Evergreens are valued for their year-round color, so the appearance of brown or reddish-brown needles often signals underlying distress. This discoloration is a symptom, frequently related to environmental factors, insect infestation, or poor planting conditions. Understanding the specific cause is the first step toward restoring the plant’s health and ensuring its longevity. Because these trees retain their foliage year-round, proactive care is the most effective strategy for maintaining their vibrant color.
Environmental Stress and Desiccation
The most frequent cause of widespread browning, often termed “winter burn” or desiccation, occurs when needles lose moisture faster than the roots can replace it. This is common in winter when wind and sun accelerate water loss while the surrounding soil is frozen solid. Since water in the root zone is locked up as ice, the plant cannot draw up moisture, leading to severe dehydration of the needles, particularly on the windward side.
Preventing moisture loss begins with deep watering into the late fall, continuing until the ground freezes completely. Saturating the soil provides a reservoir of hydration the roots can access during brief winter thaws. Applying three to four inches of organic mulch around the base helps insulate the soil and maintain a stable root temperature. Keep the mulch ring away from the trunk to prevent moisture buildup and potential rot.
Physical barriers can shield susceptible evergreens from the drying effects of harsh winter winds and intense sunlight. Erecting a simple windbreak, such as a burlap screen facing prevailing winds, reduces the rate of moisture evaporation. For broadleaf evergreens like boxwood or rhododendron, an anti-desiccant spray can be applied in late fall to create a thin, waxy coating on the foliage. This protective layer slows the transpiration rate, but it must be applied on a mild, dry day when temperatures are above 40 degrees Fahrenheit to properly set.
Pests and Pathogens
Browning can indicate feeding insects or fungal diseases attacking the plant’s foliage. Diagnosing the specific organism is important because treatments for pests and pathogens differ significantly.
Spider mites, particularly the spruce spider mite, thrive in cooler weather and feed by piercing needles to suck out sap. This feeding causes fine yellow or gray stippling, which eventually bronzes and turns brown, often starting on the older, inner foliage. To check for mites, shake an affected branch over a white sheet of paper and look for tiny, slow-moving specks. Initial treatment involves a strong stream of water to physically dislodge the mites, followed by an application of horticultural oil.
Fungal diseases like needle cast cause browning concentrated on the inner, older needles, leaving the new growth at the tips temporarily green. Pathogens, such as Rhizosphaera on spruce, infect new needles, but symptoms may not appear until the following spring or winter. Managing needle cast involves removing and disposing of infected fallen needles and branches to reduce fungal spores. Fungicides can be applied when new needles emerge in the spring to protect susceptible growth from initial infection.
Soil Health and Planting Practices
The long-term health and color of an evergreen are determined by the foundational conditions of its root environment. Poor planting practices or inadequate soil structure can lead to chronic stress that manifests as browning.
Planting an evergreen too deeply is a common error that suffocates the roots and leads to decline. The root flare, where the trunk widens at the base, should be visible just above the soil line after planting. If the soil has poor drainage, roots sit in waterlogged conditions, starving them of oxygen and causing root rot. Improving drainage before planting is necessary, ensuring the soil texture allows for proper gas exchange.
Chemical damage from sources like road salt runoff or pet waste can cause localized browning. Road salt is absorbed by the roots or damages the foliage upon contact, leading to browning, primarily on the side facing the street. Placing a temporary barrier between the plant and the salted area during winter can help. Thoroughly washing the foliage with fresh water in the early spring removes accumulated salt residue.