My Green Roof 16 years later and I am still hanging in there with it

I was on a team that proposed a green roof at the Department of Interior headquarters.  I read about green roofs and their benefits in slowing down stormwater, extending the life of roofs, and more.  I saw the green roof at Sleeping Lady Resort.  I was inspired to build a green roof on my toolshed. I knew why but I had the challenge of learning the details of how.

I am a long-time gardener and landscape and irrigation consultant, so I quickly figured out the plant part.  I bought sedums and native, wild strawberries.  And the strawberries spread well…out of their pots and all over the ground where their pots sat for almost a year while I learned and decided on the construction details.

I read about and visited with Patrick Carey, who was leading a green roof effort back then in the Seattle area.

He showed me a green roof and explained the plants, planting medium, and care.  But it looked sparse to me.  Next, he showed me a pile of green roof materials and explained them.  He helped address some of the challenge of how to do it.

I did more research and learned that the extra weight of the soil, the water the soil would hold, and the additional materials on the roof would need more support underneath them.  I now felt ready to at least start work on the extra support needed under the green roof.  My friend Tom Hovde helped me increase the support under the roof from 24” on center 2x4s to 12” on center.  And we put more foundation support in under the cantilevered parts of the floor.  And more support over the door and window.

Now it was time to decide on which basic materials to use in the green roof.

I finally settled on adding another layer of plywood, then a pond liner of that, next a drain mat, and sustainably grown and harvested local lumber to frame around it and for walkways.

Thankfully I found Albie, a local Vashon carpenter to work with, to help solve my challenge of how exactly to install all those materials on the roof.

Once the support system was in place, I could finally add the soil and the plants that were spreading through my garden below.  I went against the advice I received from a few people, and I created a high-quality soil mix that I made myself with compost to keep the plants happy.  I believe that decision was one of the keys to the success and good health of the green roof.  While it is true that sedums can get by on minimal water and soil, based on my gardening experience I felt they would thrive if given good soil.  And they have.  More friends Don Bollinger and Mark Ahlstrom helped me carry buckets of soil and flats of plants up the ladder to the roof.

After a few years the plants spread and filled in the green roof space including a lot of weeds.

The challenge of maintaining the green roof was not heard for me.  I knew from my home garden and landscaping and irrigation consulting experience that some weeding and watering would be needed.  And that the gardener’s shadow was the best fertilizer.

After about 5 years, the mix of surviving plants changed a lot. The strawberries and many of the native plants dies out and the sedums started expanding.  I speculate that the sedums came to dominate because I cut way back on supplemental watering.  I also cut way back on weeding but not totally.  And in 2 of the next 16 years as I noticed the depth of the soil shrinking, I added a thin layer of compost.

By this July, 16 years later, one variety of sedum, Sedum ruprestre “Angelina”, had almost totally taken over.  And the green roof is now totally full of plants.  A grape vine that we planted down below 5 years ago has grown up to the roof, across it, and down the other side.  And the apple tree has spread a few branches up to the roof.