There’s an old saying in the Upper Midwest: If you haven’t heard a rumor by 10 a.m., you better start one. It can be humorous how stories get circulated, or how information gets changed as it passes by word of mouth. Maybe that’s how rumors and myths of houseplant care originated.

Much factual information is passed along about houseplant care, both verbally and written, but there’s a fair amount of fiction as well. Practices that have been disproven by science are best discontinued from our houseplant culture.

I might mention, though, that debunked methods don’t necessarily mean a plant will quickly die outright. If you’re currently doing one of the methods frowned upon, but your plants are beating the odds, by all means keep doing what you’re doing. But given the opportunity, it’s best to avoid these practices.

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Here are 10 houseplant myths that have been proven false.

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  1. Houseplant pots should have a layer of rocks in the bottom for drainage: This misconception just won’t die. Even the best gardeners, like my Mom, always layered rocks or broken pot chips inside the pot before adding soil. Multiple research studies have since shown that when water meets this layer of change, it first super-saturates the potting soil before passing into the rock layer, which can contribute to overly soggy soil. The best drainage happens when the pot is filled top-to-bottom with high-quality potting mix. We can discontinue all layers of drainage material.
    Potting soil actually drains better without a layer of rocks in the pot. David Samson / The Forum
    Potting soil actually drains better without a layer of rocks in the pot. David Samson / The Forum
  2. A coffee filter or diaper placed over the drainage hole inside the pot prevents soil from leaking out: Coffee filters and diapers can both become clogged, making matters worse. I’ve never had a problem with high-quality potting mix seeping out the pot’s bottom. We can skip the liners.
  3. Plants shouldn’t be in bedrooms because they release carbon dioxide at night: I remember my mother saying that part of her nurse’s training in the late 1930s was removing all plants from patients’ rooms each night, fearing the effects of the carbon dioxide given off at night through the respiration process of plants. However, this gas is so highly diluted that plants were long since deemed safe in bedrooms.
  4. Plants grow bigger if planted in bigger pots: Inaccurate, because a small plant in a large pot wallows uncomfortably in the too-large soil mass. Instead, gradually increase the pot size as the plant grows.
  5. The NASA clean air study proved that houseplants purify the air in a house: Houseplants absolutely create a healthy environment, but they can’t purify home air the same way plants purify a small, closed space capsule. Research showed an average home would need 680 plants to remove air toxins comparable to the NASA space study.
  6. Milk or mayonnaise can be used to shine plant leaves: Although these products create a shine, they can also block leaves’ natural pores. Simply dusting, or wiping with a damp cloth, is healthier.
  7. Yellow leaves mean a houseplant is overwatered: Although that’s one cause, yellowing leaves can also mean lack of light, too little water, rootbound, insects or disease.
  8. Houseplants need watering once a week: Not necessarily. Watering frequency depends on plant size, pot size, air humidity, season, soil type and room temperature. Instead of watering routinely on a weekly schedule, it’s better to check them weekly, but water only if needed.
  9. Succulents need only a little sip of water at a time: Wrong, because succulents should go long intervals between watering, allowing the potting mix to dry thoroughly, but when water is applied, the entire soil ball should be moistened.
  10. If houseplants are looking sickly, maybe fertilizing will help: Fertilizer is not medicine for sick plants, and force-feeding can make matters worse. Fertilizer provides nutrition for healthy plants — and if plants are ailing, other causes usually need correction first. Fertilizer is best limited to the active growing season when days are longer, from March through September.

Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at donald.kinzler@ndsu.edu.