dclegg,

Blueberries do best with frequent applications of fertilizer, monthly or even weekly. You did not say if they are in ground or in pots?

BB love ammonium sulfate, it is 21-0-0 so just nitrogen but that is what they need most if they are in ground you can give that for months before a more balanced fertilizer is given, 1 tsp per gallon, less if they are in pots. Make sure they are never dry when the AS is applied. At Lowes or HD your best bet is Miracle grow Camellia formula used per instructions.

If you have a helena chemical near you they have a dry fertilizer a 12-4-8 with all the components coming from a acid source, they call it a Blueberry special. Just make sure whatever fertilizer you use on them does not contain muriate of potash. The nitrogen should not be from a nitrate source.