Softened Water Can Cause Hard Times For Indoor Plants

UNIVERSITY PARK, Pa. -- If your indoor plants or plants brought in for the winter seem to be faring poorly, a Penn State horticulture expert suggests taking a hard look at softened water as the culprit.

"There isn't any research that tells us which plants can be injured, but plants do have a widely varying tolerance for softened water," says J. Robert Nuss, professor of ornamental horticulture in the College of Agricultural Sciences. "In many cases, water from a mechanical softener has a harmful effect on plant growth."

Nuss explains that hard water contains large amounts of calcium and magnesium, which are plant nutrients. However, these minerals reduce the lathering effectiveness of soap when clothing or other items are washed. "The minerals in hard water often combine with soap to form the ring you see in bathtubs or wash bowls," he says.

Many homeowners soften their water by using a filtration system to exchange the calcium and magnesium in the water for sodium, creating a softer water that allows soap to function better.

"Sodium is used by plants only in very small amounts," Nuss says. "Over long periods of time, sodium becomes toxic to plants."

Nuss says excess sodium will damage the soil quality around the plant's root system by breaking down the soil structure, thus reducing drainage. Nuss says savvy plant lovers can save their plants by using several care methods.

-- Leaching. By using rainwater or unsoftened water to water your plants, high levels of sodium can be leached out of the soil.

-- Elevation. By placing your plant on gravel or a similar material, a reservoir is formed to collect water passing through the soil. "Never allow plants to stand in softened water," Nuss warns.

-- Repotting. Fresh potting soil will provide a new environment for the roots, free of excess salts.

Other water additives used by municipal water systems, chlorine and fluorine, also can harm some plants. Nuss says they are trace elements that are needed in very small amounts to keep plants healthy. "In excess, like sodium, they can be toxic," he says.

Chlorine generally presents less of a headache for houseplants, Nuss explains. "Chlorine can be eliminated from water by heating, aeration or by filling watering containers and letting them stand overnight before watering the plants."

Fluorine can adversely affect plants at concentrations as low as .1 part per million. In some municipal water supplies, 10 times that amount is added to prevent tooth decay. "A top indicator of fluoride content is the spider plant, or Chlorophytum, which will show spotted leaves or burned tips," Nuss says.

Houseplant gardeners can deter the effects of fluorine by adding two teaspoons of limestone per six-inch pot of soil. The addition of lime raises the pH of the soil and combines with fluoride in a form that plants cannot use, according to Nuss.

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EDITORS: To contact Robert Nuss, please call 814-863-2196.

Contacts: John Wall jtw3@psu.edu 814-863-2719 814-865-1068 fax

Last Updated March 19, 2009