Ask the Master Gardeners — Soft Water on Plants
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- November
- 22
Ask the master gardeners
Q: Why is “softened” water not good for plants?
A: Water softeners remove minerals, mostly calcium and magnesium, that cause water to be deemed “hard.” When water is hard, a myriad of difficulties can arise for a homeowner such as the occurrence of excess lime deposits and the frustration of soap not dissolving properly or at all. Therefore a water softener can be beneficial to everyday life for the homeowner. Most water softeners are briny, that is they contain salt such as sodium or potassium chloride.
Plants depend on a fragile mechanism called osmosis to survive. What happens in osmosis is that water passes by diffusion from a weak solution (high water concentration) to a strong solution (low water concentration) until an equality is reached between the two. In the case of a plant, the water from the soil (weak) into the plant roots (strong) provides the plant with the moisture it needs to survive.
When water that has been softened is discharged into the garden, the brine from the softener can alter the osmotic pressure that plants rely upon to regulate their water needs. This imbalance should be avoided.
— Judie Phillips, New Rochelle , master gardener, Cornell Cooperative Extension of Westchester
This entry was posted
on Saturday, November 22nd, 2008 at 6:00 am by Bill Cary.
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Bill Cary grew up in Louisville, Ky. His gardening was limited to growing parsley and impatiens on the windowsill of Manhattan walkups until the mid-1990s when he bought a rundown old chicken farm on 8 acres in the Hudson Valley. Now he spends his weekends chasing deer, hacking away at invasive shrubs and vines and wondering why he doesn`t have more meadow and less lawn.
Will a reverse osmosis system placed after the water softener correct this problem of osmotic pressure? I’m having some real problems keeping house plants alive and also a tomato plant that will be moved out doors during spring for an early tomato harvest.
Thank you,
HumbleGardener
Good question. Let me see if Judie Phillips has any thoughts.