Up On The Roof

Those of you who make a practice of visiting Detroit Garden Works are aware that we have planter boxes on the roof. Eight rectangular heavy gauge sheet metal boxes span the entire width of the front of the shop. Designing and maintaining the planting for those boxes is a challenge. The weather conditions up there are extreme. It is always hot, windy, and completely exposed to whatever nature has a mind to dish out. Furthermore, whatever gets planted in them has to make some sort of impression from the ground. How are impressions made from afar? Light or pastel colors always read better at a distance. Large leaves are helpful. But the biggest impression to be made in this instance comes from the mass. This is 40 linear feet of boxes. The mass possible in these boxes is always in my favor, if I take advantage of it.

The design is not the only issue. Growing and maintaining plants on the roof has its own set of issues. It isn’t very practical to drag a hose upstairs, so we do have automatic irrigation in the boxes. You would think that would eliminate all of the water worries, but it doesn’t. The need for water changes all the time. Its very difficult to determine the moisture in the soil from the ground, although I personally can spot wilted plants from a long ways away. We have to get up on the roof to groom the pots, and feed them, so it is easy to check the water in person. Chelsea was up there to dead head the green and white plectranthus, and she noticed that the soil was bone dry in a number of places.  It was easy to figure out that some of the micro mist heads had become clogged. Once they were cleaned, the water was flowing again.

The box is planted with two rows. The back row is planted with bouteloua gracilis “Blonde Ambition”.  Commonly known as blue grama grass, or mosquito grass, this hybrid of the species has chartreuse flower heads which gives way to blond seed heads. Those seed heads that resemble mosquito larvae hang from only one side of the flowering stalk. This makes for a horizontal seed head that is as beautiful as it is unexpected. Hardy in zone 3, it is happy in dry to moderate moisture conditions. The seed heads hold through the fall, and in to early winter. For the full rundown, see the entry from the Missouri Botanic Garden website:   grama grass “Blonde Ambition”  Between each grass is the annual blue salvia cultivar, Cathedral Sky Blue.  Salvias are not especially showy, but the color of this cultivar is captivating. Mealy cup sage, or salvia farinacea, is notorious for sporting lots of foliage, and less in the way of flowers.  The grama grass is a perfect companion. It all but obscures the foliage of the salvia. The airy seed heads hover over the the more dense and static salvia flower spikes. I was not expecting the combination to be so appealing.

 The row closest to the street has green and white plectranthus, and white petunias, alternating.  The plectranthus has thick juicy leaves, so this plant is fairly well suited for drier conditions. Petunias, once established like the heat, and moderate water. The plectranthus is already cascading over the edge of the boxes, and hopefully the petunias will grow and ride the wave of plectranthus. We usually have our first hard frost late in October, which means we have almost 3 months more time to go with this planting.

It is easy to see in this picture that white flowers have the best visibility of any color in the landscape. That white will help to draw attention to the cloud of seed heads behind them. The salvia is tough to see from the ground, but it does read as a pale heliotrope blue haze.

The plectranthus is beginning to wind its way into the grass. We will edit that, if it seems to be smothering its neighbors. I do not anticipate much of that, as the front of the boxes faces south. But there will come a point where we let it all go, and watch what results from nature’s free for all. The 4th quarter of a container planting can be its most interesting phase. Once a planting reaches its mature size, its overall shape will have a sculptural element, in addition to the color and texture.

This may not be the most showy of my roof box plantings, but it is most certainly my favorite ever.  I like how loose and informal it is. I love the color. I have David to thank for these pictures up on the roof-I do not go up there. Climbing up to the roof of the Works on an extension ladder is not for me.  How it looks in these photographs makes me think I may want to bring this scheme downstairs somewhere.

There is something about this that makes me glad to be a gardener. And appreciative of the opportunity to plants these boxes differently every year. I suspect Rob really likes them too.    the roof boxes



  1. April Clarke says

    Love the grass, never tried it. Curious if the grass makes it thru winter to spring

    • Deborah Silver says

      Dear April, I had never tried it before either. I would not leave them in the boxes all winter-I will do something different next year. I probably will pot them, and winter them over inside our landscape building. all the best, Deborah

  2. I love this combination. Thanks for sharing these birds-eye views.

  3. This is one of the most stunning combinations I have ever seen! Thank you so much for sharing it with this gardener in DC!
    Totally empathize with the challenge of photos on the roof top….aerial snaps with a small drone?
    Thanks again for the glimpse of gardening in Detroit.

  4. Sandy Boylston says

    Please post a picture from street level so we can see how pretty this combination is from the ground.

  5. This is an exciting combination Deborah, and I’m going to have to try this grass (if I can find it!).
    Would love to see how it looks from down below. I’m only 3 hours away in Ohio, and this just might be the reason to make my long promised trip up to visit your garden store.
    Thanks for sharing. 🙂

  6. laurie cousart says

    love this! What are those wonderful grasses?

    • Deborah Silver says

      Dear Laurie, there is a lot of info on this grass in the post-and a link to more info. best, Deborah

  7. I have tried to grow Blonde Ambition in my southwestern MN zone 4b area, planted in the ground, and it dies away over the course of 2-3 years even though it is supposed to be hardy. Has anyone had different luck than I in a zone 4 in ground planting of this?

    • Deborah Silver says

      Dear Jennifer, hardiness involves a lot of factors-not just average winter temperatures. I doubt this grass would tolerate wet heavy clay soil, or shade. I would read up on exactly what conditions they like, and try to find a spot that is a good fit. Or perhaps it died from something not related to hardiness.I often wish that plants could talk, so they could tell me what hurts! best, Deborah

  8. Michaele Anderson says

    What a great container grouping…it manages to be fresh, fun, frothy and frilly. I love the contribution each plant makes to the over impression. Count me a fan!

    • Deborah Silver says

      Dear Michaele, love your phrase: “fresh, fun, frothy and frilly.” Thanks for this. You said it best. regards, Deborah

  9. Ann Taylor says

    You have taken rooftop gardening to a whole new wonderful level with this meadow look!

    • Deborah Silver says

      Dear Ann, I do like short meadows in confined spaces.I was not expecting to like this so much, but I do. all the best, Deborah

  10. Pat Ferguson says

    When I opened your newsletter and saw UP ON THE ROOF….it made me think of the James Taylor song!
    Once again you have outdone yourself….STUNNING!


    • Deborah Silver says

      Dear Pat, you must be younger than I am. The song “Up On The Roof” was released by the Drifters in 1962. OK, I was only 12, but I vividly remember this song. best regards, Deborah

  11. Regina M. Neal says

    Is there a white petunia in the Vista Series? Are there any other self-cleaning white petunias?

    • Deborah Silver says

      Dear Regina, I do not know the answer to this. The whitest Vista petunia is vista mini silver. When I plant petunias, I let them go. I do not dead head them. Regularly, I trim the long straggly trailers to encourage a compact and densely blooming plant. best regards, Deborah

  12. Everyone else has already done a better job than I ever could to express how wonderful this arrangement is. I’m totally into the meadow or informal look right now and the airiness of that grass is divine. Very pretty!

  13. Silvia Weber says

    Love this planting. Glad to hear you’re not traveling “Up on the Roof”, (definitely) by the Drifters.

  14. Don’t have to be an oldster to recognize “Blond Ambition” hearkens back to the Madonna World Tour days! -carol

  15. Beautiful, would love to see a picture from the storefront.

  16. I saw this grass used in the Denver Botanical Garden recently. It is lovely. I may try it here in the southeast, if I can find it. But it may have to be in a pot that is not filled with clay soil.

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