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Smart Garden 2020: The impact of Water Quality on Houseplant Care

Photo: Julie Weisenhorn, UMN Extension
Houseplants in Minnesota face a challenge with our long winters. I almost always think light is the limiting factor for growth and plant health in our state.  Water, however is a close second to what can limit plant growth. We talk a lot about when and how to water a plant, but water quality over time can be just as important.  

If you keep houseplants for many years or if you grow plants sensitive to chemicals in the water, it is important to understand how water quality can affect your plants over time. 

What do we mean by water ‘quality’?

Water quality can refer to chemical, microbial or physical properties. If you have a private well or spring water, you need to be concerned about all three of these, but for most of us using municipal water in growing plants, it is the chemical issues that are the major concern. 

Check your municipal website for what treatment is done to your water. In Plymouth, where I live, tap water is treated with sodium hypochlorite, a form of chlorine to minimize bacteria, fluoride for dental health, and the pH is 7.2-7.5.  

What chemicals can affect your houseplants? 

Chlorine, fluoride and pH can all affect your houseplants. 

  • Chlorine: It evaporates within a few days if you allow the water to stand at room temperature in a wide container. Most plants are not too sensitive to chlorine.
  • Fluoride: Some plants are sensitive to fluoride, especially those with long narrow foliage such as spider plant, Easter lily, dracaena, peace lily, parlor palm, prayer plant and freesia. Over time these plants will show brown tips from excess fluoride.

    Flushing the soil with rainwater or bottled water can reduce the buildup of fluoride. Fluoride can also be removed with special treatment, such as reverse osmosis, a system you can install in your home for a few thousand dollars. 

  • pH: Plants grow best with a soil pH of 5.0-6.0, so higher pH in municipal water, especially for acid loving plants such as citrus, can be an issue. High pH limits the availability of some nutrients such as iron; plants with iron deficiency are chlorotic and have leaves with green veins and yellow in between. High pH water usually does not affect plants grown in the ground outdoors as there is such a large volume of soil. But in a container, over time water pH can change the soil pH because its a small volume of soil.   

What to do about chemicals in the water

To mitigate high pH water, most water-soluble fertilizers make the water acidic, or you can simply add a few drops of acid such as vinegar or lemon juice to the water (1/4 tsp to a gallon). Overfertilization can lead to brown leaf tips as well, using half the recommended strength is a good idea. 

Eliminate the chemicals

  1. Chlorine, fluoride and pH can all be eliminated if you use rainwater, bottled water, or distilled water. Obviously, these options vary in price and convenience. 
  2. Collecting rainwater during the summer can give plants a break from municipal water. Plants sensitive to fluoride or pH that you have grown for one year and certainly those over 5 years old, will often be affected by water quality. 


Author: Mary H. Meyer, Extension Horticulturist and Professor
 


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