Boron in Irrigation Water: Assessing Risk to Soquel Redwoods

1.8 ppm Boron: Likely Not the Primary Issue

Boron toxicity in redwoods shows as tip burn on needles (yellowing starting at tips, progressing inward). Your description suggests different symptoms.

More Probable Cause: Overwatering

• Redwoods in clay soil + frequent irrigation = waterlogged roots.
• Symptoms: entire needles yellowing (not just tips), general decline.
• Clay holds water—drainage is critical.

Correct Watering Protocol

1. Check soil moisture 2-3″ down—water only when dry.
2. Apply 1 inch per week (measure with pan under sprinkler).
3. Once weekly maximum in absence of rain.
4. Mulch 3″ deep (keep off trunk) to stabilize moisture.

Boron Monitoring

• If tip burn appears despite correct watering, test soil/boron accumulation.
• Redwoods moderately sensitive; 1.8 ppm is borderline but often tolerated with good drainage.
• Gypsum applications can mitigate boron in some soils.

First Step

Reduce watering immediately to the protocol above. Most "sick" redwoods in landscapes suffer from kindness (overwatering), not boron.