Rego Herbam 15 : Make a tree blossom out of season, in a moment.
From this, could I make a dead branch from an apple tree bear fruit which I can actually eat?
I would say no. A dead branch cannot naturally bear fruit. With CrHe you could do it, but you would require vis to make the fruit nutritive.
Xavi
Nope, sorry.
The dead wood is, as you specify, dead. It can never bear fruit and so cannot be made to bear fruit with Rego magics.
Let me add my "no" to those of Tellus and Xavi. The Rego effect only applies to trees that could actually do the same thing "naturally" in due time. You cannot use it to make dead wood bear fruit, or even to make a tree of a type that does not bear fruit do so (I'm tempted to cite a willow as an example, but maybe I'm mistaken and willows do bear fruit?).