Hello Francisco,
Many thanks for your detailed reply. Winter is nasty here but after april 15, the weather is good until early November. Since april 15 I have had 66 days over 21 °C (70 °F) or greater, of which 32 days at temperature of 27 °C (80 °F) or greater. Not like Portugal weather but manageable. Cuttings done this winter of Malta Black, Chicago Hardy, Bisirri #3, Italian Everbearing, Improved Celeste and Petite Negra have grown over 3 feet since mid-april.
Regarding grafting, I am amazed that you found the Extension Service of the University of Minnesota. They have done tremendous work improving apple, pear, peach, plum trees and grapes for cold regions. We have over 50 commercial wineries now because of the University's research on grapes. But unfortunately fig is not a fruit on which they have done any research. The demand for fig growing in Minnesota is non existent. There was only one other member from Minnesota on this forum and she does not have a single plant anymore. I have sent her a PM to offer some of my rooted cuttings to get her started again, but no response yet.
I am glad you think that grafting from green scion could work. In my reading on what is available on grafting on this forum, I had gleaned that some members were grafting during the summer and assumed that they used material from green wood. I should look for some variety that I don't have.
We still have 12 weeks of growing weather; so it would be worth my while to try grafting this summer.
Best wishes for a hefty fig diet this summer! Personnalyy I am looking to possibly a good crop of Petite Negra and a couple of figs each on 4 large cuttings of Malta Black and a Bisirri #3.
Marcel