Nature Irrigated Green Roofs - how much water do you need!

Nature is amazing.  It has not rained for several days here and though we did recently have a little rain we are still far below our normal.  In fact Jacksonville is still classified as officially experiencing severe drought conditions.

National Weather Service Drought Index

Yet nature provides ample water, even in times of drought here in the form of water vapor.  Good green roof design takes advantage of all sources of water, including morning dew.

Nature's irrigation - morning water vapor

I am constantly amazed at just how much water rests on the green roof plants some mornings.

As though an irrigation sprinkler has been turned on across the roof, opportunities exist for the plant designer to use those species capable of condensing (those with fine leaves, hairs or waxy surfaces) to capture the water then direct the droplets to the green roof planting media below.

Working with an international hotel chain to improve their landscape vegetation I was asked to diagnose why a large collection of very big planters were doing so poorly.  A large roof overhang directly above prevented morning water vapor from reaching the plants.  However, only a few feet over and out from under the overhang other planters looked lush.

Fog and morning dew can contribute an important source of nature supplied irrigation.

I make it a regular habit to walk green roofs early, middle of the day and late.  Surprises abound always.  This morning I was amazed at just how much water was on the plants.  Who needs a sprinkler?