Tree Cavity in Deck Tree: Don't Fill, Fertilize

Large Hollow in Trunk: Assess Risk, Not Just Appearance

A 12″×4″ cavity 5 ft up in a mature shade tree (likely a honeylocust from the seed pod description) indicates internal decay from a past wound. Decay fungi only digest dead heartwood.

Cavity Filling: Outdated & Harmful

Cement fills create rigid columns that don't flex with the tree, causing new wounds and trapping moisture—accelerating decay. Modern flexible foams are cosmetic only; they add no structural support.

Best Practice: Promote Tree Vigor

• Water: 1 inch weekly during dry spells (pan method).
• Fertilize: 1 lb 10-10-10 per inch trunk diameter annually, broadcast and watered in.
• Monitor: Watch for large dead limbs, new cracks, or lean changes.

If the canopy is full and green, the tree is compensating well. Have an ISA Certified Arborist evaluate structural risk if the tree overhangs the deck.