Hydrangeas are one of the most popular garden shrubs in the uk they are loved for their reliability and the generous amounts of colour they offer and the length of flowering time hydrangea 39blue danube39 in an acidic soil will produce electric blue flowers and if planted in alkaline soil the flowers are pink with flowerheads up to 20cm 4083441 in diameter that will last well into autumn hydrangea 39blue danube39 grows well in sun or shade and can be planted in garden