Bonsai style preparation for green roof plants in Florida is time consuming yet delivers results and is worth the time and effort. MetroVerde green roof plants are grown with no additional fertilizer and rely on native rainfall events for irrigation. The plugs shown above are one year old, having spent their life growing under conditions similar to what they will experience on the roof.
The plants shown here are Allium species - and we are experimenting with the native 'nodding onion' found growing across the southeastern United States.
I highly recommend anyone considering a vegetated green roof to plan well in advance and 'bonsai' the plants - acclimating them to the same harsh environment they will spend their life in on top of a roof.
Remember the 5 'H's of the Southeastern US and Florida - Hurricanes, High Humidity, Heat Extremes (Pressure cooker style), Hard Frosts , and High Winds that dry and dessicate plant leaves.
I wrote a blog entry last year about sprouting green roof plant seeds on the roof they will be planted upon - and though not always practical. In any event, growing the plants under non-fertilized, non-irrigated conditions until they are solidly established is a solid approach to plant success once on the roof.
I've seen too many vegetated roofs fail after the designer and installer use plants pumped full of fertilizer, not hardened off and used to significant amounts of irrigation. Once on a roof, the plants experience shock.
Natives are great - adapted native species excellent too.
Remember, prep your plants long before planting on the roof.