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Flowers, Fruits, and Frass

Prune properly, your forsythia and lilac shrubs will thank you

Yellow flowers on stems of forsythia, wood chip background

With the anticipation of spring and returning pops of color, you may find your forsythia and lilac shrubs are a bit lackluster from improper management.

The early-blooming and free-flowing forsythia, if managed like a hedge, portrays a strict military appearance, complete with a crew cut and almost flowerless display. Prompted by their massive sprawling nature, many gardeners and homeowners attempt to tame these beasts by midseason, relegating next season’s blooms to the compost pile. With proper pruning, both the timing and the technique, the stunning showcase of these spring bloomers can return next season. 

A gardener’s acceptance of the wild nature of forsythia or the mass of lilac is the first step to improved flowering. Often these plants are managed with the mindset of shaping coleus or petunia. With pruners in hand, the gardener mimics pinching back, attempting to shape these shrubs into a perfect mold. Sometimes this shaping is motivated by maintaining the large shrubs in a small space. If the shrub does not have the space to branch out, it should be replaced with a smaller shrub.  

How to Prune Forsythia and Lilacs

For the health of the plant, and to promote impressive floral display, forsythia and lilac branches should be pruned out at the base of the plant. It is best to remove 1/3 of the older branches every few years, within the two weeks following flowering.

For overgrown, unpruned shrubs, complete renewal pruning in one season by cutting back all branches within 6 inches of the ground. Regular pruning of lilacs is very important for disease management — a host of diseases can be prevented by increasing airflow with regular pruning and branch removal.  


How to Force Blooms

With proper placement and pruning, these show-stopping shrubs will provide an extended season of joyous flowers. Display the heralds of spring on your breakfast table, pre- and post-flowering by forcing blooms of forsythia or harvesting lilacs from your cutback. 

How to Force Bloom Forsythia

With buds formed the previous season, a late-winter forsythia has experienced the necessary cold treatment to erupt into flowers come warmer temperatures. With simple preparation, your warm kitchen will soon host sunny, yellow flowers! 

  1. Prune individual branches to the base of the plant. Select branches with plump round flowers buds rather than leaf buds. 

  1. Submerge cut ends in cool water (60°F) and cover with a plastic bag. Warmer water may cause flowers to distort.

  1. Remove bag when flower buds open in 7 to 10 days. Change water every 2 to 3 days. 

  1. Arrange flowers in your favorite vase. Continue to freshen water every couple days. 

How to Force Bloom Lilacs

When preparing for the great cutback of your lilac, prepare pruning tools and equipment for a harvest. Then, follow these simple steps to extend the lilacs blooming season in an arrangement, using your favorite vase. 

  1. Cut your flowers in the morning when they are full of water. 

  1. Condition blooms by removing foliage and submerging stems in a bucket of cool water for 1 hour.  

  1. After conditioning, recut stem ends and split stem ends vertically (1-inch-long split). 

  1. To ensure the longevity of your flowers, change the water daily and use floral food. 


Photo credit: Young forsythia; by Candice Hart, University of Illinois Extension


Kelly Allsup is a Horticulture Educator for University of Illinois Extension serving Livingston, McLean and Woodford Counties. She meets the educational needs of her community, including local chapters of Master Gardener and Master Naturalist volunteers, through expertise in home horticulture and entomology. Her passion for ecologically-friendly gardening and all things plants makes her a dynamic speaker on topics that range from beneficial insects, growing vegetables and fruits, to urban trees.