Water softener discharge and plants

One of our customers had this question – we thought it would be interesting to post:

When we built our house seven years ago, the builder ran the discharge tubes for our softener out near an established oak tree, saying the water would be good for it. We live in rural central Texas, where the soil is sandy and drought is the usual climate. This spring, I diverted the water to a point outside the tree’s drip line, and within a few months the oak’s leaves turned brown and began falling off, even though there was ample rainfall. I returned the water to its old discharge site, but with no response from the tree. The grass and weeds, however, show no ill effects from the water, and in fact seem to thrive where the water is.

I have queried the county agricultural agent, master gardeners, a high school science teacher, a nurseryman and ordinary locals, and no two have the same explanation or remedy.

What’s your guess?

Did the tree like the water well enough to ignore the salt, and reacted to the loss of water?
Did it just take seven years for the salt to build up in the soil enough to damage the tree?
Is the ground likely to be so salty now that the tree is lost?
Do I need to flush the soil with (precious) fresh water to dilute the salt and migrate it away from the tree?
Should I keep the water on the tree because the salt content is too low to be a factor?

I realize you can’t do a detailed diagnosis from my brief description, but you know more about it than I do, and everyone here seems to just do a lot of head-scratching.

Thanks for whatever advice you can offer.

Answer: Trees seem not to have any negative response when nearby water softener discharge.  The reason for this may be that while the first few gallons of discharge do contain a significant amount of salt, the remaining discharge volume (~40 gallons to 70 gallons) is fresh water, and this dilutes the salt solution considerably.  Many applications use water softener discharge for irrigation purposes with no apparent ill effects.

However, you can also consider using potassium chloride rather than sodium chloride.  Potassium is a nutrient and fertilizer as well – good for plants.  Our water softeners are able to use either sodium chloride or potassium chloride salt, and work well using a wide variety of salt brands.  If you decide to use potassium chloride, we always recommend that you purchase potassium chloride purified for use in water softeners (available at many supermarkets, plumbing supply and hardware stores). Non-sodium potassium chloride is commonly available and sold under the brand names Morton KCL, K-Life, Softouch and Nature’s Own.

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