Jun 22, When to Prune Forsythia. The best time for trimming forsythia is in the spring after the blooms fade. Pruning forsythia in late summer or fall will reduce the number of flowers in the spring since these shrubs bloom on old wood and set their flower buds soon after new growth appears. The best time to trim your forsythia to keep its size or shape is right after it finishes blooming which is in the spring time.
Always remember to prune a shrub back for enough so that when it grows after a few months it will be the actual size you want. For example, if you want the forsythia to be 48 inches tall you will want to make you cuts inches below that so that. Prune these spring flowering shrubs soon after they have bloomed. Top prune the plant to improve the shape and reduce its size, but be careful not to remove more than 30% of the top growth.
Some summer pruning can also be done on particularly vigorous plants, but. Jun 01, For the standard forsythia (I'm not talking about the new varieties, but the old ones already growing when you move in, for instance), pruning comes in two kinds.
The first is renewal pruning, where less than a third of the canes or branches are removed. This might be done every three or four years or as needed.
Jan 03, For rejuvenation pruning or if you’re trying to reduce the overall size of the shrub, it’s best to make your pruning cuts in late winter or early spring when the forsythia is still dormant. Yes, this will sacrifice some of the spring-time blooms.