There are several ways of potting up - do call if you are unsure of any of the below and we will be happy to talk you through the potting process:
1. You could mix a small quantity of plaster of Paris (or cement) and put it into your planter (do be careful if using a ceramic or terracotta pot as plaster expands so do not use alot), when it is just about going 'off' stand your tree / plant in at the required height and wait for it to set. Once this has set, you can dress the top with gravel or slate, moss or bark chippings, whatever you preference. To have a secure crust of gravel or slate you would need to coat it in PVA glue, spread on the surface and leave to dry (about 5 hours).
2. You could use expanding foam (available from our website or most DIY stores) in a similar way to the above and then dress as above. This is the method that we use and is probably the easiest, and by far the cleanest!.
3. An easier option would be to stand your tree in your planter and then simply fill with earth, sand or gravel.
If your trees are going to be placed outdoors, you will need to have the planter weighted against the wind so we would advise you to use option 1 or 3 for potting or just fill the bottom of the planter with stones.