Yes, forsythia cut back hard will grow right back. You can chop it down to 3 to 4 inches (7.6 to 10.2 centimeters) from the ground and it will bounce back strong. Few flowering shrubs handle this kind of severe pruning as well as forsythia does. It's one of the toughest plants you can own.
I did this exact thing to an overgrown forsythia in my side yard two springs ago. The previous owners had let it go wild for years and it had turned into a 10-foot tangled mess that swallowed the fence and blocked the gate. I grabbed my loppers and a hand saw and cut every single branch to stumps just a few inches above the soil. My neighbor thought I'd killed it. By August, fresh green shoots had pushed up 3 to 4 feet tall and the plant looked like a brand new shrub.
Wisconsin Extension backs up what I saw in my yard. They confirm that overgrown forsythia cut to 3 to 4 inches from ground level will regrow and start blooming again within two years. The first year focuses on putting out new branches and leaves. The second year, those branches mature enough to set flower buds and give you a fresh round of spring blooms. Forsythia rejuvenation pruning works because the roots send up fresh stems with tons of energy.
Timing matters when you're cutting forsythia to ground level. You have two good windows. The first is late winter before new growth starts, which is the approach most experts recommend. The second is right after flowering ends in spring, which lets you enjoy one last bloom display before the reset. Avoid hard pruning in summer or fall since the plant needs a full growing season to put out enough new wood before winter arrives.
Not sure if your bush needs this treatment? Look for these signs that your overgrown forsythia needs a full reset. Dead branches in the center, blooms only at the tips, or a tangled bird's nest shape all call for hard pruning. A few cosmetic cuts won't fix deep structural problems that built up over many years.
After you make the cut, help your forsythia recover fast. Water the root zone well through the first growing season. Spread 2 to 3 inches (5.1 to 7.6 centimeters) of bark mulch around the base. This holds moisture in and keeps weeds from fighting with the new shoots. You can skip fertilizer since the roots have plenty of stored energy to fuel the regrowth on their own.
The best part of forsythia rejuvenation pruning is the fresh start it gives you. Those new branches grow in a clean, open pattern instead of the dense tangle you cut away. You get a better-shaped shrub with stronger blooms and the chance to maintain it properly going forward. One hard cut now saves you years of fighting an unruly bush that refuses to look good no matter how much you trim it.
Read the full article: Forsythia Bush: Complete Growing Guide
