Why Are The Berries On My Four 5 Year Old Blueberries Bright Red
They are in large pots (60 cm) and have cropped poorly but blue for the last 5 years. Ericaceous soil and feed and rainwater. Weird but the blackbirds won't touch them this year. All berries are scarlet. Help
Certified GKH Gardening Expert
Hm. This is usually caused by a pH issue, but If you are using acidic soil and fertilizers, then I would check to make sure that the mix does not contain any nitrates. This could definitely be ammonium nitrate damage.
Blueberries need, not only, acidic soil but they also need ammonium sulfate, rather than ammonium nitrate as a nitrogen source.
Be sure that you are feeding with a blueberry fertilizer, or one that does not contain nitrates.
These articles will help: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-ph-plants.htm