Like any fruiter growing in a pot, blueberries need repotting from time to time. They can be a finicky plant, and any movement or repotting has to be timed carefully. If you’re going to pot up or re-pot a blueberry plant, it should only be done during its short period of non-flowering. Depending on the variety, this could be at any time of the year. The important thing is to do it while it’s not flowering. Blueberries do best in a very acidic soil, so before repotting you need to make up a new batch of acidic potting mix specially for them.
I have several blueberry plants which just recently had outgrown their 20 litre (20 quart) pots and needed potting up. What was worse, ants had started farming aphids on them, so I had to come up with a solution to fix that too.
You can see in the above photo that my blueberries are each sitting atop an upturned pot. This is for several reasons. Firstly, the pedestal enables me to work on the plants at my waist height, which saves my back. Secondly, it gets the plants up into moving air which helps prevent moisture-derived diseases. Lastly, it gets the plants up off the hot gravel, which is important for me in the very hot subtropical south-east Queensland summer.
When you’re ready to repot the first plant, carefully slide it out from its pot. Handling it gently, inspect the rootball for any signs of pest damage or ill health. The roots should look healthy & be of good colour. They should be evenly distributed, have no smell and not be overly root bound. Hopefully you won’t find any grubs or root rot.
Resist the temptation to to prune the roots or disturb them too much. If you have no visible problems, a gentle loosening of the roots and a light prune to remove any poorly positioned branches is all you need to do.
Regarding the ant problem, I tried all I could to make the bushes more healthy but I couldn’t seem to stop the voracious ants. Not only were they farming aphids and scale on the tip of each stem, but they got to the flowers & stole the pollen, which meant that they stopped the flowers setting fruit. This really annoyed me! I now sit each blueberry pot in a large 44cm wide (17″) saucer of water to stop the ants, and this simple barrier system works- see pic above. The water requires regular monitoring & changing like everything in the garden, but it’s the best solution I’ve found so far.