Gardeners learn patience because many plants will not be full of flowers until they are fully mature. Lilac and wisteria are two that take their time so even if you fertilize extra, the blooms will be sparse. Lilacs do like full sun, good air circulation and if your soil is naturally acid add a cup of lime around the roots this fall. Cut off the spent blooms from the few lilacs you do get to send more energy to the plant instead of seed production. I predict next year your older lilac will have more blooms and this number will just increase with maturity. Keep growing, Marianne Binetti