I usually wait until November and December to repot banksias but this year is warmer than normal so I have started to re-pot my Aussie natives a bit earlier this year. First up were banksias because they were not root pruned last year and the root balls were getting pretty solid.In the past I have found that banksia roots are very fine and fibrous. they also grow very fast and quickly fill the pot to the stage where water and air cannot penetrate into the root ball. Most of you will realize that trees cannot last very long in such a state. indeed, I lost quite a few before I worked out what the problem was. Now that I re-pot my banksias every year or 2 I’m finding that health and growth rates have improved greatly.
Here are some photos of the process I use when re-potting banksias.
First is a Banksia spinulosa. This one was field grown for 3 years but for the past 3 years in a 30 cm orchid pot.
Banksias have quite brittle roots. Rather than cutting with root shears I find it easier to grab a handfull of rootball and tear it off. When the root ball is reduced enough I finish trimming with the root shears then pot up with fresh mix.
Next is a Banksia serrata. This species adapts well to bonsai. They grow quickly, back bud readily even on very old wood and also continue to thicken even in a pot. Leaves can be a little large but do reduce somewhat with good pruning. Well worth trying for bonsai in my opinion.
The numbers on the pot are my repotting records and indicate that this tree was re-potted 27 Oct 2011 and again 11 Nov 2013. Each time I have cut back the root ball by about 2/3 – 3/4. Apart from where the mix has fallen out through the large drain holes of the orchid pot the root ball is a solid mass of fine banksia roots which need to be reduced to allow water and air to penetrate into the pot.