We have received a confirmation from TFL that planting around trees can remain. The condition is that the flower beds/ soil should not be highly raised, because high soil can damage the bark of the tree. they say.
This means if there are more volunteers happy to plant and water in Swinton Place or Acton Street, you can plant within those conditions.
Another condition, by the way, is that no bricks should be used for wall-creation or fencing around the plants.
The email by TFL is held by Daniel.