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January 12, 2013

1 - Abutilon (Flowering maple) and many other houseplants suffer from the high levels of dissolved minerals in Southwestern well waters.

Yard and Garden January 12, 2013

Q.

I am sending a picture of a leaf from my Abutilon 'Red Tiger'? What was wrong with it? Many of the leaves are turning brown and drying around the edges. This is a house plant and has been protected from the cold weather.

D. Haney

Grant County

A.

Abutilon (the genus name) is commonly called "flowering maple". It is related to cotton (in the Malvaceae family), but because the leaf looks like a maple leaf it is called flowering maple. It is indeed a house plant and cannot withstand freezing temperatures. The symptom that you see – dead leaf lobes with the portion nearest the petiole remaining green, is a symptom of "salt burn". Mineral salts from the water (and sometimes from potting soil) accumulate in the pot and are taken up with water and nutrient minerals (excess nutrient minerals can also cause salt burn). These minerals are deposited in the leaves after the water transpires from the leaf (evaporates through the stomata in the leaf). As the minerals accumulate they reach a toxic level and begin to kill leaf cells. This happens first near the tip of a leaf (or in this case the leaf lobes) and along the margins (edges) of the leaf.

Salt accumulation is a problem with most houseplants irrigated with water from wells (municipal or private) in the Southwest since these waters often have very high levels of dissolved minerals. The solution to the problem often requires repotting when the mineral salts accumulate too much. When repotting, gently wash away much of the soil around the roots. This washes away those excess salts also. Then carefully work potting soil back in around the roots as you replant in a new or, washed and sterilized pot.

To slow the buildup of salts in the soil of houseplants irrigate sufficiently to allow water to drain away. The soil should be moist when irrigated so that the salts are already dissolved in water and easily washed away. Do not let the water that leaches through the pot reenter through the bottom of the pot, or the salts in that water will return to the soil. Drain the surplus (leachate) water. If the soil is dry when you water, you can water a little at a time to rehydrate the soil before watering to leach away salts, or rehydrate the soil by watering from below. This appears to be a violation of the rule not to let the water reabsorb through the bottom of the pot, but after rehydrating the soil to solubilize the salts, then irrigate from above with sufficient water to leach away the salts. Be sure to dispose of this leachate and do not let it reabsorb into the pot.

Whenever possible, water with rain water. I have been irrigating indoor houseplants for the last year with filtered water (that removed calcium and many other minerals, but not all minerals). This also reduces the introduction of excess mineral salts to the soil. When the houseplants are outside in the summer, I can irrigate with tap water that has a higher salt content as long as I leach the soils with each watering. Apply fertilizers to moist potting soils after they have been leached. Remember, fertilizers are also mineral salts that can accumulate, but they are also necessary for good growth of houseplants. Apply fertilizers appropriately according to label directions.

For more gardening information, visit the NMSU Extension publications Web site at http://aces.nmsu.edu/pubs/_h, or to read past articles of Yard and Garden go to http://aces.nmsu.edu/pubs/periodicals.html

Send your gardening questions to:

Yard and Garden, Attn: Dr. Curtis Smith
NMSU Agricultural Science Center
1036 Miller Rd.
SW, Los Lunas, NM 87031.

Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist emeritus with New Mexico State University's Cooperative Extension Service. NMSU and the U.S. Department of Agriculture cooperating