I have birch around my marketgarden, and nothing will grow about 10m away from them, they have enormous root system, they suck all nutrients and water out of the field. Maybe relocate them outside the field?
Well done, my garden is clay, and as you, very little rain for the past few months. I struggled to plant 20+ zinnias at the weekend. Just one thing though, do you think that you need rabbit guards on your trees?