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Wednesday - August 06, 2008

From: Monterrey, Mexico
Region: Other
Topic: Green Roofs
Title: Plants for green roof in Mexico
Answered by: Nan Hampton

QUESTION:

Hello! I am checking local plants to plant on a Green Roof, and am researching on which are mostly to survive better. Is it possible to plant the following on a green roof?? (Root depth needed, basically) and would the fact of being on a green roof affect the time of growth?: lupinus texensis, pinus culminicola, cheilanthes alabamensis, vitis cinerea, cordia boissieri, sophora secundiflora, mascagnia macroptera, rubus aff. trivialis, eschscholtzia mexicana. Thank you!

ANSWER:

First, I hope you have visited our Native Green Roof page where you will find a link to a Species List from Wildflower Center Research. These are plants that are currently being tested for growth on a green roof. As Dr. Mark Simmons said in the answer to a previous question about what to plant on green roofs:

"We tend to favor locally native plants that can tolerate a wide range of climate and soil conditions (i.e. those which have "generalists" traits)—most of the common and widespread prairie grasses and forbs would fall into this category. Selecting your species from this palette would increase your chance of success..."

The native plants available for green roofs in Monterrey, Mexico will be a bit different from those recommended for green roofs in Texas, but many of the species from the list would work there. You should review that list for potential species to use. Greenroofs.com also has a list of recommended species. You will note that, with the exception of Bignonia capreolata (crossvine) on the Wildflower Center list, neither of these lists has woody species. This is for a good reason—woody species are going to require more soil to accomodate their roots. Your list contains several that are woody plants—trees and shrubs.

Here is an assessment of the plants you mentioned:

Lupinus texensis (Texas bluebonnet). Although it might do just fine there, you will have only about a 1 month period when it blooms. Otherwise, the plant itself is very low and nondescript and dies shortly after the seeds mature and drop. It is an annual and thus would need to be reseeded each year.

Pinus culminicola (Potosi piñon) is a mountain species and endangered. I couldn't find any information about its root system. Many of the conifers have tap roots and these would definitely not be a good feature for green roof plants

The habitat of Cheilanthes alabamensis (Alabama lip fern) is calcareous rock slopes in shade so it is not a good candidate since roof plants can expect full sun.

Vitis cinerea (winter grape) has a branching tap root system which would not be appropriate for roof planting.

Cordia boissieri (anacahuita) is a shrub or small tree that does not have a tap root system and could possibly work well on a green roof. The TAMU Extension Service says: "Olive trees have shallow root systems so they do not need a deep soil, but the soils must be well-drained."

Sophora secundiflora (Texas mountain-laurel) have long tap roots according to Jill Nokes in "How to Grow Native Plants of Texas and the Southwest and, thus, would not work for the green roof.

Mascagnia macroptera (yellow butterfly vine) could potentially work well.

Rubus trivialis (southern dewberry). I found conflicting information about whether this species has a tap root or shallow roots.

Eschscholzia mexicana (Mexican gold poppy) would probably be a good species although it, too, is an annual.

Since the climate in Monterrey is arid with high temperatures approaching 100° F. in the summer and lows occasionally near freezing in the winter, you need to use plants that will tolerate these extremes. If you want height (as your inclusion of several trees in the list suggests), why not use some plants in the Family Agavaceae (e.g., Hesperaloe parviflora (redflower false yucca)) that can tolerate the extremes. Look around in the ditches and vacant lots for plants growing there that have to make do with harsh sun, wind, and little rainfall. These will give you an idea of what kind of plants are going to be the most successful on a green roof in your area.

There is also a new article "Green Roofs Differ in Building Cooling, Water Handling Capabilities" on the University of Texas web page.

 

 

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