Plant Selection

Over the past few weeks, the team has been working extensively on researching the types of plantations to use in our green roof garden. The roofs of buildings can be a cchallenging condition for plants to grow because of elevated temperatures, wind exposure and high light exposures. In the case of 30th station, this condition is especially true since it does not have any shadings of other high rises over it.

 We then looked into the weather of Philadelphia, especially West Philadelphia:

1. The driest month in Philadelphia is February with 2.74 inches of precipitation, and with 4.39 inches July is the wettest month.
2. Philadelphia's coldest month is January when the average temperature overnight is 25.5°F. In July, the warmest month, the average daytime temperature rises to 85.5°F.

From this information we learned that Philadelphia has a radical climate change over the four seasons, which means our plants need undergo a harsh winter(snow and low temperature) and dry months.

50% of our plants will be all seasons sedum because Sedums and other succulent plants are often used on green roofs because they are tolerant of the dry conditions found on most roofs.(source) We then made a list of particulars for our plants and came up with a plan which we think would be efficient for the garden.

1. Vegetation: minimum 95% coverage ·
1. Fiber/soil base: approximately 1” thick
2. Size: 12”w x 24”l x 2-3”h (2 sq. ft. per tile)
3. Max weight: 5.48 lb./sq. ft. fully saturated
2. Maintenance: Minimal maintenance requirements once established

Excursion to the Free Library roof top

In order to gain a better understanding of green roof installment and plant selection, the team went on a trip to the Free Library of Philadelphia where a semi-intensive green roof was installed in 2008. According to the library website, the garden contains more than 5,400 plants. Sedums include Murale White Stonecrop, Blue Cadet Creeping Sedum, and Blue Spruce Stonecrop along with grasses such as Blue Grama, Feather Reed Grass, Blue Fescue, and Prairie Dropseed. This green roof was the first green roof on a government-owned building in the city of Philadelphia and has a beautiful view of central Philadelphia from the terrace (Figure 1). 

Figure 1

The team was able observe the garden and its drainage system closely(Figure 2). We also talked to the library officials and hope to develop further contact with the lead designer of this garden to gain more insights. 

Figure 2