Thursday, November 10, 2011

Green Roof Plants - choosing between those plants that produce seed and those propagated vegetatively

When choosing plants for green roofs one is always faced with a decision to specify those species with a tendency to bloom and flower then set seed, or on the other hand go with those plants who normally are propagated primarily by vegetated cuttings.

Green Roof plants setting seed in Jacksonville, Florida
 Yet the decision is not a simple one and carries far reaching consequences.  Arguments for and against highlight the many benefits and disadvantages for selecting either approach.  I prefer to integrate in so many plants who reliably produce viable seed for the following reasons discussed below.

November seeds sprouting on a Florida Green Roof
Seed provide variability.  Like a roll of the dice, the many combinations of predictable but also unpredictable color, patterns and texture always provide a surprise waiting once plants set seed and those seed germinate into a new generation.  Because of inherent variability, seeds are generically difficult to remove from the open source system and patent.  Plants propagated via cuttings or asexual reproduction are much easier to protect under intellectual property rights laws and remove from public domain.  So by adding plants who reproduce by seed to your green roof design, you ensure for the time an ongoing, royalty-free plant source season after season.

Green Roof Salvia lyrata and green roof seeds sprouting
Longing for seasonal variability including color hue shifts, texture changes and other plant responses is a fundamental part of humankind's side by side relationship with the plant kingdom.  Plants who do  not rise and fall with nature's cycles seem almost 'plastic' to me.  Granted I use these 'plastic' plants to create central design structure and they serve faithfully providing green and form month in and month out.  But these structure plants are only a backbone.  The skins are the many hundreds of species, genus and families of flowering ephemeral and persistent native wildflowers, grasses and food plants.

Once established, seed producing green roof plants are an economic & ecological benefit

Familiarity with the signs of plant growth teases the senses like aroma from fresh baked bread.  The Salvia lyrata in the above photo for instance is preparing to cover certain areas of the green roof with her wonderful lavender spring flowers, one of the first sights across the roof as winter recedes.

Life is a complexity of changing interactions.  Green roof designers can tap into the interest of nature's spectacular array of surprising variability by using lots of plants who seed and reseed.

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