Thanks for the question, Gilbert. Mowing around obstacles (to this day I hear this word in my head pronounced like it is pronounced in "O Brother Where
Art Thou?") is surprisingly easy. The short
answer is that you start by placing the chine (aka back, rib) of the blade at the blade's point against the post/trunk/whatever obstacle and then do a short stroke away from the post/trunk/whatever. Continue this all the way around the post, then back in the other direction to free this windrow from standing, uncut grass. This is covered in detail in my book, with illustrations.
The scythe is ideal for mowing meadow/lawn/field with obstacles in it (such as an orchard) when using this technique. In the Austrian Alps, it was once common (and is still to some degree practiced) to have pollarded
trees for leaf
hay interspersed throughout meadows, thus improving soil retention and stacking functions. These pollarded trees were/are mown around with the scythe.
There are other situations where I feel a string trimmer is more useful. I work as a stonemason and this past summer my colleagues and I took down and rebuilt a wall of an old one-room schoolhouse. We laid the face stones out in the
lawn in the order they were originally in the wall. Slowly the grass grew up in between all these stones and the string trimmer was very effective at mowing the stones free.
So, obstacles around which you can swing the scythe (trees, posts, a single stone, etc.): no prob. Obstacles where there's no room to swing the scythe at all (in the midst of a cluster or pile of stuff): other tools may be more appropriate.