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A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

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Tuesday - December 04, 2007

From: Phoenix, AZ
Region: Southwest
Topic: General Botany, Watering
Title: Effect of epsom salts and gray water on plants
Answered by: Nan Hampton

QUESTION:

We live in Phoenix where water is a precious commodity. We have decided to use as much of the gray water as we can for watering our garden, shrubs and trees. One of the suggestions we heard about was to use the water from the bathtub. We were wondering if the Epsom Salts(magnesium sulfate-MgSO4.7H2O) that we use in the bath water is harmful to the plants and/or trees?

ANSWER:

Well, unless the concentration of epsom salts in your bath water is very high, it will probably be beneficial to your plants. Both magnesium and sulfur are necessary plant nutrients. Plants need magnesium for the production of chlorophyll and, therefore, it is necessary for photosynthesis. Magnesium is also important in activating many enzymes. Sulfur is a component of some amino acids and is also a component of some enzymes. You can read more about the effect of epsom salts on plants in:

What is the effect of epsom salt on a plant? and How does epsom salt affect plant growth?

Generally, the level of each of these nutrients in soils is high enough for the plants' health. However, sometimes soil has low levels of Mg and/or S and, in that case, epsom salts are recommended as a fertilizer.

You can see recommendations from basic-info-4-organic-fertilizers.com for proportions for the application of epsom salts as a plant supplement. You can compare these proportions with the concentration of epsom salts in your bath water. If your bath water isn't more concentrated, then your plants will probably benefit from its application—not only for the moisture but for the added nutrients as well.

 

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