Tuesday, November 22, 2011

Green Roof Plants - What Makes Roots Happy?

Removing older green roofs to allow for a new project has opened my eyes to the way green roof plant roots grow.  Root growth science is also know as 'root architecture'.  

As you can see, roots do not like to be constrained.  Though all roofs have a perimeter and roots must eventually reach a boundary, allowing the plants to reach out for  nutrients and water offers many benefits!

Tomato plant roots reaching out horizontally in the Green Roof hurricane weave


Having grown plants in pots for decades I can say with no uncertainty root bound plants are prone to disease and do not preform well in the long term.
Pot bound roots spiral around and around looking for room to grow
Green Roof trays must be large to prevent root binding patterns

Normal root architecture is best achieved by open growing systems on Green Roofs
To me, a photo is worth a thousand words and it is easy for me to see how roots want to stretch out.  Of course we've discussed the many benefits of horizontal root architecture in previous posts.  An example  of a shallow green roof application can be found here.

Let your green roof roots grow.  If you use a tray system make sure the trays allow for root crossover through adequate openings.

Roots need oxygen too.  When roots grow too deep or are strangled by other roots due to a lack of horizontal growing room the plants can suffer.  Providing adequate horizontal growing room ensures good plant development, unless you are using tap root plants (not too many of these are appropriate for green roofs).


3 comments:

Richard Boles said...

Nice diagrams, btw. Plants are like goldfishes in a bowl: they adapt to the container they are in. Roots take shape in their pots but not as always. They are known to get adventurous and find as much soil to cling on. So it's best to have them free-ranged on a flat tract of land.

lslwr357 said...

I had a professionally installed and I feel, partly inappropriately planted extensive green roof. After discussing 'natural 'and choosing specific plants they showed up with
monkshood and lilies which I didn't allow them to plant, but also I think Panicum Virgatum which i was later told needed much deeper soil. Also goldenrod that falls over and is mostly horizontal, I think because of the same problem ?
The company who also installed a rainwater retention tank, but never got it to work has disappeared. It is a new flat roof ; root barrier on top of waterproof membrane, drainage mat colbond3601, 2"ribbed roofmate insulation colbond3611R and 6" of growing medium blend is what I was told was placed there.
I am concerned that the roots for the grasses are too strong to pull up. I am thinking of cutting down and covering with black plastic to kill ? before trying to remove. Is it ok to leave some ?
What would you suggest ? Thanks, I guess this should be under "What makes roots unhappy

lslwr357 said...

I had a professionally installed and I feel, partly inappropriately planted extensive green roof. After discussing 'natural 'and choosing specific plants they showed up with
monkshood and lilies which I didn't allow them to plant, but also I think Panicum Virgatum which i was later told needed much deeper soil. Also goldenrod that falls over and is mostly horizontal, I think because of the same problem ?
The company who also installed a rainwater retention tank, but never got it to work has disappeared. It is a new flat roof ; root barrier on top of waterproof membrane, drainage mat colbond3601, 2"ribbed roofmate insulation colbond3611R and 6" of growing medium blend is what I was told was placed there.
I am concerned that the roots for the grasses are too strong to pull up. I am thinking of cutting down and covering with black plastic to kill ? before trying to remove. Is it ok to leave some ?
What would you suggest ? Thanks, I guess this should be under "What makes roots unhappy
Also, irrigate with drip hose ? or sprinkler set up ?