I have three forsythias that have gone a bit crazy! wanting to trim them but they just seem to spread out wider and wider when i cull branches out. and where ever a branch touches the soil they are rooting! Can I cut them right back and let them start over or are they beyond redemption? They bloom lovely in the spring but for the rest of the season they are rather over powering in their location!
You give a perfect description of the traditional forsythia. Every year, you should remove 1/3 of the branches to the ground, starting with the oldest ones. Over time, this contains the spreading nature and stimulates growth of young canes that flower the next year. You can cut it down completely although it is a tad late to be doing that sort of rejuvenation pruning. Usually it is done during late winter or right after it flowers. If you go ahead, new branches may not have time to form flower buds for next spring. There are now some hybrids that sprawl less and are not as tall. But spring pruning of old wood is an annual chore for all of them.