Q. In a past posting on your blog you mentioned that using 100% distilled water for container plant irrigation might mess with the potting soil. What did you mean by that?
A. Distilled water has no minerals in it. This can pose problems for soils and cause the soils to “deflocculate” which means the soils can start to seal and begin to slow the water movement through it by taking minerals from the soil particles.
So it is best to add just a small amount of fertilizer…very little… so that you replace the minerals that are no longer there. Think of it similar to drinking distilled water as opposed to water that has some “good” minerals in it and the effect on our bodies.
So good salts to use for replacing the salts taken out would be fertilizer salts from a good quality fertilizer or a light compost tea. How much to add? How much salt remains after water evaporates from irrigation water? Very little. A pinch or two of a fertilizer salt in a gallon is enough.