About the only things that may become a factor with hard water is using some of the water soluble fertilizers. As it may not break them down as well. Also if you go into a drought period and the soil dries up, hard water may lack the surface tension needed to soak the soil. In other words the water could roll off the top of the ground instead of soaking in. As long as Mother Nature provides an occasional rain, I don't think you will have much of a problem.

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Mike Maier
aka
The Plant Doc