How to prune border forsythia

Immediately after flowering (early to mid-spring). Cut up to one-third of the oldest, darkest stems to the base. Shorten remaining flowered stems to a strong sideshoot. Avoid clipping the whole plant into a hedge shape — this reduces flowering.

Annually after flowering. Border Forsythia must be pruned right after flowering — it sets next year's buds on new wood produced over summer. Wait too long and you cut off next spring's display. Remove about one-third of the oldest stems at ground level each year to maintain an open, arching shape and keep flowers coming on young growth.

Cut up to one-third of the oldest, darkest stems to the base. Shorten remaining flowered stems to a strong sideshoot. Avoid clipping the whole plant into a hedge shape — this reduces flowering.