I have discovered that the reason my potted Ficus Benjamina was looking so great is that the roots had escaped out the bottom of the pot and deep into the ground. How do I cut the escaped roots without killing the plant? I want to repot it back into the same pot. Is this possible? How do I best proceed?
Ficus have vigorous roots that will readily grow through drainage holes in a pot. Springtime is the best time to try to repot Ficus. Ficus are quite hardy plants the success will depend on the quality of the root ball in the pot. If the plants loses all its leaves after transplanting don't panic, this is a response to transplantation and doesn't necessarily mean the plant is dying.
You will need to cut the root from the bottom of the pot, a pruning saw is likely to be the easiest method. This done you need to remove the plant from the pot, this can be quite difficult if the root ball is very compacted and you want to save the pot, try placing pot in large container of water. Allow all the air bubbles to rise to the surface and the soil to be drenched, you should then be able to gradually loosen the root ball.
Once you have taken the root ball out of the pot you will need to loosen the roots and prune any large circling roots and leave all the smaller fibrous roots.
Use new potting mix and pot the plant to the same level as before. It is a good idea to prune the upper parts of the plant to encourage new growth. Water immediately after transplanting with a Seasol mix this will help reduce transplant shock. Water regularly when the soil feels dry ( test with you finger). Fertilise with a liquid fertiliser every few weeks in spring and summer.
Good luck