As a general rule, where the patent is for a plant variety, only clonal propagation is prohibited, not sexual reproduction.
The monsanto issue was a patent on a particular piece of DNA that they had inserted into the genome of the plant, so they argued that any reproduction of that DNA sequence (including reproductive) would violate the patent.
So I would just say if it's a genetically modified plant, the patent owner might have a case for suing if you use it as breeding stock, but if it's just a normal plant patent based on regular breeding then you should have nothing to worry about, even if you intend to sell the resulting offspring some day. But you probably do want to get actual legal advice if that's the plan, as this was not intended to be legal advice!