Asked August 1, 2017, 10:11 PM EDT

We have shrubs that are in a rocked area. When we purchased them over 15 years ago, we were told they would not need to be trimmed and they would stay about 3 feet in diameter. As you can see, they are very large and cover a chuck of the flower garden. We have trimmed them once about 2 years ago. Can we trim these way back? Do they need to be replaced? Any suggestions to cut them back so they don't cover the garden? Thank you.

Ramsey County Minnesota

1 Response

Arborvitae (Thuja) The needles of arborvitae are flat, frond-like fans. Cones are distinct, half-inch clusters. Arborvitae comes in many different forms and sizes that should be maintained when pruning. Arborvitae will withstand heavy pruning and shearing because new branches develop from concealed buds in the branch crotches. Prune in early spring or mid-summer.

  • When heavy pruning is necessary, prune before new growth begins in early spring so that new growth conceals pruning cuts.
  • To lower the height (no more than 20 percent) of a plant, cut back to a lower branch crotch, making cuts only into live wood. To regain the natural shape of the plant, balance lower limbs by lightly pruning branch tips.
  • Older arborvitae growing in shade will develop a dead zone that is incapable of regenerating new growth. Do not prune into this area.
  • Oriental arborvitae (Thuja orientalis) is slow growing and responds best to shearing new growth only. Ref. Morton Arboretum
Follow the directions carefully or risk very ugly shrubs. I have seen many more mistakes than successes. Topping them in one stroke makes an ugly shrub.