Actually forsythia like most flowering shrubs are not heavy feeders and should not need additional fertilizer each year. A newly planted shrub would benefit from an all-purpose plant food like Osmocote but once established shrubs do fine with just a light mulch of compost or wood chips. Are there pale leaves or some other indicator that your forsythia needs fertilizer? Would you like to send a photo of the shrub if you suspect it is sickly or not growing? Marianne Binetti