The most common species of Hydrangea is H.macrophylla and these are broadly divided into 'Lace-caps' and 'Mop-heads'. They are both good sea-side plants in Ireland, thriving in acidic soil where the pink forms will often exhibit fine blue colouring. They are grown in tubs or will do well in semi-shade, where they reach 2m x 2m. Although long flowering in summer, newer cultivars are also 'repeat' flowering, extending the season further. Pink Hydrangeas in tubs or in limestone soils can be turned blue by the application of aluminium sulphate. 'Mop-head' Hydrangea have flower heads that are made up of all sterile florets, e.g. they have no sexual parts in the flower but are modified to be showy. Thus they form the typical mop (rounded) head of sterile florets.