How can I bring my Arborvitae back to good health?

June 14, 2022 Ask the Expert, Managing Insect, Diseases, and Animal Pests

Question:

My Arborvitae has some brown branches on one side. What can I do to stop the spread and bring it back to health? It was transplanted last August and wrapped in burlap over the winter.

Answer:

Liz Stanley, Horticulture Community Education Assistant

It looks like an environmental problem rather than a pest or disease issue.

Some branch dieback is pretty common on arborvitae that are stressed from being recently planted or transplanted. Other stress factors include desiccation from winter wind, sudden swings in winter air temperatures, extreme changes in soil moisture, abrasion from ice, snow or plant wraps, shearing, overly dense branch structure, root damage from too much moisture, or too much salt (from roads, driveways or fertilizers).

Here are some things you can do to help the plant grow roots first, and eventually more top growth:

– Hold off on fertilizer, since they’re salts. (Most trees and shrubs don’t need added fertility if they’re planted well.)

– Avoid fertilizing after mid summer. Fertilizing late keeps the plant from slowly hardening off before winter.

– Hold off on acidifying the soil. Even though Arborvitae are conifers, they prefer a moderately alkaline soil with a pH between 6.5 – 8.

– Water deeply during dry spells but allow the soil to become almost dry between watering to prevent root rot.

– Remove any dead branches or branchlets, making a clean cut with bypass pruners.

– Look inside the plant. Many shrubs (including arborvitae) have very crowded interiors. This can prohibit air circulation inside the plant. Remove any dead, crossing or broken branches, branchlets or needles, stepping back as you work to keep the plant symmetrical.

Here are two resources about woody plants:

Selecting, Planting and Caring for Trees & Shrubs in the Maine Landscape.

Pruning Woody Landscape Plants

One of the best things about Thuja occidentalis is how much wildlife they support. They’re a magnet for birds that like dense cover – cat birds, song sparrows, chickadees, cardinals and Carolina wrens to name a few.