My experience with juniper cuttings in zone 5 is that it will take about 18 months to form roots, but the cuttings will persist, and then root and grow. So don't despair if you don't see roots on the junipers in only 6 weeks. Yes, winter cuttings are recommended, but I have had success with summer cuttings too, not 100%, but over 25%.
Oak cuttings, I tried a few times with no success. Your experience is not too different than mine.
M. Dir in his 1987 edition "Reference Manuel of Woody Plant Propagation from Seed to Tissue Culture", says the entire genus of Quercus has a reputation of being impossible to reproduce by cuttings in a commercial quantity. He goes on to state a researcher in Texas had success rooting cuttings of Quercus virginiana in May, August and the warm early days of October. Cuttings taken in cooler weather November to April failed to root. Cuttings from young trees, less than 8 years old, rooted more easily than cuttings from mature trees. Cuttings from mature trees were near 100% failure. 10,000 ppm K-IBA solution was used. Semi-hardwood cuttings were used, pencil thin or thinner. Well drained perlite & peat media, bottom heat. A polytent was not satisfactory. Cuttings were held under mist for 12 weeks then hardened off under reduced mist. Juvenility of the cuttings was essential. Cuttings taken from previously rooted cuttings achieved highest success at 81% (my note: implying the original batch had significantly less than 81% success). Dirr suggests that this approach might be extended to species beyond just Q. virginiana.
So from the books, the closed container was probably a bad idea. Bottom heat would have helped. And there was a specific concentration and component for the rooting hormone.
All in all not surprising you had no success, but also pointing out that it has been done and documented by at least one dude on one species.
The book goes on to discuss seed propagation of oaks, and grafting to propagate oaks. Grafting has a few tricks and suggestions, not a highly successful method for reproducing oaks, but much more successful than cuttings.
Take it from there. I have not seen anything since this 1987 publication to suggest anyone has worked out a system for rooting cuttings that was easier, or had a higher success rate.
