Construction workers are busy putting the final touches on the Morris Arboretum’s new Horticulture Center at Bloomfield Farm. Located across the street from the public portion of the Arboretum, the Horticulture Center is the first new structure to be built on the 167-acre site since the 19th century. It was designed to meet LEED’s platinum green building rating, boasting geothermal heating and cooling; a rain collection system that includes a large cistern to hold water to be used in the lavatories and two green roofs covering the heavy equipment garages.

In addition to her many other duties as the horticulture section leader, Louise Clarke has been in charge of planting the green roofs. The Current visited her on site to discuss the new roofs and the career change that led the former clinical laboratory scientist to a new profession outdoors.

Q. What is Bloomfield Farm?
A. It is part of the Morris Arboretum, but it is a separate parcel that John Morris bought in the early 1900s to augment what he already owned across the street in the area called Compton. And at that time it was agricultural, hence the name Bloomfield Farm. But what you see today is not a working farm. It’s approximately 65 acres. Normally, it’s closed to the public. We have research plots here; our materials handling is here and trees that are accessioned as part of the living collection are also residents here. That’s part of my job, to curate the collection. ... There are over 1,000 accessioned plants here and I look after their health.

Q. How long have you been at Penn?
A. I started here in June of 2008, as an intern at the Bloomfield Farm section. I was doing a career change. I had been a clinical laboratory scientist. I had done cancer diagnosis in a pathology laboratory. But I was always interested in horticulture, and I decided to follow my passion.

Q. What attracted you to this profession?
A. I love horticulture. That was my primary focus. I like to work hands-on. It’s great to be outdoors. My initial challenge was to learn the trees in the living collection that I am responsible for, to learn the lay of the land, the history, and to be able to convey that to others, because part of my job is teaching. I work with the interns, teach them basic horticulture skills, how to manage the collection, things like pruning, operating the equipment, mowing, transplanting, all the kinds of skills you need to work here successfully.

Q. What are your responsibilities this time of year?
A. Things are growing, so it’s mowing season once again. We also have spring planting, which has begun. All the beds in this area, around the new building, will be planted, mostly with North American natives. That will be part of my responsibility in the next few weeks. My priority right now is to plant the green roof.

Q. Can you talk about the green roof?
A. Well, we have two. The smaller one is on our four-bay garage. It is about 2,500 square feet, and that roof is an ‘extensive’ green roof. Extensive refers to the depth of the growing medium, which is approximately four inches. That is fairly shallow for any plant’s needs. The plants that are up there are sedums—about eight species with different leaf shapes, leaf color and different flowering periods—adaptive to the tough conditions up there: full sun, wind, potential drought, high temperatures, low temperatures.

Q. What are the advantages of having a green roof?
A. Insulation is one of the properties of this kind of roof, but that’s not very applicable to our garages because they are not tight buildings. The roofs also have the ability to help mitigate the urban heat island effect. The plants provide filtration of water and air pollutants. They are designed to capture water, especially in heavy rainstorms, and reduce peak flow volumes, which is important for water management. They will then eventually transpire that water back out through their leaves, which helps to cool and humidify the air. In cities, green roofs can really help us deal with storm water management issues, which is critical because we’ve paved so much area and storm water has nowhere to go. Green roofs help keep water out of our sewers, which are already overloaded in heavy storms. And aesthetically, they are pleasing to look at.

Q. Will the extensive roof be different colors during different times of the year?
A. Yes. Right now, as you see, it’s kind of a burgundy, bronzy red, which is still kind of its winter coloration. It will green up more, and then it will flower. At certain times we’ll have white flowers up there, pinks, yellows and that will be all the different species as they come into their bloom period.

Q. Tell me about the second roof.
A. That one is the ‘intensive’ roof, and that gives us a depth of about eight inches. That one is about 3,700 square feet, and it is much more labor intensive. We are planting shrubs up there, perennials, a few more sedums and grasses. We’ve even incorporated some things like yuccas and agaves. It’s going to be a big ongoing experiment to see what is happy up there and what is not.

Q. Who decided what would go up there?
A. The landscape architects we worked with—Andropogon Associates—gave us a preliminary plant list, which we reviewed. Then the horticulture staff here, with the curator, decided what we liked on that list. We supplemented it with things we think will do well, and some things we are just going to experiment with. For example, we are going to employ some spring flowering bulbs, so we might have crocus, or iris up on the roof.

Q. Is this the first green roof you have ever planted yourself?
A. Yes, it is, and it’s a wonderful opportunity to be involved in this. It’s still a relatively new thing, even though historically it’s not. You could consider the ancient hanging gardens of Babylon as the first known green roof. ... What we have as guidelines today come from Germany because they were pretty much pioneers in the current green roofing industry. But Germany is a small country and the climate is pretty similar within their small area. So, the research that needs to be done here needs to address our varied climate.

Q. Horticulture is not just a fancy word for gardening, is it?
A. No, it’s not. It encompasses a lot of sciences. It encompasses soil science, a smattering of geology, plant ecology and restoration practices because we deal with a lot of invasive plants out here—honeysuckle and a vine called Oriental bittersweet. I love my job. I know lots of people can’t say that, and I consider myself really lucky.