Samuel, I’d guess the plants you are starting with are sterile hybrids. They were propagated by tissue culture, not by seed. And more than likely they are patented (the original will be labeled with a “P.P. #”) because the breeders need to protect their investment. The same is done with roses and many other flowering plants. They are the product of many generations of hybridization with the goal of producing a beautiful flower, not seeds or robust offspring. Even the most skilled botanist could not get viable seed from them.

I have always wondered, how do they get these plants to be sterile. Do they do it through genetic manipulatIon? I mean, in order to come up with a great flower, you need to cross them. For that you need plants that produce good seeds.... no?

Some flowers are bred for such elaborate flower forms that they are unable to get themselves pollinated for one reason or another. I don't think there's much GMO work being done on ornamental flowers, and probably few or none for sale. This kind of thing is likely bred by old fashioned hybridisation.

Samuel, I won't insult plant breeders by trying to describe their work, but search online for anything related to "plant hybridization" and you'll see it's a matter of numbers, patience, luck and keen discernment. Once a desirable specimen has been bred or occurred spontaneously, it can be cloned or duplicated through cuttings (tissue culture) an infinite number of times rather than reproduced the old-fashioned way.

Thanks!