Why is my arborvitae turning brown? Northwest causes and fixes

Arborvitae turning brown: read the pattern first

Look at where the brown is, when it appeared and whether the branch tips are still green. Those three clues narrow it down before you spend anything on fertilizer or fungicide. WSU’s fall-shed guidance covers Northwest conifers in general, so the same first check applies to other evergreens turning brown, such as western redcedar.

Sources: WSU Extension FS056E and WSU Hortsense fact sheets; University of Minnesota Extension; OSU Extension hedge guide and Ask Extension; PNW Plant Disease and Insect Management Handbooks; Purdue Plant Doctor. Checked 2026-10-02.

Is it normal for arborvitae to turn brown in fall?

Yes, on the inside. WSU Extension Forestry’s fact sheet on Northwest conifers explains that evergreens shed their innermost foliage in fall, foliage that may be several years old, while keeping several years of newer growth. In western redcedar, whole branchlets color at once, a display called flagging; WSU puts redcedar’s foliage retention at two to five years.

University of Minnesota Extension describes the arborvitae version: older inner foliage turns golden brown to rust brown without spots, usually in September or October. WSU’s Hortsense ties heavy shedding to early fall after a dry summer and recommends no treatment.

Tip: Normal shed is even and inside; problem browning has a shape. If the newest growth at the branch tips is brown, or the brown is on one side or one plant, it is not the fall shed. For redcedars dying from the top down, see western redcedar dieback.

Summer drought and heat: scattered plants going brown

Summer is the Northwest’s dry season. Portland’s airport averages 0.51 inches of rain in July and 0.54 in August; Sea-Tac gets 1.57 inches across the two months, and Salem 0.64.

Drought damage is easy to misread because it arrives late. Retired OSU Extension horticulturist Neil Bell says even established arborvitae need water, that drought-stressed plants may not wilt right away, and that the damage shows as browning in fall. OSU’s guide adds the tell: winter browning usually affects all the foliage, while drought stress appears sporadically on individual trees in a hedge.

Heat can brown a hedge faster. During the June 2021 heat wave, Portland hit 108°F, 112°F and 116°F on June 26, 27 and 28, and Seattle reached 108°F on June 28 (NOAA Climate.gov). OSU researchers who studied the aftermath in Northwest forests found scorch appeared within days, sometimes hours, and was worst on south- and west-facing slopes and exposed edges. A hedge browned only on its sunny side after a heat spike fits that pattern.

Drought also opens the door to pests. WSU’s Hortsense notes spider mite outbreaks are often worse in dry, dusty conditions and that drought-stressed plants are more susceptible, and that flat-headed and shothole borers mostly attack plants already in decline.

Overwatering, poor drainage and root rot

Too much water browns arborvitae too. Asked about an eight-year-old planting that had been dying for two years, OSU Extension’s Amy Grotta answered that “often the culprit is poor drainage or overwatering,” which rots the roots; arborvitae need watering, she wrote, but no water should pond around them. OSU notes many Willamette Valley soils are clay-heavy, and Portland gets 23.90 inches of its 36.92-inch annual rain from November through March, 65% of the year’s total.

The PNW Plant Disease Management Handbook says many arborvitae samples sent to the OSU Plant Clinic come from poorly drained, wet sites where roots run short of oxygen. Above ground the plant discolors and eventually dies; below ground, roots are discolored under the bark. The handbook rates western redcedar the most resistant arborvitae to Phytophthora root rot and ‘Smaragd’, sold as Emerald Green, the most susceptible. How the two common hedge arborvitae compare is in Emerald Green vs Green Giant arborvitae.

1. Look after a heavy rainWater ponding around the base is the warning sign Grotta and the handbook both describe.
2. Test the drainageOSU’s infiltration fact sheet (EM 9214) explains filling a test hole to a marked depth and timing how fast the water drops.
3. Turn off the extra waterWSU’s Hortsense says to water deeply but infrequently and let the soil dry between waterings, and to avoid overhead or evening watering.
4. Check a rootGrotta notes disease can’t be confirmed without a root sample; the handbook’s observations come from samples sent to the OSU Plant Clinic.

Fungicides: the PNW handbook says plants with established root rot are most likely too far gone for chemical therapy; fungicides can protect healthy plants but don’t cure infected ones. For tip blight it lists copper sprays in spring and early summer during wet weather. If you spray, the label is the law: follow it for rate, timing and protective gear.

Brown tips and one-sided browning: winter, pests, dogs and deer

Winter injury browns foliage from the tip down in late winter or early spring, according to University of Minnesota Extension, usually on the exposed side or above the snow line, and the base often stays green. Some arborvitae cultivars also turn what OSU calls “a washed-out brown” in winter; Emerald Green typically does not.

Two pests mimic it. Cypress tip moth larvae mine one- and two-year-old shoot tips, which turn brown in late winter; WSU’s Hortsense rates western redcedar highly resistant and eastern arborvitae very susceptible, and the PNW Insect Management Handbook notes damage is usually limited to twig tips. Pestalotiopsis tip blight, a fungus, turns tips tan to brown with black fruiting bodies, mostly on plants already weakened by freeze injury, sunscald or poor watering, per the PNW handbook.

Low patches can be animals. Purdue’s Plant Doctor fact sheet describes urine damage as discolored or black foliage low on the plant, caused by salt and ammonia, and lists white-cedar (eastern arborvitae’s other common name, per NC State) among the species hit; it recommends rinsing the plant, soaking the ground and adding a barrier. Deer, OSU says, usually feed on the bottom 4 to 5 feet.

Care for arborvitae: watering, soaker hoses, mulch and fertilizer

How much and how often to water

For new plantings, OSU’s tree-planting bulletin says trees need the equivalent of 1 inch of rain a week from June through September and should be watered regularly for at least three years. For established hedges, OSU’s Neil Bell advises soaking every two to three weeks during dry spells. Clackamas County Master Gardeners, working with OSU Extension, note most absorbing roots sit in the top 12 to 18 inches of soil; WSU Spokane County Extension suggests checking the top 6 to 9 inches with a trowel before you water again.

Soaker hose for arborvitae: yes, with a check

Mulch for arborvitae

Portland Urban Forestry recommends 2 to 4 inches of wood or bark chips in a circle around the base, kept 3 inches off the trunk; Clackamas County Master Gardeners suggest a 3-inch layer to conserve moisture. Keep it out of the foliage: for plants with shoot-tip dieback, WSU’s Hortsense recommends clearing debris and bark dust from under the plants to improve air flow. Sources of chips are in free wood chips.

Arborvitae fertilizer: usually not the fix

OSU’s fertilizing fact sheet (FS 103) warns that reduced growth, leaf discoloration, or disease and insect problems are sometimes not due to nutrient deficiencies at all, and that a laboratory soil test shows whether phosphorus, potassium or minor elements are lacking. It also cautions that overfertilizing can leave damaging salts in the soil. OSU says new trees need no fertilizer at planting, and WSU links high-nitrogen fertilizer to spider mite outbreaks. More in fertilizing trees.

Will brown arborvitae grow back, or should you replace it?

Brown foliage does not turn green again, and bare wood does not resprout. OSU Extension’s guide says arborvitae do not produce new growth if cut back to bare stems, which is why a hole in the interior of an old hedge stays a hole. What can come back is a plant with live green tissue left: Bell says that if you prune out the damaged tissue and water the next summer, drought-hit plants may recover.

Western redcedar comes with its own caution: WSU forest health researchers link its dieback to warmer, drier summers, so a redcedar hedge needs summer water too. Its profile is on western redcedar.