Red leaves on blueberry
I have a small blueberry bush, and some of its leaves are turning red. The pictures are in the shade, but it gets 6 hours of sun a day, and it's watered three times a week. The red leaves don't seem to be a good thing, so I'd appreciate any advice as to what's happening and how I can help my blueberries!
Oakland County Michigan
Red leaves can be a sign of stress but don't tell a lot by themselves.
Cool weather can try leaves red especially early in the spring.
Intense sunlight can also cause red leaves especially in the young shoot tips as in your picture. Look to see if lower leaves have green in the shadows of upper leaves.
The picture of the bottoms of the leaves looks like you may have some powdery mildew. https://www.canr.msu.edu/uploads/files/Powdery%20mildew.pdf
I have a couple questions. What is your soil pH? Blueberries prefer an acid soil between 4.5 and 5.5. If the shoot tips were yellow early in the season and now turning red your problem is the soil pH is too high causing iron chlorosis.
Not enough nitrogen or the wrong kind of nitrogen can turn the leaves red. Blueberries and their relative rhododendrons and azaleas can only use the ammonium form of nitrogen so I recommend using a fertilizer formulated for these plants. Do not fertilize now. Fertilize in the spring. I recommend half early in the spring when the buds begin to swell and half after bloom as the leaves and shoots are growing. I do not recommend fertilizing after July. We do not want late shoot growth in the fall this reduces flower buds and reduces winter cold hardiness.
Mineral deficiencies can also cause red leaves and there is usually a pattern. Red margins of older lower leaves is usually caused by magnesium deficiency. Using a complete fertilzer will fix this
I see a lot of the older leaves that are bright red in the background of your photos and I am thinking this is probably multiple stresses as I have seen a lot of red leaves in commercial fields this year as growers a neglecting their fields this year. Are the plants getting plenty of water?