How do you prune nineback shrubs?
Question:
I have five large ninebark shrubs. They are all close to six-feet tall with very thick growth. The branches on several of them have collapsed to the ground leaving the middle empty and unsightly. In the past this was apt to happen after a heavy rain and have always bounced back after a day or too. I’m thinking it might be time for a radical cut back of heavy trim. I would like your impression and information about when and how to cut these back/trim them back and any other suggestions you may offer.
Answer:
These shrubs and many other multi-stemmed shrubs like forsythia, red-twigged dogwood, some hydrangeas, etc. really benefit from pruning every other year or so. Here’s a good method for over-sized ninebark, which you can do in early spring or after bloom. Now is a great time to do this.
1. Remove any dead, crossing, or damaged wood. Cut stems as close to the base as possible.
2. If the area where the stems emerge is still crowded, remove old “bull wood”. These are usually the thickest stems, which are sometimes exfoliated and are too old to bloom.
3. Avoid heading cuts. If you need to shorten a stem, cut at a branchlet but avoid “topping” the plant.
Stand back and look as you work. The goal is to form an elegant “vase” shape when you’re done, or after the plant grows back. The plant will also have improved air circulation, which can prevent disease.
Another option is to do a complete renovation. This simply involves cutting the entire plant to about 6″ at the base. It will take two years for the plant to grow back to its natural vase shape. As the plant re-grows, thin some of the emerging stems so they’re not crowded. You’ll have a nice young looking shrub next year that will be more likely to flower.
I can’t tell how close these plants are to your house, but woody plants can be damaged by falling ice and snow. They can also keep moisture near your sills and siding, and damage curtain drains. A good rule of thumb for medium sized woody plants is 6-8′ or more from the foundation. (Herbaceous plants like peonies can usually be around 4′ from foundations.)
This publication has more detailed information and also instructive videos: Pruning Woody Landscape Plants. The video about pruning forsythia will apply well to ninebark.