JARS 42n4 - Roof Top Living With Rhododendrons

Roof Top Living With Rhododendrons
Susan Baker, Vancouver, B.C., Canada

Reprinted from the Vancouver Rhododendron Society newsletter

We can't see our roof garden from the living areas of our townhouse because it is the roof and access is from the inside stairway up through the skylight hatchway. I guess my only regret is not being able to enjoy the sight of the garden in all seasons, all the months of the year, but it also makes it very precious and our lives very season oriented.
My choices for plant material have evolved with experience in this rather restrictive environment, although surprisingly, not necessarily to a safer or wiser course. Any fool knows that tree rhododendrons don't belong on a 600 square foot roof garden, but we have a few anyway because I like the big leaves and the challenge.
I have bundled R. magnificum and R. macabeanum into an outer layer of extra plastic pot and stuffed the space between with dry peat moss while mulching the surface well. Both plants had survived the brutal winter of 1984-85 with less care, however, R. giganticum was lost, so I had some concern about pushing my luck without taking extra precautions.
My first plants were hybrids salvaged from the Mothers' Day selection at a corner store in Kitsilano. The blooms were gone and the foliage wasn't selling the plants, so I offered $1 each to "try my luck".
'Virginia Richards' is very grateful and far too large to move now, some six years later. I'm going to need Ken Gibson's crane to lift her off the roof and into the landscape below!
I gave 'Roseum Elegans' to my mother who has (now) an experimental cold weather rhododendron garden in Kamloops. ('Roseum Elegans' is planted in our False Creek landscape by the dozen and I lay awake nights plotting ways to replace them, with more interesting rhododendrons.)
'Vulcan', the third orphan, has seen shows, being worthy of display. He is now too big to cart up and down the stairway. He blooms reliably throughout June and is therefore a perfect roof garden plant since use of a roof garden spans May to September as the warm weather will have it.
Containers are a general pain, quite frankly. I would like to build great solid terraced constructions wherein a kind of permanence lies, but this would not allow maintenance of the roof membrane.
Frank Dorsey always greets my disconsolation over the loss of some pet plant with a cheerful "oh good, you'll have to buy more. . ." I've come to accept the losses as part of the learning curve - my fault - as the patterns of their demise become clearer.
The first few summers were without the trellis overhead and we lost plants to cooked roots (Phytophthora). Black plastic pots are cheap and almost invisible but they heat up something frightful.
Small plants that came from gardens with dense soils and didn't get repotted intelligently either soon enough or well enough, were lost in the first years. Containers must have very good drainage and also some means to maintain moisture in the soil. Therefore, we water porous containers daily in high summer, while only misting the plastic tubs.
Some plants drink volumes - like 'Temple Bells' and 'Hotei'. Neither wish to become bonsai. They get pruned vigorously every two years now to reduce the pressure to put them in the - dare I say it - ground!
I prune rhododendrons. (That gets me a black hat in the Westerns.) I like pruning plants and I think of pruning as akin to a hair cut - maybe a mite brutal for the first couple of weeks.
Container gardeners root prune as well in order to consolidate the root ball into an efficient compact support system. Pruning the foliage balances the roots and extends the container life of the plant. Remember that a respectable bonsai is into its second generation of gardeners.
Leggy specimens usually need pruning although genetic imperative will persist over cultural conditioning. Twiggy, leggy types by nature should be situated where their skinny legs/ ankles don't figure prominently unless the form is desirable as a feature.
'Lady Roseberry' is a good example of "Miss Olive Oil" in my garden. I love the flower but the plant is overwhelmed by almost anything with density and mass. She almost wants a lattice behind her so she can become a William Morris tapestry.
Roof tops are a good place for upright growing plants because they offer space around them lower down for inter-planting with pots of summer blooming annuals and perennials.
Big, broad 'Virginia Richards' takes up the space of three upright plants. If it weren't for her great foliage, I would have "grounded" her years ago.
Foliage is a big deal on the roof, foliage and late blooming time. The plant that has both is a must. I'm also sentimental about origins. If somebody gives me a plant or I rescue it or some other special association is linked to it, the plant is assured a plant in my heart. This is why I am cluttered up to here with plants (and cats and books and memorabilia). I can hardly claim to have a collection of distinction.
However, as I move towards ever more rhododendron species that seem less adaptable than many of my hybrids, the future pattern is likely to remain one of collection rather than composition. I hear Frank Dorsey telling me to "try this" and "you must have that", and laughing at the greedy expression of discovery on my face.