Green Roof Plant Root Architecture

A while back we looked at green roof plant root architecture and the benefits of green roof plants possessing a broad, shallow root structure rather than a narrow, deep root structure.  Click here to review the blog post information.

The diagram is posted for review here.

Green Roof Plant Root Architecture Comparison - MetroVerde

Real life Green Roof Plant photos of the two types of root architecture are posted below:

Root Architecture - Poor Green Roof Formation 

The photo above typifies the normal nursery container plant root structure - narrow and deep.  This is not a good root formation or architecture to begin a green roof with.  Note the following photos of a plant grown on a mat.  I've cut the mat out of a green roof that had a 2" engineered soil layer.  The plant had grown on the roof for approximately 3 years or longer.  The green roof system was non-irrigated.

Green Roof Plant - Root Architecture 1 - MetroVerde

Green Roof Plant - Root Architecture 2 - MetroVerde

Green Roof Plant - Root Architecture 3 - MetroVerde

Green Roof Plant - Root Architecture 4 - MetroVerde

When I removed the mat section I cut out about twice the diameter of the plant crown or habit (form diameter) thinking I'd capture all the root mass.  Upon further examination the plant had extended its roots over triple the area I'd cut.

Note how the roots have grown and woven themselves into the mat - providing an anchor against high winds and allowing for use vertically.

The root architecture of plants grown in mats exemplifies the benefits of growing green roof plants in mats.  Roots do not like to be bound up with limiting walls.  It you do not use mats, then use large tray systems.

With time, green roof plants with access to a large, monolithic and non-sectioned growing space will eventually 'move' to the best spot for their particular needs - on the roof.

The same basic principle applies to living walls.  A monolithic fabric with no limiting sectional structure will allow the plant to choose the best spot for successful, long tern growth.