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Readers ask: Should you put mayonnaise on your houseplants?

  • Author: Jeff Lowenfels
  • Updated: November 2, 2017
  • Published November 2, 2017

A reader asked about the connection between the microbes she wants in her soil and the use of tap water that contains chlorine. This is added to water to kill harmful microbes, so it must be doing the same thing to soil microbes.

Actually, the chlorine in water has a surprising low impact on soil microbes. This may be because it evaporates out of the water fairly fast. Just to be safe, why not fill a container with water and let it sit for at least a couple of hours before using it.

The bigger problem should be a second addition to water, chloramine. This chemical does not evaporate out of the water. Fortunately, organic materials in potting mix "complex" it up so that it won't affect microbes. This means if you are using a soil-based system, everything is neutralized insofar as these two chemicals are concerned.

Using a hydroponics system, however, can cause problems, as there are not enough organics sometimes to take care of the chloramine. In this case, simply adding a bit of Tang will do the trick without harming your plants. The amount depends on the amount of water in your system. Look it up on the internet.

Next is a often-asked question about the use of mayonnaise as a leaf cleaner. (Winter brings out some strange questions, which is fine!) I am not sure where this silly idea came from, but it is not a good one. There is no benefit to using the mayo on your leaves, and it may even clog up stomata, which are necessary for the plant to take up water. Simply washing off leaves with a spray of water is all your plants will ever need by way of leaf cleaning.

How about white salts accumulating on clay pots? This can happen when the soil becomes "fertilizer saturated" and salts start to build up. My suggestion is to replace the soil after cleaning off the pot, inside and out. Soaking it in a sink for a hour will also help. You might want to even put it in a dishwasher for a cycle.

A reader writes that she has caladiums that are not looking too good. These "elephant ears" plants are terrific, but they sometimes need to go dormant. If you have some, let them die back by withholding water and placing the plant in a dark spot. In three weeks you can cut the leaves and stems back and pull the bulbs or leave them in the pot and restart in the spring. Store them with your fuchsia or in a dark, cool location until repotting them up in the spring.

I need to settle an argument before it results in a divorce. Paperwhites usually do not need cooling before you can get them to flower. These bulbs are sold "pre-cooled" so you don't have to go through the hassle. By the way, the old suggestion to plant in water that has a few drops of gin in it is silly. Alcohol kills roots.

Finally, someone wanted to know if I fertilize my houseplants. I do if they are actively growing. Those under lights for sufficient number of hours everyday will grow just as they do in sunlight. Feed them.

Those that are not under lights usually don't need much by way of feeding provided you have good soil. In any case, your plants will let you know if they need feeding. Just pay attention to them.

Jeff's garden calendar

Tom Paxton and the Don Juans at the Alaska Botanical Garden: There will be a meet-and-greet at 12:30 p.m. Saturday, Nov. 11, at the greenhouse. Free for those with tickets to the 7:30 p.m. show at Discovery Theatre, $10 for non-ticket holders.

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