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Home HortScience Colorful Native Plant Recommended for Mediterranean Green Roofs
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ATHENS, GREECE—Green roofs are becoming a popular way to improve the environment, but they aren’t a quick fix for every situation. Two concerns affect the feasibility of green roofs in the Mediterranean region. The first is the semi-arid climate. The second is the ability of old structures to withstand the weight of a green roof.

In an effort to understand the options, Panayiotis A. Nektarios of the Agricultural University of Athens led a team of researchers in experiments to test the drought tolerance of an endangered native plant. The scientists chose Dianthus fruticosus, an endangered species that grows in rock crevices in the Mediterranean region. The plant can withstand extreme temperatures and drought and has strong root systems to help anchor it in high winds. "Native plants are preferred for green roofs because they have already adapted to the local climate, have a proven track record for their care and ability to thrive, and improve the area's biodiversity by attracting pollinating insects and improving other flora and fauna," Nektarios said.

The researchers planted 160 Dianthus fruticosus plants in one of four variations of plots: substrates including a small percentage of soil, substrates without soil, and at a depth of either 7.5 or 15 cm. The plants were watered every 3 days during spring establishment, after which time they were subjected to a simulated drought.

After 2 month of simulated drought, the plants were measured and three plants from each plot were weighed. The coloring of the plants and amount of chlorophyll were also measured. The results showed that plots with soil retained more water during the drought. The shallower growing plot was moister after watering, but also dried faster, so that the moisture level of the shallow and deeper plots were almost the same by the time of the next watering some 10 days later.

Plants grown in the deeper plots had more leaf mass, which the researcher say is most likely the result of their access to more moisture being stored in the planting medium and/or the amelioration of substrate temperature extremes. The coloring of these plants was also better than those grown in shallow depths "This further substantiated the conclusion that the depth of the substrates seemed to be the most influential factor on D. fruticosus physiology when grown on green roof systems," said Nektarios.

During the drought period, the amount of irrigation was the most observable difference between the variations, with the heavier-watered plants faring better. Those plants in deeper beds also did better by the end of the drought regardless of soil in the planting medium.

The study, published in HortScience, concluded that Dianthus fruticosus has "very good potential" for Mediterranean green roofs as the plants grew successfully in shallow depths with the least amount of irrigation.

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The complete study and abstract are available on the ASHS HortScience electronic journal web site: http://hortsci.ashspublications.org/content/46/8/1208.abstract

Founded in 1903, the American Society for Horticultural Science (ASHS) is the largest organization dedicated to advancing all facets of horticultural research, education, and application. More information at ashs.org


 

Original Article:

Green Roof Substrate Type and Depth Affect the Growth of the Native Species Dianthus fruticosus Under Reduced Irrigation Regimens
Panayiotis A. Nektarios, Ioannis Amountzias, Iro Kokkinou, and Nikolaos Ntoulas
HortScience 46:1208–1216. [Abstract][Full Text][PDF]

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