It is obvious why spiraea x cinerea 39grefsheim39 has been awarded the coveted rhs agm33 this deciduous shrub is simply amazing in late april and early may when the 39bridal wreath39 spirea is covered in a mass of white flowers they are set off against a backdrop of grey45green leaves and the stems adopt a graceful arching habit easy to grow this plant makes a wonderful specimen and it39s great for biodiversity too as the flowers attract beneficial insects and the stem