Right, the patent really only applies to propagating the plant for profit since they're never going to know if you just propagate it at home.
So if you have one plant, and you sell it to someone else without dividing it, that should be legal.
But if you divided it in half, kept half and sold the other half, then you have profited by propagating your plant and that would be patent infringement.
In the case of a patented tool or other device, though, since you can't "propagate" them, any copying of the tool so that you don't have to pay the patent holder for a new one, or pay him a royalty on the design is also patent infringement. We patented a tool a few years ago, and the patent applies to all tools of that particular - exact - design that we have made, whether or not they were made before or after the patent was granted.
