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Coast redwoods (Sequoia sempervirens) turn brown in hot, dry weather when heat and limited water put more strain on their foliage and roots than the tree can manage. They are adapted to cool, moist conditions, so inland heat, low humidity, drying winds, and a lack of summer fog can all contribute. But brown needles do not automatically mean disease or that the tree is dying: older foliage inside the canopy normally browns and drops seasonally. The location, spread, and progression of the browning—and the condition of the soil—are better clues than color alone.
Why hot, dry weather stresses redwoods
Coast redwoods are native to cool, moist environments. In places that are hotter and drier, a tree may lose water from its foliage faster than roots can replace it. Low humidity, dry winds, a lack of summer fog, and hot soil can intensify that imbalance. Soil conditions matter too: compacted ground may restrict roots or prevent water from reaching them, while poorly drained soil can deprive roots of oxygen even when it seems there is plenty of water.
This helps explain why browning in an inland landscape may reflect a mismatch between the tree and its growing conditions rather than a single disease. A University of California Cooperative Extension account of ornamental redwoods in Bakersfield attributed much of the browning observed there to the local climate and soil, which differ from the cooler, more humid coastal and mountain settings redwoods are adapted to. That is a regional observation, not a diagnosis for every tree or location.
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Heat is not only a way of drying the soil. It can also affect the tree’s ability to function. A University of California, Davis news report published September 28, 2026, describes a study that followed coast-redwood responses over three summers in Mendocino County. During the summers of 2022 and 2024, when air temperatures topped 86°F, some leaves were nearly 20°F warmer than the air. In laboratory tests at temperatures up to 110°F, photosynthesis was reduced.
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These findings show that heat can impose a physiological burden; they do not establish a universal temperature at which redwoods will brown or die. Lily Klinek, the study’s lead author and a Ph.D. candidate in the UC Davis Department of Plant Sciences, said, “The leaves aren’t able to cool down,” and noted, “We don’t know what the upper temperature thresholds are for redwood photosynthesis and mortality.” The reported 110°F laboratory range is not a proven mortality threshold for trees outdoors.
Is brown foliage normal, or a sign of decline?
Redwoods naturally shed older foliage. UC Agriculture and Natural Resources guidance says older leaves toward the interior of the canopy can yellow, turn brown, and drop in late summer and early fall. Short twigs may brown and fall as well. If browning is limited to older inner foliage and there is healthy new growth at the ends of branches, that pattern is different from extensive, advancing dieback.
Widespread browning, drooping foliage, or a marked reduction in new growth deserves closer attention. In a regional ornamental-redwood report, heavy water stress was associated with discolored, drooping needles that died from the tips inward, reduced new needle flush, and discoloration across the canopy. These are signs to consider together, not a definitive diagnosis: drought, root trouble, pests, pathogens, or more than one stress can produce overlapping symptoms.
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Use pattern and progression as clues
- Where the browning starts: Older leaves in the inner canopy that brown and shed seasonally can be normal. Browning at branch tips, across the crown, or across much of the canopy is more concerning, particularly if it is spreading.
- Whether new growth appears: New growth at branch ends indicates those branches are still alive. Little or no new needle flush alongside expanding discoloration can signal continuing stress.
- How foliage changes: Drooping needles that discolor and die from the tips inward are consistent with significant water stress in the regional report, but do not identify its cause on their own.
- How quickly symptoms progress: A stable patch of inner-needle shedding differs from a crown that continues to lose live branches. Note the timing and take dated photographs from the same viewpoints to see whether the pattern changes.
- What is happening at the site: Soil moisture, drainage, irrigation coverage, compaction, nearby hardscape, competing plants, salinity, and recent heat or dry winds can help explain the pattern.
A dead or brown top is not enough by itself to conclude that the whole tree is dead. Look at the rest of the crown and whether live branches are producing new growth; extensive or progressive crown dieback, however, is a reason to seek an in-person assessment.
Could a disease or pest be causing the browning?
It is possible, but brown color alone cannot distinguish disease from environmental stress. Root pathogens, cankers, insects, and animal damage are among the other possible contributors. The order in which symptoms appear, the part of the tree affected, and the growing conditions are all relevant to diagnosis.
For example, UCANR’s Kern County discussion describes Cercospora blight as often beginning on lower branches and spreading outward under cool, wet conditions. The author cautioned that the observed Bakersfield pattern did not fit that explanation. This example is useful because it shows why a disease label should not be inferred just from browning; it is not a rule that can diagnose trees in other regions.
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Ask whether the pattern makes sense for the suspected cause and whether site conditions offer a simpler explanation. A local cooperative-extension office or an on-site certified arborist can assess details that photographs may miss, especially below ground. Photos alone cannot rule out root damage or pathogens.
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Start with the root area rather than spraying foliage or adding fertilizer. The goal is to understand whether water is reaching the absorbing roots, whether it drains, and whether other conditions are interfering.
- Map the browning. Note whether it is inner and seasonal, concentrated at tips or low branches, limited to one side, or spreading through the canopy. Look for drooping, dead twigs, and new growth at branch ends.
- Check soil moisture and penetration. Feel or inspect soil in several places across the root area, not just directly beside the trunk. A simple rod or dowel can help reveal whether water has penetrated below the surface; a specialized electronic meter is not required by the cited extension guidance.
- Check drainage as well as dryness. Observe whether water soaks in or remains standing, and whether the area stays waterlogged. Redwoods can be harmed by poorly aerated soil as well as by insufficient water, so extra irrigation is not automatically helpful.
- Look for barriers and competition. Hardscape, runoff, compacted soil, and nearby plants may affect how much water reaches roots. Avoid digging or otherwise disturbing roots while investigating.
- Review recent conditions. Record heat, dry winds, irrigation changes, and when browning began. A short history can help an extension specialist or arborist distinguish a seasonal pattern from continuing decline.
What to do during hot, dry weather
Water slowly and broadly when the root area is dry
If the root area is dry during hot, rainless weather, slow, deep watering spread across the root zone may help. A soaker hose is one option for applying water gradually and over a wider area. Check soil afterward to confirm the water has reached the root zone rather than running off or wetting only the surface. Adjust based on local conditions and drainage instead of following a calendar without checking the ground.
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One Ask Extension response for a redwood in the Willamette Valley suggested saturating the top 12–18 inches of soil about weekly until fall rains. That was advice for a particular tree and setting, not a universal schedule. Soil type, rainfall, temperature, tree size, and drainage vary; applying it everywhere could lead to waterlogged soil or unnecessary irrigation.
Use mulch carefully
Mulch can reduce soil-moisture loss. Spread it over the root area, but leave a gap around the trunk and do not pile it against the bark. Keep mulch from hiding the trunk flare or creating a persistently wet collar at the base of the tree.
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Avoid interventions that add another stress
- Do not compact the root area with vehicles, heavy equipment, or repeated foot traffic.
- Avoid root disturbance while checking soil or changing nearby landscaping.
- Do not increase irrigation blindly where soil drains poorly or remains wet.
- Do not assume fertilizer or fungicide will cure browning. A regional Kern County article says added nitrogen may encourage growth that masks older brown needles, but describes limited treatment options in that setting and reports no studies showing fungicide treatment effective for the suspected diseases it discusses. Those observations are regional guidance, not a general treatment prescription.
When to get a local assessment
Contact a local cooperative-extension office or a certified arborist who can inspect the tree on site if browning continues to spread, the crown is losing substantial live branches, or you cannot determine whether soil is dry, compacted, or poorly drained. Seek help sooner when the tree’s condition presents a safety concern. An on-site professional can examine the root area, site, and symptoms together; a photo alone may not reveal root injury or a pathogen.
There is no broadly applicable percentage for how many redwoods brown in hot weather, and the cited sources do not establish one temperature threshold for browning. The practical question is not simply whether any foliage is brown, but whether the pattern is seasonal or progressive and whether the tree’s site and water conditions can explain it.
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