Boxwood Turning Brown? How to Tell the Causes Apart

Brown boxwood is most often winter injury, which shows on exposed sides and usually grows out by summer. Check the green stems before you relax, though: narrow black streaks plus fast leaf drop from the bottom up point to boxwood blight, a serious disease that spreads between plants. If you see that pattern, stop pruning, keep clippings out of the compost and contact your extension office.

Look-alike table

Look at where the browning sits, how fast it came on, whether the leaves stay on, and what the stems look like near the base.

Problem	Where and when	Leaves	Stems and roots	Response
Winter injury	Exposed, windward or sunny sides and branch tips; late winter to spring	Bronze to reddish brown	Stems mostly sound; some bark splits possible	Wait for new growth; screen and water next fall
Leafminer	Throughout the shrub; blisters from late summer to next spring	Blistered undersides, blotchy yellow to brown	Normal; larvae inside leaves	Prune back about a third; dispose of clippings
Phytophthora root rot	Whole plant, in wet or low spots	Green to yellow-green to straw or purplish brown; edges roll up and in	Dark wood 2 to 3 inches above the soil line; roots dark and few	Fix drainage; no chemical cure
Boxwood blight	Starts low and moves up; wet weather, often late summer and fall	Tan spots with dark borders, then rapid browning and leaf drop	Many narrow black streaks on green stems; roots not attacked	Contact extension; bag and remove if confirmed
Volutella blight	Branch tips, in spring	Straw-colored to tan; tend to stay on; pink spores in damp weather	Loose bark on dead branches	Prune out dead wood in dry weather; thin the plant
Dog damage	Low on the plant, at corners and along walks, at leg height	Brown and scorched in a low patch, without spots	Normal above the patch	Rinse with water; block access

Winter injury

This is the most common and least worrying cause. Cold, dry winds pull water from leaves faster than roots can replace it from frozen soil, and leaves turn from bronze to reddish brown. University of Maryland Extension warns that it can be confused with the early stages of root rot or Volutella blight.

Healthy plants usually recover, pushing out new leaves that hide the damage. Wait until new growth appears in spring before removing anything, then prune out what stayed dead. Our guide to winter burn on evergreens covers prevention in more detail.

For next winter:

Keep soil moist through fall, until the ground freezes.
Put a burlap screen about 18 inches from the plant on the windward side.
Don’t plant under roof eaves, where falling snow and ice can break branches.
Gently brush snow off before it weighs branches down.

Boxwood leafminer

The larvae of this small fly feed between the upper and lower leaf surfaces, leaving blistered, blotchy leaves from late summer through the following spring. Peel a blistered leaf apart and you should find the larvae inside. Early-spring damage is easily mistaken for winter injury, so check the undersides of the leaves.

University of Maryland Extension suggests pruning an infested boxwood back by about one-third to remove most of the larvae, then disposing of the clippings. That can eliminate the need for an insecticide. If you do spray, the timing window is narrow: in Maryland adults emerge in late April or early May, and shaking the branches shows when they’re flying. The date depends on your zone.

Root rot

Boxwoods are very sensitive to excess water. Phytophthora shows up as poor growth and off-color leaves whose edges roll upward and inward, with dark discolored wood at the stem base and loose lower bark. Older plantings can decline after drainage changes, for example when a downspout is moved or the grade changes.

There’s no chemical cure. Prevent it by avoiding poorly drained, compacted or low spots. Raised beds or regrading may be needed before you replant.

Boxwood blight

This is the one to take seriously. First come leaf spots, then rapid browning and leaf drop that starts on lower branches and moves upward. University of Maryland Extension identifies numerous narrow black streaks on green stems as the key difference from Volutella and Macrophoma. Symptoms often appear in late summer and fall, and long wet spells can bring them on at other times.

The fungus doesn’t attack roots, so a plant may push new leaves for a while, but repeated defoliation eventually kills it. Fungicides may suppress it in limited situations but don’t eradicate it.

Dog damage

A dog that regularly marks a shrub can scorch a low patch of foliage, typically on corners and beside walks. The telltale sign is location: the browning sits at leg height while the rest of the plant looks fine, and there are no spots or stem streaks. Rinsing the area with plenty of water and fencing off the corner are simple things to try. Dead foliage won’t recover, but the plant can regrow around it.

When to contact your extension office

Reach out if you see any of the following:

Black streaks on green stems
Leaf drop moving quickly upward from the bottom of the plant
A sudden decline in new boxwoods, or in plants near recently added ones
Browning you can’t match to anything above

Then do this:

Don’t move clippings around the garden or prune other boxwoods until you have an answer.
Send clear photos. Your local office may want a sample too. Virginia Tech advises double-bagging suspect samples, sealing each bag separately.
If blight is confirmed, bag and remove infected plants and fallen leaves. Do not compost them. See our guide to composting diseased plants.
Clean up after yourself. University of Maryland Extension advises laundering clothing, gloves and shoes and sanitizing tools. Our guide to garden tool care covers disinfecting blades.
Think before replanting. The fungus can survive in soil for years. Hollies and conifers are non-susceptible alternatives, and New Gen series, ‘Green Beauty’ and ‘Nana’ are cited as resistant boxwood examples, with lists that may change.

Pet safety

Boxwood is toxic to dogs, cats and horses, according to the ASPCA. Signs in dogs and cats include vomiting and diarrhea, and it can be serious in horses. Call your veterinarian or ASPCA Animal Poison Control at (888) 426-4435 if an animal has been chewing on it (a fee may apply).

Bottom line

Check location, speed and stems. Side-of-plant bronzing after winter usually recovers. Blisters mean leafminers. Soggy ground and dark stem bases mean root rot. Fast leaf drop from the bottom up, with black stem streaks, means it’s time to call your extension office before you touch anything else.

FAQ

Will brown boxwood turn green again?

Brown leaves won’t recover, but a shrub with live stems usually grows new leaves that hide them. Scratch a stem gently: green or pale tissue beneath means that stem is alive.

Should I prune brown boxwood right away?

Wait for new growth in spring unless you suspect blight. If you do suspect blight, hold off and get a diagnosis first, then clean your tools afterward.

Can I save a boxwood with blight?

Usually not over the long term. Removing infected plants is the standard advice, because fungicides only suppress the disease and need repeating through the growing season.