When you think about hydrangeas you may picture big, pom-pom-shaped clusters of flowers in blue or pink. Those are mophead hydrangeas. Lacecap hydrangea, on the other hand, have flat clusters of flowers. They also bloom in pink and blue. Pruning the lacecap hydrangea should be done each June or July, right before the plant produces buds. Lacecap hydrangeas bloom on what is known as "old wood." This describes stems that were produced in the season prior to the current one. The buds will produce on these stems beginning in August, so if you prune the bush after July you run the risk off cutting off what will be the current season's flowers.
Remove all dead stems by cutting them off at their point of origin.
Cut the lacecap hydrangea bush down one-third only if it is at least 5 years old. Prune one-third of all stems to the ground. According to the experts at the website Hydrangeas Hydrangeas, this will revitalize the plant. Choose stems that are not in keeping with the shape you desire, or just uniformly cut the plant back by one-third.
Rake the flower bed to remove all mulch and pruning debris, bag it and dispose of it.
Water the lacecap hydrangea plant until the soil is saturated and the water puddles at the base of the plant.
Apply a fresh, 3-inch layer of mulch, 2 inches away from the base of the bush, spread out to the dripline (the tips of the widest branches).