The Q&A Archives: Cutting back hydrangea; cutting back wiegalia

Question: I have several hydrangea that have taken off in their second season in the ground and have become quite large and articulate with each other. Is it appropriate to cut them back? If so, what is the best time to do so. The wiegalia is also getting big and the question is just about the same. Cut back/when?

Answer: As a general rule, when planting shrubs it is a good idea to check the mature size for the variety you are growing and space accordingly -- it can really be shocking how big they can grow in four or five years! A slight overlapping at the branch tips will not be harmful, but if they are really crowded you probably should do something. Pruning for size when they are planted way too close together is not practical in the long run. You will be spending a lot of time on maintenance, the blooming performance will be reduced, and the shrubs' natural shape will be destroyed.

When to prune hydrangeas depends on what kind of hydrangea you have. The commonly grown Hydrangea macrophylla should be pruned in summer right after it blooms, or you can head it back partway in the spring. Do not prune it back hard in the spring because these plants bloom on buds on wood that grew the year before. If they are way too large, and I suspect this is the case since they are crowding already and should grow even larger next year and after that when fully established, you may want to consider removing some to make space for the rest. Since they have only been in the ground for two years and are relatively shallow rooted you could transplant relatively easily next spring. Keep in mind that the rootball will be quite a bit larger than it was when you planted them, and when transplanting you want to take as much of the root system as possible.

Weigela blooms on old wood also, so do not prune it until right after it blooms in the spring. At that time you can thin it and remove some of the oldest and longest branches. These shrubs do not reach their full size until about year four or five, so if they are already crowding then you again need to (re)move them rather than try to prune them to fit. These are deep rooted so keep that in mind if you try to transplant. Late winter to early spring, as soon as the ground is thawed and before the buds begin to swell would be a good time to do that.

Good luck with your shrubs!

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