I've just planted a box hedge. I'm very chuffed with myself as they are all from cuttings I have taken two years ago.
What's a good fertiliser to promotet healthy roots this autumn? I've got some one year old leafmould to top dress.
Id say it's getting too late to start feeding; it will encourage new growth which will get damaged by frost. Just keep it watered and mulched and then in spring feed with tomato food.
A slow release like Blood, Fish and Bone in spring would be ideal. If the plants were strong and healthy when you put them in, and the ground well prepared, they shouldn't need much attention till then.
The odd foliar feed (seaweed is ideal) through the season can be beneficial