.

Coating the wound limits needed oxygen to the callous tissues that begin the process of closing over the wound. Coatings also trap moisture inside, speeding wood rot problems.

If, however, you live in an area where oak wilt is present, and are pruning oak trees, apply a sealant immediately after making the cuts to exclude the beetles that can spread oak wilt, and which are attracted to the smell of fresh wounds.

‘Houseplants will purify the air in your home and add oxygen.’It pains me to debunk this myth because I like it so much! Most claims reference a NASA study years ago that indicated some houseplants may remove a few volatile organic compounds such as benzene.

However, the devil, as always, is in the details. Most plants included in the NASA study had little to no effect on removing the handful of compounds studied (among the numerous pollutants in our air).

In a small, enclosed chamber, the presence of a few houseplant species made a positive impact on certain compounds. But in additional studies, when they removed all of a plant’s leaves before putting it in the chamber, they had almost the same result, indicating that soil microbes in the pots were accounting for much of the benefits.

Considering the thousands of cubic feet of air space in a home, any slight positive effect from a few houseplants becomes almost insignificant. According to John Girman, former senior science adviser at the U.S. Environmental Protection Agency’s Indoor Air Division, a 1,500-square-foot home would need 680 plants to accomplish the selected benefits found in the NASA study. Tarzan would certainly feel at home!

Nevertheless, there is a growing mountain of research pointing to the psychological and cognitive benefits of having plants around us. They beautify our homes, promote a sense of well-being and are beautiful, too.

‘Add a handful of bone meal to planting holes before planting roses and bulbs.’Bone meal is a slowly available source of phosphorus. Plants need phosphorus, but you should have your soil tested to know if more is needed. Phosphorus is often high in fertilized home gardens because it can build up over time.

In high pH soils, many sources of phosphorus are tied up and unavailable. One thing right about this myth is that when phosphorus is needed, putting a concentrated handful below the plants or in a shallow trench alongside plants (called banding) helps to ensure more is available, compared to mixing into the beds where the scattered application is more easily tied up.

‘Gypsum will break up and improve clay soil.’Rather than untrue, I should say, “It depends.” Gypsum is calcium sulfate. Sodium can affect the structure of a clay soil, causing it to not drain well. Gypsum can help remove the sodium from the soil particles so it can be washed away, leaving the soil able to rebuild good internal structure. If your clay soil is tight and poorly drained due to sodium buildup, gypsum can help. If not, it only amounts to a calcium and sulfur fertilizer, and many soils already have more than enough of those two nutrients.

“If a pesticide is organic, it is safe.”In very general terms, most organic products may break down faster in nature than most synthetic products, and the more toxic organics are no longer on the market.

But organic pesticides can, like synthetics, pose health risks to people, bees and other beneficial insects.

Even insecticidal soap can kill several types of beneficial insect larvae.

Pesticides are made to kill living things, or to severely disrupt their functioning, whether they are produced naturally in plants or synthetically in a lab.

All pesticides should be used with caution and as a last resort after all other good horticultural practices have been utilized.

When used according to the label, the danger to people and the environment can be minimized. But misuse of a product that is natural or organic under the assumption that it can’t cause harm is a serious error.

Robert “Skip” Richter is the Texas A&M AgriLife Extension horticulture agent for Brazos County. For local gardening information and events, visit Gardening questions? Call Skip at 823-0129 or email

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