Our recommendation will always be to provide tree roots with the substance nature intended. In the long term, urban tree health is inextricably linked to the soil the roots are growing into. GreenBlue Urban are continually studying this subject and our goal is the provision for the urban tree of a soil which mirrors, as closely as possible, a ‘forest floor’ soil condition and content.
Our studies have led us to excavations in natural forests as well as urban tree planting sites around the UK, seeking out the most favourable rooting conditions – and their common characteristics. This has revealed that uncompacted, free draining fertile loam soil is the most root friendly substance on the planet.
Sand alone is not sufficient – or the Sahara would not be a desert. Rocky terrain likewise – without soil in, is not conducive to a healthy long-term rooting structure.
Roots in rock soil substrate mixtures, tend to be artificially elongated as they have to travel further to access nutrient and moisture – hence the need in this type of system for huge volumes (typically -50 cubic meters per tree, provides approximately 12 cubic meters of actual soil for roots.)