QuestionsHow to growTrees and ShrubsFeedingHydrangea slow growing 0 Vote Up Vote Down David Malone asked 12 years ago I have hydrangeas and they are very slow i have them sown about 3 yrs and am only getting 5 to 10 flower heads the spread is only about 2ft in that time what can i do to bring them on quicker 1 Answers 0 Vote Up Vote Down Gerry Daly Staff answered 5 years ago The plants may be a bit hungry. Feed with tree and shrub fertilizer or general fertiliser in spring or early summer each year.