How we pot the topiary balls up is using expanding foam.
Initially weigh down the planter by filling it to within an couple of inches from the top with soil, bricks, rubble etc.
Them spray expanding foam on top of this, if you then sit your ball on top, the foam expands up inside the mesh framework of the ball and sets solidly. This method will ensure your topiary is firmly secure in your planter.
It is the same foam that is used for wall cavity insulation so you can either buy locally or we sell this on our website. You only need to use this in the top section of your planter that comes into contact with the topiary ball.