At what winter temperatures are the fruit buds of northern highbush blueberries damaged?
It depends by variety some can handle colder temperatures. I generally worry when the temperature drops below -10F but we do not see severe damage until the temperatures get into the -15 to -20 range. You can go out and collect some buds and let them sit for a day or two and then carefully cut across the buds and look for black or brown spots which would indicate a dead flower. Usually not all flowers are killed. Last year when we got down to around -20 four times we had significant injury which did not show up until growth and bloom when the number of flower buds looked normal, but there were very few leaf buds.