May 1, 2002
Woodbury Bulletin
Betsy Halden

Forsythia signals spring

Flowering forsythia is one of the brightest signs of spring that we northern gardeners can enjoy in our landscapes. Our neighbors, Steve and Ann Bleyl, have forsythia bushes in full bloom this spring. Bright yellow flowers have covered the attractive shrubs. Hopefully, this eye catching display signals the start of the growing season. If you are fortunate enough to have a hardy forsythia such as “Northern Sun,” or other forsythia that withstands our zone 4 climate, you might wonder when you should prune it. Here is information about selecting a forsythia plant and tips for pruning it.

When selecting a forsythia for your landscape note the information on the tag about the hardiness of the flower buds. Our zone 4 winter temperatures can dip to –30 F. The forsythia bush, the roots and branches, may withstand colder temperatures, but the flower buds will not. Make sure you choose a cultivar that is hardy to –30 or 035 F.

Northern Sun forsythia was introduced by the University of Minnesota and is specifically recommended for landscape use in Minnesota. Plants have grown vigorously at the University of Minnesota Landscape Arboretum to an ultimate height and spread of 8-10 feet. The flower buds have proved hardy to – 30 F The shrub is adaptable to a wide range of soils and has no serious pests or diseases.

The time to prune forsythia is just after flowering. If you wait until summer or fall to prune it you will remove all the flower heads. If you prune immediately after flowering you will encourage new sprouts from the base of the plant. Many people prune their forsythia incorrectly and it leads to lack of light for the plant. If you take a hedge clipper and prune the forsythia plant like a hedge, shaping it into a ball, you will not get the best from your plant. This type of pruning results in a thick, dense mat of stems at the top of the plant.

If you look inside the “ball” you will find very few leaves, mostly woody stems. This is because the dense outside growth shades out the inside of the plant. No leaves or flowers is the result.

To rejuvenate a forsythia, prune out one third of the largest stems right at ground level. everywhere you make a cut new growth will result. next year prune out another one third of the oldest, thickest stems at ground level again. and the following year prune out the last one third old, thick stems. You will have a new plant with staggered growth. you are also allowing light to reach down into the plant which stimulates leaves and flower formation. When the new growth from the first year’s cut reaches the height you want, cut them out at ground level. This will always give you a staggered growth to the forsythia. It also give you a more natural look to your plant.

In addition to Northern Sun, gardeners in our area have reported good flowering with Meadowlark, New Hampshire Gold, Northern Gold, Sunrise and Bronxensis forsythia. To encourage free flowering, plant forsythia bushes in full sun.

Betsy Halden is a resident of Woodbury. She consulted Cornell Cooperative Extension and the University of Minnesota Extension Service materials when preparing this column. You can reach Betsy Halden at eahalden@comcast.net