Posted: 27/07/2014 at 16:10
I'd trim the turf back so you have a neat circle of bare soil. You can then use this for feeding and watering your tree, and can mulch with well made garden compost in the autumn and spring to help conserve moisture.
Trees never do well with grass up to their trunks.
Some Cyclamen hederafolium or coum would look pretty there and wouldn't be bothered by the mulching