Here is a run down on the proper way to plant up a large pot. If you are going to spend good money on a pot make sure that the plant that goes in isn’t going to die on you after a few months/year. Begin by getting your pot and placing it on some plastic to keep the place tidy as you are going to spill compost.
All pots should have a hole at the base to allow for drainage of water, cover this up with a permeable membrane (Mypex) and cover with drainage stone or any fine stone that might be readily available to you around your house, even if its broken pots and bits of styrafoam it will help, its better than nothing. This will stop the water logging at the base of the pot and killing your plant
You then begin to bring the soil/compost up in layers, compacting as you go, its good practice to throw some slow release fertiliser in with compost and give a bit of water to take out the air pockets. Large pots like these can do with some irrigation wrapped around the inside. This will get water right down to the base of the plant when it starts to establish and avoids compost overflowing the edges of the pot. Make sure to kink and tie the end of pipe so that the water doesn’t run straight through to the base of the pot.
If you are potting on a plant now is the time to get it out of its old pot and size up the rootball depth for the new pot. You may have to be brutal with the old pot, this Acer was well rooted, as the pot was in bad condition I took a hacksaw to it. You may have to smash your old clay pot to get that plant out of there aswel. This plant wasn’t pot bound (roots wrapping around the shape of the pot on the inside) but if they are take a spade to these roots and chop them off, the plant will do better long term from it. This rootball was only about half the size after i had removed all the waste from the bottom and the compost fell off the sides.
Now bring up your compost until the rootball is just under the top of the pot. Make sure that the stem of the tree is roughly centered (check the crown of the tree also to see what looks good) and begin to pack the compost around the plant ensuring that it is well secured into position. As a general rule the pot should be a minimum twice the size of the rootball of your plant. At this stage you can add decorative stone to finish off the top of the pot. Large cobbles are better here as if weeds grow in gravel it mixes with the compost and can become unsightly over time. I would recommend finishing them level with the top of pot. They will sink slightly in time (even when doing the above steps) with watering etc and when they do they should be a good height. Remember to leave the irrigation pipe sticking out a small bit (this can be covered with a rock). All you have to do now is hook up the pipe for a few mins during good weather and your potted plant should thrive!
This process should be followed for all pots as it will ensure that you will get the most out of your plants. The irrigation might not be needed where Olive Trees/Tree ferns etc are being used but would do them no harm. Below is the finished product using Acer palmatum (out of leaf but its better to pot on in winter) and a spiral box.
Check This Post