Browning foliage on a towering redwood tree, whether it is the Coast Redwood (Sequoia sempervirens) or the Giant Sequoia (Sequoiadendron giganteum), can be alarming. These conifers are known for their immense size and longevity, but they are susceptible to environmental or biological pressures that cause discoloration. A redwood’s natural health is defined by its deep green color. Any significant shift toward brown or yellow suggests the tree is under stress. Distinguishing between a normal biological process and a serious health issue requires careful observation of the browning pattern.
The Difference Between Normal Shedding and Distress
Redwoods are evergreen trees, but they still perform an annual “exchange of foliage” that can resemble distress. This normal process occurs when the tree sheds its oldest, least efficient needles, typically in late summer or early fall. The browning is concentrated on the interior of the tree, closer to the trunk and on older growth, while new growth remains green.
The shedding is often dramatic because redwoods are “cladoptosic,” meaning the tree drops entire short shoots or branchlets. These brown sprigs accumulate on lower branches, creating an exaggerated appearance of widespread browning that is benign. In contrast, distress browning usually begins at the tips of the branches or affects entire sections of the canopy rapidly, signaling a failure to transport water or nutrients.
Environmental Stressors That Cause Browning
The most frequent causes of unhealthy browning are non-biological, with insufficient water being a primary trigger for redwoods planted outside their native foggy habitat. When a redwood experiences drought stress, it conserves water by sacrificing the foliage farthest from the trunk. This results in brown needles that often start at the branch tips or the lower canopy, reflecting the tree’s reaction to a lack of deep, consistent moisture.
A tree can exhibit drought-like symptoms even when the soil is saturated, caused by poor drainage or “wet feet.” Excess moisture limits oxygen availability to the roots, which can lead to root rot diseases like Phytophthora or Armillaria, preventing effective water absorption. Redwoods are also sensitive to soil chemistry; high concentrations of salts (from de-icing agents or recycled irrigation water) can cause toxicity that manifests as scorched or brown foliage. Planting in heavy, compacted soil or in locations exposed to intense sun can also stress the tree, leading to browning and dieback.
Pests and Fungal Infections
If environmental factors are ruled out, browning may be caused by biological agents that attack the tree’s tissues. Fungal diseases often cause localized or random browning across the canopy, a symptom known as “flagging.” One common pathogen is Botryosphaeria canker, which causes branches to turn brown and die.
These cankers are localized lesions that girdle the branch, blocking the flow of water and nutrients, and often appear on trees weakened by drought. Insects also contribute to browning by disrupting the vascular system or feeding on the foliage.
The Redwood bark beetle (Phloeosinus spp.) bores into the bark, creating tunnels that interfere with the movement of water and nutrients, which leads to branch dieback. Smaller insects like scale, mealybugs, and spider mites are sap-suckers that cause needles to yellow, bronze, or brown over time. The presence of tiny holes, sawdust-like material (frass), or sticky honeydew can help distinguish a pest problem from an environmental one.
Steps for Diagnosis and Recovery
The first step in addressing browning is a thorough inspection to determine the pattern and location of the discoloration. If the browning is confined to the old, inner foliage during late summer, the tree is likely undergoing normal shedding and requires no intervention. For any other pattern, the focus must shift to cultural care.
Assess the soil moisture by digging a small hole or using a soil probe 12 to 18 inches deep near the canopy edge. If the soil is dry, deep, slow watering is necessary to alleviate drought stress, ensuring the water soaks in. If the soil is muddy or constantly saturated, improving drainage or modifying the irrigation schedule is required to prevent root rot.
Avoid applying fertilizer to a stressed tree, as the added salts can worsen the condition and interfere with water uptake. If the browning is rapid, covers more than 30% of the canopy, or is accompanied by signs of cankers or significant insect activity, consulting a certified arborist is the most reliable path to accurate diagnosis and specialized treatment.