Is it possible to plant a Katsura in a raised bed with limited soil depth?
Thank you for contacting Toronto Master Gardeners to inquire about planting your Katsura tree (Cercidiphyllum japonicum) in a raised garden bed. These trees are grown for their beautiful shape and heart-shaped leaves with striking colours. They require very little maintenance in our gardens and make wonderful shade trees.
Katsura tree growth rate is considered fast for a tree. The mature size for a Katsura tree is a height of 40-60 feet with a spread (width of the tree crown) of 25-60 feet. The crown size is important as the roots of the tree will spread out horizontally just under the surface to even further than the size of the crown. Katsura trees have shallow and wide roots. They grow best in rich, moist, well-drained soils and are drought-sensitive. Given this, growing Cercidiphyllum japonicum in a raised garden bed is not recommended for two key reasons. #1 – the size of the roots will quickly outgrow the size of your raised bed. The roots at mature size will reach at least 25 feet across. Your growing Katsura tree will find its roots constricted by the raised bed (impacting the stability of the tree) or more likely, the roots will find a way to grow through the sides of your raised bed. #2 – Soil in a raised bed dries out faster than in the ground as raised beds have more exposure to the sun and increased air circulation. Katsura trees are sensitive to drought and would need to be watered frequently if planted in a raised bed.
There are a number of smaller evergreen and deciduous shrubs (including Ontario native plants) that would be more suitable to be grown in a raised garden bed. Good luck with your planting!
Information on transplanting a Katsura tree can be found at: https://www.torontomastergardeners.ca/askagardener/moving-a-recently-planted-katsura-tree/
Information on raised beds can be found at: https://www.torontomastergardeners.ca/askagardener/raised-framed-garden-beds/
Additional reading: Growing Trees and Shrubs Organically