The forsythias bloomed later than usual this year, sometimes overlapping with the earliest lilacs–but they did bloom. If yours didn’t bloom, here are some things to consider:
The flowers for forsythia are set the year before they bloom. That means if you prune your shrub too late in the season, you will cut off the wood that has the flowers growing on it. The standard advice is to prune forsythia about two weeks after it’s done blooming. Don’t shear it like a hedge, but cut entire branches down to the ground. I prefer to prune my forsythia in very early spring, because it’s a lot easier to see what to prune. Those branches won’t bloom outdoors, but I force them indoors for a little early spring sunshine.
Too Much Shade
Forsythia needs full sun. You probably read the tag before you planted it, and planted it in full sun–or what you thought was full sun. It could be you planted it before the trees leafed out, and didn’t realize a tree would shade it. Perhaps you planted it on the sunny side of the house, never realizing it was in shade all afternoon. Or maybe you really truly did plant it in full sun, but several years later, other trees and shrubs have grown and now shade it. Take a good hard look at your forsythia’s location at several different times during the day to determine if this is the problem.
Too Much Neglect
If you don’t do any pruning to your forsythia for several years–like I did–it can start to shade itself out. You need to renovate the shrub. Even more detailed directions for pruning forsythia can be found here.
Too Darn Cold
The fact that forsythia blooms on old wood is one reason why some northern gardeners get little or no bloom on their shrubs. Those delicate little buds don’t always make it through the winter. I was sure glad I found this out before I plunked bought the forsythia of my childhood, ‘Lynwood Gold.’ ‘Lynwood Gold’ is rated hardy to Zone 4, but it’s only bud-hardy to Zone 5–in a good year.
I grow ‘Meadowlark,’ which is supposedly bud hardy to -35F (-37C). (That makes it hardy to USDA Zone 3.) Fortunately, I haven’t had to personally verify this. You can also look for ‘Northern Gold, ‘Northern Sun,’ ‘Vermont Sun,’ ‘New Hampshire Gold,’ or ‘Ottawa,’ which are all supposed to be bud-hardy to USDA Zone 4.
One day I would like to grow all these bud-hardy forsythia side by side to see what the differences are.