In a 10-week field study, native Pentaspadon motleyi seedlings inoculated with arbuscular mycorrhizal fungi (AMF) grew five times taller and thicker than untreated seedlings when planted along a degraded waterway. AMF-treated seedlings also developed 2–3× more leaves, larger leaf area, and healthier, more fibrous root systems, all traits linked to better survival in flood-prone conditions. The results show that fungal inoculation can materially strengthen young trees during early establishment.