Forsythia is a classic, old-fashioned garden shrub, and its sunny yellow flowers are a welcome herald of spring.
Early, profuse bloom entices us to include this plant in our gardens and landscapes. Slender, wiry, naked branches are covered with flowers and, as they fade, shiny green leaves fill in to clothe the stems until autumn.
In overall shape, the shrub is something of a wild-child, with a naturally unkempt form. Plants are generally either irregular and upright to rounded, or loosely fountain-shaped, with upright arching branches that reach up then out and down to touch the ground.
We love their spring display, but may struggle with how to keep them looking nice for the rest of the season.
They are often clipped into hedges or trimmed into balls or cubes to give them a more tidy form. They adapt surprisingly well to this treatment and will continue to provide an excellent spring show as long as they are clipped early in the season. Flower buds are formed in the summer, so later season pruning will remove the following spring’s display.
The school of good shrub pruning teaches us to keep plants slightly wider at the base than the top to prevent the plant from shading itself. Shaded lower stems eventually stop producing leaves, creating a leafy tabletop with a twiggy bottom.
Formal shearing can be challenging to maintain, thanks to forsythia’s exuberant growth. You may opt for a more natural form to reduce pruning, which also looks good in an informal landscape or blended into the blowsy style of cottage gardens with mixed perennials, shrubs and annuals.
For the upright forms, give them a post-flowering trim to remove any wild stems that disturb the overall shape. Mounded forms benefit from the same, clipping any stems that shoot straight up or are more vigorous than the rest of the plant. When branches grow long enough to touch the ground, clip them back, or the grounded portion will form roots and start a new plant.
Keep in mind that each cut encourages the branch to become fuller at that spot — whether you’re lightly trimming or cutting back hard to reduce the plant’s size.
Its form will appear more natural when cuts are made deeper into the plant, and at varying lengths.
Flower buds on common forsythias can be killed when temperatures dip to minus 10 degrees, resulting in erratic or spotty blooming in spring. Plants themselves are reliably hardy to minus 30, but since the flowers are the main attraction, this problem can be frustrating. A harsh winter with good snow cover creates a strange looking spring scene when twiggy shrubs bloom on only the lower portion that was protected by the snow.
Fortunately, hybridizers in Canada, South Dakota and Maine have developed varieties of Forsythia that are flower-bud hardy to colder temperatures. Meadowlark is considered the most dependable, with profuse flowers even after winters 35 degrees below zero. Shrubs grow 6 to 9 feet tall and have the typical unkempt shape that will benefit from some pruning.
Northern Gold has richly colored flowers hardy to at least minus 30, on 6- to 8-foot tall shrubs with an upright form. Northern Sun is similarly hardy, slightly larger at six to nine feet, and has softer, clear yellow blooms.
Low-growing selections like Gold Tide are not in the extra-bud-hardy group, but with a height of only 18 to 30 inches, plants are rarely exposed to damaging winds. Variegated foliage forms provide season-long beauty, but tend to be sparse-blooming regardless of the winter.
Choose a variety that fits your garden’s style.