Green Corner: Robertson Roots Go Deep...Or Do They?

There's always something interesting to report when it comes to the living systems at the Robertson Building.
For this edition of the Pipeline, we're going to take you deep into the underworld of root systems on the green roof.  Typically, when a seed germinates, it plunges a strong primary or "tap root" downward into the soil. The
objective of a tap root is to grow deeply into the soil to anchor the new plant and access nutrients and moisture for energy production and photosynthesis. Plants with tap roots are difficult to transplant - think about the last time you tried to urge a dandelion out of the ground! Even if you break the top off, the long taproot stays in the
ground and can re-generate an entire dandelion plant all over again.  

Among the many extensive greenroof plants on the Robertson Building, we have a species known as rudbeckia-
laciniata, or the Green Headed Cone Flower, located in a large patch on the east side of the roof. By mid August we anticipate that they will become a tall, vibrant, yellow stand of plants, just like  they were last season. This spring we noted that the cone flowers were in good health and had wintered well. In fact, the species was becoming invasive. We were amazed to discover how the plants root system had adapted to the shallow planting media. The tap roots were all growing horizontally or parallel to the roof membrane. This observation is encouraging for green roof advocates on many fronts. Firstly, it dispels the rumour that plant roots penetrate roof membranes and cause roofs to leak. Secondly, this form of root adaptation tell us that tap roots can sense resistance and make the micro and macro cellular changes that it takes to survive, while still bracing the plant effectively, despite the shallow environment. Interestingly, these roots were all found pointing in exactly the
same direction, which further stabilizes the plant structurally against the prevailing northwest winds on the
Robertson roof. These amazing adaptive roots show us how much we still have to learn about how greenroofs
contribute to  new and exciting natural environments. 

Stay tuned for more green updates. For more information please call, Beth Anne Currie, 416.595.5900 x21