Deep planting of young trees—defined as the burial of the root collar below soil grade—is widely recognized by practitioners as an improper technique that can impair tree development and establishment. Despite this knowledge, research has shown that urban trees are frequently planted too deeply. To better understand the impacts of planting depth on the urban forest, we conducted a literature review of peer-reviewed and professional studies relevant to the effects of planting depth in urban trees. Most studies reported effects on tree establishment (34%), growth (23%), and root development (22%). A general conclusion across reviewed articles was evident: trees planted too deep exhibited higher mortality, slower establishment, and reduced growth, primarily due to poor root development. Effects of planting depth were also species-specific—Norway Maple (Acer platanoides L.), Turkish Hazel (Corylus colurna L.), White Ash (Fraxinus americana L.), and Green Ash (Fraxinus pennsylvanica Marshall) showed minimal differences in performance when deeply planted, while Baldcypress (Taxodium distichum L. Rich), which tolerates anoxic conditions, performed better at or below grade than when planted above grade, although the findings in these studies only measured the effects of planting depth relative to limited measured parameters. We also compiled a reference table that links tree species to their performance based on planting depth. These findings highlight the critical role of planting depth in shaping root architecture and long-term success, emphasizing the need for adherence to best practices concerning proper planting, tree maintenance (e.g., mulching), and production in the nursery.
Jamie Lim (Fri,) studied this question.