Experts and BHG readers answer.
forsythia is not blooming
"The time to cut forsythia back is right after it blooms. Wait much longer than that and you will remove flowerbuds.
Forsythia respond well to drastic pruning. You can cut them down to about 18 inches and let them regrow from there. Other possibilities for the lack of bloom include heavy shade.
Luke Miller, editor
Garden Ideas & Outdoor Living magazine"