plants for a green roof

I am trying to select plants for a green roof on Lopez Island. I would like to use some native plants, and not have to do too much weeding. Can you help me?

The Miller Library has a booklist on green roofs which includes weblinks. With respect to weeds, as a former professional gardener I don’t believe there is a “maintenance-free” garden. However you may be able to come up with a freely seeding grass (Festuca ovina var. glauca comes to mind) that would do well and look good with other plants.

Regarding Pacific Northwest native plants (i.e., grasses), I recommend using a native plant book (such as Pojar and MacKinnon’s Plants of the Pacific Northwest Coast) and searching for those which suit the conditions of the site. You may also find King County’s native plant
guide useful, as it is searchable by site requirements. Washington Native Plant Society offers a similar plant selection guide. There are also native species of Sedum.

The book Green Roof–a Case Study by Christian Werthmann (Princeton Architectural Press, 2007) evaluates green roof plants and planting techniques, and includes observations regarding soil depth, the factors affecting desiccation (i.e., metal edging and the planting medium/size of the plants used), and density considerations. Here are some of the conclusions of the case study:

p.69-insects and other invertebrates need >6″ of soil to survive the cold;
drought tolerance increases with soil depth; probability of seed germination also increases with soil depth
p.76-erosion control (bird repellant?) made from a degradable straw mat (such a mat may be useful for preventing birds from pulling up the plugs)
Plants:
p.95-sweet fern Comptonia peregrine-not too vigorous, suffered from weed infestations
p.96-prickly pear Opuntia fragilis-did well
Phlox subulata, Silene caroliniana-did well
Sedum telephioides, S. lanceolatum, S. stenopetalum-suffered from heat, drought, and birds-these were replaced with European sedums (S. album, S. reflexum, S. spurium, S. cauticola, S. sexangulare, S. floriferum, Sempervivum tectorum, Orostachys boehmeri) and not planted as plugs but as larger plants that started in the green roof substrate (reducing transplant shock)
p.100-mixed prairie perennials with sedums (in 6″ soil), which filled in when perennials died-the architects note that there is no record of prairie plants doing well on green roofs, therefore the backup with succulents-they also note that metal roof edges speed up desiccationPerennials included ice plant (Delosperma nubigenum; my note: be careful about this, as it’s a noxious weed in California and if it spreads by seed, it might become a problem on Lopez); flameflower (Talinum calycinum); Eragrostis spectabilis; Allium schoenoprasum; Allium cernuum; Bouteloua gracilis; Elymus virginicus; Achillea millefolium; Tradescantia bracteata; Solidago nemoralis; Artemisia ludoviciana; Coreopsis verticillata; Asclepias tuberosa; Rudbeckia hirta

p.105-in 3″ soil with nearby metal (and thus an overheating issue), they used proven sedum species; heat from metal can be reduced by using aluminum (proved cooler than wood)

p. 108-conclusions: use a combination of indigenous plants with “successful green roof performers”-thin soil and high light “even overtaxed the hardiest succulents”-soil depth and temperature extremes made a big difference; even a slight difference in soil depth in a harsh environment can mean the difference between success and failure-continuous care and maintenance in the beginning is important for success-plugs grown in peat moss were less successful, since completely dried-out peat moss repels water-dense plantings (and/or rapidly spreading plants) important because bare soil gets hotter than soil covered by a plant.

Sedum as a green roof material

I am trying to find a Sedum expert to help figure out better uses for this plant as a green roof material. Can you help point me in the right direction? Also, are there native Sedums?

Here is a list of the books the Miller Library has on this subject, including the following titles:

Planting green roofs and living walls by Nigel Dunnett and Noel Kingsbury (Timber Press, 2004)
Ecoroof: questions & answers by Portland Environmental Services (Portland, Or. : Environmental Services, 2004)Note: Portland’s Ecoroof Program is a cooperative effort of the Bureau of Environmental Services and the Office of Sustainable Development. The program promotes ecoroofs by researching ecoroof technologies an providing information and technical assistance to community members.
Green roofs: their existing status and potential for conserving biodiversity in urban areas by Ecoschemes Ltd (Peterborough: English Nature, 2003)

An article by Jessie Keith from The American Gardener (March/April 2005, pp. 38-41) mentions different types of Sedum appropriate for a green roof, which I will list here:

Sedum album ‘Coral Carpet’
Sedum ‘Green Spruce’
Sedum lydium
Sedum rupestre (syn. S. reflexum)
Sedum sexangulare
Sedum spurium ‘John Creech’
Sedum telephium ‘Matrona’

You might also want to speak with someone at the Cascade Cactus and Succulent Society of Washington State.

There are some Sedum species native to the Northwest.The Sedums that are native to the Pacific Northwest, according to
The Encyclopedia of Northwest Native Plants for Gardens and Landscapes by Kathleen Robson, (Portland, OR: Timber Press, 2008) include:

Sedum divergens Cascade stonecrop
Sedum laxum Roseflower stonecrop
Sedum oreganum Oregon stonecrop
Sedum oregonense Creamy stonecrop
Sedum spathulifolium Broad-leaved stonecrop
Sedum stenopetalum Wormleaf or narrow-petaled stonecrop

Two additional species are listed in Plants of the Pacific Northwest
Coast, edited by Jim Pojar and Andy MacKinnon (Richmond, WA: Lone Pine Publishing, 1994):

Sedum integrifolium Roseroot
Sedum lanceolatum Lance-leaved stonecrop

vegetables to grow on roof gardens

I’d like to plant a vegetable garden on my roof. It will be in a feed trough about 8 feet long, and 2 feet wide and deep. I’m wondering what I can add to lessen the weight of the container (so it won’t just be filled with potting soil and compost). Also, any recommendations for which vegetables to grow would be great–things which are fairly easy and don’t have enormous roots!

To lighten the load of your container, a lightweight organic material like hazelnut shells might make a good bottom layer. You could use perlite, but that may actually be heavier than the nut shells. Here is information about sources of hazelnut shells:
Oregon Hazelnuts (a website of hazelnut growers) (lists several sources)
A Washington State source, often found at local farmers’ markets, is Holmquist Hazelnuts.

The book The Edible Container Garden: Growing Fresh Food in Small Spaces by Michael Guerra (Simon & Schuster, 2000) has a section on rooftop containers, and recommends (after you’ve consulted a structural engineer) using lightweight, well-draining compost, and setting your container(s) on timbers to help with drainage. According to the book, the best candidates for containers are potatoes, chard, lettuce, radishes, shallots, bush tomatoes, eggplant, zucchini, squash, dwarf carrots, dwarf beets, mustard and Asian greens, and runner beans. More difficult are cauliflower, cabbage, Brussels sprouts, kale, parsnips and other deep-rooted vegetables.

The following links may be of interest:

University of Maryland Cooperative Extension

Vegetated Roofs from Oregon State University Extension

Article about the Reading International Roof Garden (Britain) from The Guardian by Emma Cooper (and another article by this author in Permaculture Magazine #53).

Keyword: Green roofs (Gardening)