Forsythia benefit from rejuvenation pruning. The younger thinner stems produce the most flowers and resist disease and pests, so cut the thickest oldest stems down to the base. If your shrub is overgrown, you can completely cut the entire plant down to the ground and the root system will regrow. It probably won’t bloom for several years, but it will be healthy and beautiful. Forsythia is not native to North America, so it would be even better if you replaced this plant with native vernal, witch

Tannerella forsythia - Alchetron, The Free Social Encyclopedia

Forsythia is an easy to care for shrub that comes back in the early days of spring each year. Find out how and were to plant it as well as some tips for transplanting and propagating it. https://thegardeningcook.com/planting-forsythia/ | The Gardening Cook

Planting forsythia! Here’s a good how-to video for planting all shrubs! 🐝💛 . #forsythia #athomeprojects #springgardens #pollinatorfriendly #balleksgardencenter | Ballek's Garden Center

Forsythia

Weeping Forsythia Bush Seeds for Planting (50 Seeds) - Forsythia suspensa - Stunning Yellow Blooms