Don't think it will harm the plants.
We have hard water...not a whole lot of iron but enough. In the house our very hard, moderately iron-ridden, water goes through a conditioner...but not for the outside water. What we have done is get one of those cannister-type filters and install it near the outside faucet so that all the water for the gardens passes through that filter. This cuts down on some of the residue, iron etc and prevents our sprinkler and soaker hoses from getting clogged with residues. Various types of filters are available for the cannisters but none actually will remove all the iron. But it sure helps!

Most hardware stores handle these cannister filters.
Jan

Maybe an electrical device will help? One unit might be located in the whole house and then you can connect the tap to get your water into tge garden.
But I'm not quite sure are there available in Minnesota as they are in the UK.