Dichlobenil Near Magnolia: Safe If Roots Protected

You plan to apply dichlobenil (Casoron) on soil near a magnolia before installing a hot tub on pavers. Will it hurt the tree?

Herbicide Safety

• Dichlobenil is a pre-emergent; low mobility in soil. Properly applied, it won’t harm established magnolia.
• Risk comes from root damage during installation, not the chemical.

Real Risks to Magnolia

1. Root compaction/cutting: Hot tub weight + pavers + base prep can crush or sever roots. Magnolia roots are shallow (top 2 ft) and extend 1.5× canopy width. >30% root loss causes dieback.
2. Drainage chemicals: Hot tub water (chlorine, bromine, salt) draining near roots can kill them.
3. Leaf litter: Magnolias drop leaves year-round—expect cleanup in the tub.

Mitigation

• Hand-dig tub base; avoid large root cutting.
• Direct drainage away from root zone.
• Apply dichlobenil only in areas not directly over major roots (follow label).
• Mulch root zone to reduce compaction.

Bottom Line

Dichlobenil is safe if labeled rates are followed. The hot tub installation is the real threat—protect roots during construction.