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Monday, September 17, 2012

Use Distilled Water or RO Water on House Plants

Q. I have a three house plants, a Christmas cactus, “Mother-in-Law’s Tongue” and an Orchid plant.  There is a white “fungus” looking on the top of their soil.  WHAT can I do to get rid of it?  Am I watering too much?  Indoors all the time.

A. It is difficult to diagnose without some pictures but this might be either a salt accumulation from using Las Vegas tap water coming from the Colorado Rivere or it could be fungus (mycelial growth) on the surface. Water taken from Lake Mead (Colorado River) at the Las Vegas location is carrying about six pounds of salt for every thousand gallons of water.

Our native desert soils also contain alot of salt. I assume your houseplants were potted with some commercial potting soil so the salt load is probably relatively smaller than our native desert soils. Over time this salt can accumulate in the soil (from the tap water and soil salt) and wick back to the surface of the soil as the water in the soil evaporates. This can leave a white crust on the surface.

Salt deposited on the soil surface from the Las Vegas
water coming from Lake Mead and soil salts left behind
when the water evaporates.
Remove the upper layer of the soil and repot the plant with fresh garden soil. Dilute your tap water with about 3/4 of the volume with distilled or RO water. I would not use pure distilled or RO water as this might cause some problems with your potting soils. Also when you water, make sure 1/5 of the water applied actually leaves the container out the bottom as drainage and discard. This helps to flush out the soil salts.

If this white thing is "fuzzy", this could be some fungal growth. Not all fungi are bad and some are decomposers and work to help break down organic materials that are already dead. Seldom do these fungi that feed on dead things attack healthy plants. Scrape off th surface, repot, keep air circulating around the plant and in sunlight when possible to help keep these fuzzies to a minimum.

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