We've been working with Resurrection fern also - and I love this plant. Resurrection fern, Polypodium polypodioides, was the first fern in space - going up on a 1997 Space Shuttle Mission to see if the roots would absorb water in a space capsule.
Both of these plants, the Allium and Resurrection fern have unique root characteristics.
We call plant root structure by the name - 'Root Architecture'.
Green roof design has unique root structure and root architecture requirements.
Unless you have a huge potable water or well water source and are going to pump all that water up on a roof to keep plants up there watered, then your green roof plants need to be somewhat drought tolerant.
Certain root architecture patterns support plant acclimation to drought conditions better than others.
Remember, Florida's rainfalls usually are short, afternoon events of 1/2" or less and because rain generally occurs between the hotter months of the year - June - September, there is a tendency for it to evaporate quickly.
Except for hurricanes and tropical storms, rain events in Florida are usually over relatively quickly.
Meaning green roof plants have to scramble to grab the rain water.
Also recall, most green roof plants do not like wet roots (wet feet) so the soil must be well drained.
Proper green roof plant root architecture is crucial for providing a Florida extensive green roof plant with the advantages needed to survive a Florida vegetated roof.
Examine the diagram below showing the root architecture of a green roof plant raised in a one gallon standard nursery container and then a green roof plant raised on a green root mat.
The plant raised on the mat possesses 8 times the amount of Root-Rain surface contact area as the same size plant grown in a nursery container.
|Green Roof Plant Root Architecture - Florida Extensive Green Roofs - MetroVerde|
So when the afternoon 1/2" rainfall (13mm) event occurs and every drop is important - the green roof plant with the appropriate root architecture will sequester the most water.
More stormwater is captured, runoff is reduced, plants acquire necessary water volumes, plants have less of a tendency to uproot in high winds, and more.
Green Roof Plant Root Architecture is important to the success of a green roof.