Sodium in water wreaks havoc on plants
: As a relatively new resident to the Las Vegas area, I am wondering about the white powdery buildup along the bottom of my walls and planters in my yard. Is it calcium from hard water? For a densely planted backyard, is there something that I can clean it off with that will not harm my plants, trees and shrubs? Is there a way to prevent it in the first place short of softening the water used through my drip irrigation system?
A: This is indeed salt accumulating on your wall from the irrigation water.
You do not want to use softened water for irrigation unless the salt used in your water softener is potassium-based. Sodium-based salts in the irrigation water will be extremely damaging to your plants over time and destroy your soil.
I am sure a large percentage of the salt is from calcium but not all of it. Unless you are on a well, you are using water from the Colorado River. If this is the case, then the salts accumulating on your wall would be a combination of calcium, magnesium, potassium, sodium and others formed as carbonates, sulfates, chlorides, borates and others. It’s whatever is in the Colorado River combined with whatever salts are in your soil. A real hodgepodge.
Besides the salts already contained in your irrigation water, the water picks up other salts as it travels through the soil to plant roots. These salts travel with the water as it flows through the soil. As water wicks up surfaces like your block wall it evaporates, leaving behind the salts contained in the water. These salts can be quite corrosive to metal, cement and other hard surfaces over time. The only good way to prevent this accumulation is to keep water away from walls, driveways, sidewalks and anything metal in the soil.
How far should you keep water away from these surfaces? I would recommend distances of 3 feet in sandy soils and further in heavier soils. Put drip emitters on the side of the plant away from walls and hard surfaces and let the roots grow in that direction.
I would keep turfgrass the same distances from walls and hard surfaces as well so irrigation from them does not harm these surfaces.
Many people who are on well water here do not have this problem due to the low salt levels in most deep groundwater.
Mild acids, such as vinegar, will work in removing these salts along with some elbow grease. It does not repair the damage done however.
Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by e-mail at morrisr@unce.unr.edu.