How to Prune Forsythia: Timing, Thinning and Renewal

Prune forsythia immediately after it flowers, and thin the oldest stems at ground level rather than shearing the whole shrub. Iowa State says forsythias bloom only on the previous year’s growth (old wood), and that pruning anytime from mid-summer until just before bloom will reduce flowering in spring. Clemson gives the reason for spring timing: pruning after flowering lets the buds for next year develop in the fall. This guide sits under our forsythia care guide.

Why timing matters

The two sources agree on the window: after the yellow flowers fade, and before mid-summer. In Iowa that bloom is typically early to mid-April (Iowa State).

How much to remove

For mature shrubs, Iowa State says it is best to remove one-fourth to one-third of the oldest (largest) stems at ground level every other year.

Which cuts to make

Clemson says pruning should not be a shearing process, but a thinning out of the older branches at the base of the plant, allowing the more vigorous branches to take over. Clemson also says forsythias are often sheared to make a formal hedge or to reduce the size of the plant, but this detracts from the graceful habit of growth.

1. Wait until the flowers fade. Prune immediately after flowering (Iowa State).
2. Find the oldest, largest stems. These are the ones to remove (Iowa State).
3. Cut them at ground level. One-fourth to one-third of them, every other year (Iowa State).
4. Let the vigorous stems take over. Clemson’s goal for thinning at the base.
5. Do not shear. Shearing detracts from the natural habit (Clemson).

Renewing an old, neglected shrub

Iowa State says old, neglected forsythias can be rejuvenated by pruning the shrubs back to within 4 to 6 inches of the ground in late winter or early spring. The shrubs will grow back quickly and should begin blooming again in 1 or 2 years.

Mistakes to avoid

For sun, size and cultivars, see the forsythia care guide. The same prune-after-bloom rule applies to lilac.