Is it true that plants will not grow if watered with microwaved water?
No, it is not true. If you water plants with water that is too hot you can damage the roots, but that is a function of heat, not whether or not the water has been specifically exposed to microwaves. Microwaves do not change the structure or composition of water; all they do is add energy, same as boiling on a stove. Assuming you let the water cool, it behaves like any water.
