Dawn Redwood (Metasequoia) Bonsai Tree Leaves Turning Brown

When the leaves (needles) of a redwood bonsai tree start turning brown and dying, it can be concerning, as redwoods are typically hardy trees. Several factors might be causing this issue, and addressing it promptly can help revive your bonsai. Here are some common causes and solutions:

1. Underwatering

• Cause: Redwoods require a consistently moist environment, and drying out even briefly can stress them, causing browning needles.
• Solution: Check the soil daily, especially during warm or dry weather, to ensure it stays consistently moist but not soggy. Water thoroughly until water drains from the bottom of the pot, and avoid allowing the soil to dry out completely.

2. Overwatering or Poor Drainage

• Cause: While redwoods love moisture, waterlogged roots can suffocate and begin to rot, leading to browning and needle drop.
• Solution: Use well-draining soil and ensure the pot has drainage holes. Only water when the top of the soil feels slightly dry. If the soil retains too much water, consider repotting with a bonsai-specific mix that retains moisture but drains well.

3. Low Humidity

• Cause: Redwoods thrive in humid environments, and low indoor humidity (often under 40%) can cause leaf browning, especially at the edges.
• Solution: Increase humidity by placing the bonsai on a humidity tray (a shallow tray with pebbles and water) or misting the tree daily. Keep it away from dry air sources, such as heaters or air conditioners.

4. Sunlight and Heat Stress

• Cause: Redwoods need bright, indirect light. Too much direct, intense sunlight, especially in the afternoon, can scorch the leaves, turning them brown.
• Solution: Place the bonsai where it gets morning sunlight or bright, indirect light. If outdoors, position it in partial shade to avoid intense afternoon sun.

5. Nutrient Deficiency

• Cause: Lack of essential nutrients, especially nitrogen, can lead to poor growth and browning.
• Solution: Feed the tree with a balanced, diluted bonsai fertilizer during the growing season, following package instructions. Be cautious with feeding in winter, as redwoods require less fertilizer when dormant.

6. Pests or Disease

• Cause: Spider mites, aphids, and fungal diseases can attack redwoods, leading to browning leaves.
• Solution: Inspect the needles and branches for signs of pests or fungus (e.g., webbing, tiny insects, or powdery spots). Treat with insecticidal soap or a fungicide as needed, and ensure good air circulation around the bonsai to prevent fungal growth.

7. Seasonal Needle Drop

• Cause: Some browning and shedding are natural in late fall and early winter as redwoods prepare for dormancy.
• Solution: This is typically part of the tree's cycle, and as long as the browning is minimal, it’s normal. Remove any brown, dead needles to maintain appearance and improve airflow.

Summary

To revive your redwood bonsai, start with consistent watering and humidity adjustments, check for pests, and provide suitable light. With some attention, you should see new, healthy growth in the coming season.