University of Missouri Extension horticulture specialists said on Apr. 15 that reports are increasing across the state about browning in arborvitae, a popular landscape evergreen.
This issue is important for homeowners and landscapers because arborvitae is widely used for privacy screens and borders due to its rapid growth and low maintenance. Understanding the causes can help prevent further damage to these plants.
Debi Kelly, University of Missouri Extension field horticulturist, said drought stress beginning last fall may be responsible for the discoloration. Arborvitae requires consistent deep watering, especially when newly planted or during dry periods. Mulching can help retain soil moisture, and thorough watering should continue until the ground freezes each year. During winter thaws, watering is still recommended if possible.
Kelly also noted other potential problems: “If arborvitae needles brown and drop prematurely during hot summers—even with adequate watering—resulting in thin areas, spider mites may be the cause, especially when damage appears on the south or west side of the tree.” She added that yellowing and dropping of older inner needles is normal: “This is part of the natural life cycle of arborvitae…and is nothing to be alarmed about.” For optimal growth, she recommends planting in full sun with moist, well-drained soil and protecting from strong winds to avoid windburn.
Fertilization should not occur from late summer through winter; instead it should be done early in spring using high-nitrogen formulations such as 20-15-15 or 10-5-5. Damaged branches should be pruned in late spring when new growth appears. MU Extension horticulturist David Trinklein said: “Pruning arborvitae helps maintain the health, size, form and vigor of trees and shrubs in the landscape…Pruning can slow the spread of decay or disease by removing infected tissue and allowing the plant to seal, or compartmentalize, damage.”
Historically known as “tree of life,” arborvitae was used by early French explorers and Native Americans for medicinal purposes due to its vitamin C content. Its wood was also utilized in canoe construction.
University of Missouri Extension supports community well-being through initiatives promoting healthy environments, youth development programs, family strength building efforts and ecosystem resilience according to its official website. The organization serves as an outreach arm providing research-based education aimed at enhancing quality of life according to its official website, extending services throughout every county in Missouri according to its official website. It partners with county governments, state agencies and community groups according to its official website while offering educational programs spanning agriculture; family & consumer sciences; youth development; as well as community economic initiatives according to its official website.
For more information about caring for arborvitae or other landscaping concerns, residents are encouraged to contact their local University of Missouri Extension horticulture specialist.
