Softened Water & Plants

What’s in it?  -  Different Kinds?


   Garden-Tip 1064

Gardening Tips for successful and beautiful Landscapes and Gardens


What is the chemical process of the water softener?

.....The water softener acts on the principal of ion exchange. Ions are atoms or groups of atoms that can gain or lose electrons in water and, thereby, exist in water with an electrical charge. Hardness exists as calcium (Ca++) and magnesium (Mg++) ions in water.
.....Ion exchange is a reversible chemical process in which (for salt softeners) sodium (Na++) ions from the insoluble solid medium (the ion exchanger resin) are exchanged for the calcium and magnesium ions in the water. The physical structure of the resin is not affected.

Water Quality Association -


Softened water for plants?

I am installing a water softener at my home. Can I use the water on outside plants and new fruit trees?

It depends on the type of water softener. Some work by replacing calcium and magnesium in the water with sodium by adding rock salt. In this case, the sodium concentration of the water may be hard on some plants and sodium will build up in the soil over time, causing degradation of soil structure. Some water softeners have valves that allow the water to temporarily bypass the softener. It is also possible to make a separate line to the outside tap so plants can be watered with unsoftened water. Although this adds cost, it is generally the best solution to the sodium problems associated with water softening. I would contact the company installing the system to see what type of process is used and what the levels of sodium or potassium are likely to be in softened water. According to some references, water containing more than about 1.25 milliequivalents of residual sodium carbonate per liter may cause problems with certain types of plants if used for irrigation. Another value sometimes used is sodium absorption ratio (SAR). This value, which factors in the relative amounts sodium, potassium and magnesium, is commonly included in water analysis reports. If it is less than 10, the water is considered safe for irrigation.

Remember, despite the fact that some makers of K-lite claim it supplies an essential element for plants, using this new potassium based salt instead of sodium chloride is not any safer for container plants. Water softeners are replacing what had been a rather insoluble salt(s) with one that is very soluble and has the potential to produce salts damage to the roots over time.


Chris Starbuck
University of Missouri

State Extension Specialist



Water softener bad for plants?

Is it true that water from my water softener is damaging my plants? A friend told me that the reason I can't grow houseplants is because I have a water softener.

Your friend may be correct. While there are many factors which make growing houseplants difficult, softened water can indeed be a cause of problems. If your water softener replaces calcium and other "hard water" minerals with sodium, a common means of softening water, then it is indeed causing problems when you water your plants with that water. Sodium, though needed by some plants in very low amounts, is toxic to plants at slightly higher concentrations. As you water the plant and the water is used by the plant, the sodium enters the plant. As the water evaporates from the soil, the sodium concentrates in the soil. Over time, the concentration of sodium causes the problem to get worse as sodium levels increase.

There are potassium-based water softening systems which may cause less problems. In these systems the hard water minerals are replaced by potassium, a plant nutrient that is beneficial to plants. However, as the potassium accumulates in the potting soil, it too can reach levels which are damaging. Potassium can accumulate to higher levels before the problems develop. Proper leaching of salts (potassium and other salts) from the potting soil frequently, and repotting before injury occurs, are ways to have softened water and avoid the problems.

There are other methods of removing hard water minerals from soil. As long as plant toxic minerals are not added to the water, they should cause no problems.

In many cases the easiest solution is to just use water from a faucet that receives unsoftened water. In New Mexico ground water usually has high mineral content, but only in some areas is the content high enough to cause plant injury. However, leaching the salts from the soil on a regular schedule is important.


New Mexico State University


Very few plants do well with high levels of sodium, and plants generally require an adequate supply of calcium and magnesium in order to thrive. So, these represent two reasons that soft water is not recommended for plant health. However, the amount of calcium and magnesium that exist in tap water are often not very significant. If the water has too little general hardness (< 3 degrees dH), calcium and/or magnesium may be in short supply. This can be remedied by adding calcium and magnesium sulfate in small quantities. When using Reverse Osmosis water on your plants, remember to include a micro nutrient tonic like Dr Q’s to replace those missing trace elements.






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