ARTICLE BY: LOREE BOHL

Loree Bohl is an HPSO Board Member and the lady behind the blog Danger Garden, she’s a freelance garden writer and a spiky plant lover who grows desert loving plants here in Oregon. This article originally appeared in the Rock Garden Quarterly, the journal of the North American Rock Gardening Society, it is republished here with their permission.

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Summers in Portland, Oregon, are the stunning reward for our long, wet, grey and cool winters. Summer days are sunny and the weather is warm (some would say hot, and after the temperature records set this last summer I would agree). While many think of the Pacific Northwest as “rainy all the time” that’s simply not true. Our modified Mediterranean climate means the rains typically end sometime in May or June and don’t return until October or November.

Our sunny patio is where I like to spend summer days, surrounded by my (now substantial) collection of potted plants; agaves, aloes, yucca, mangaves, assorted cactus, and more. My husband, Andrew, is not a sun-lover however, and knowing it would be years before our Magnolia macrophylla grew tall enough to cast shade, he designed a structure to provide it. Originally dubbed the “shade shack” — because it’s so much fun to say — the name was upgraded to “shade pavilion” once complete, it was just too well designed to call it a shack.

The first winter with the shade pavilion (2009) I decided to move some of my dry-loving container plants under it, rather than into the dark garage. The tall, angled, roofline wasn’t meant to keep things below dry, but unless a strong wind came through there was a small patch of ground significantly drier than the surrounding area. We dedicated gardeners take advantage of every opportunity to keep our treasured plants healthy.

Plants huddled in hopes of staying dry

Seeing the containers huddled under cover got my husband’s creative, problem-solving, mind working. He developed a modular design that would turn the shade pavilion into an enclosed greenhouse of sorts. Our main goal was to keep temperature hardy succulents dry (cold is fine, cold and wet is the kiss of death), but I soon realized a small heater might help keep the temperature from plummeting as well, slightly increasing the range of plants I could successfully overwinter.

Those of you living in colder parts of the country might think someone in USDA Zone 8 shouldn’t complain about winter cold, but I also have an extreme case of zonal denial, I’m always pushing the boundaries of what I can grow. Plus, when you’re growing plants in containers, 14ᵒ F night-time lows and extended daytime highs below freezing — which does happen here — can allow roots to freeze and otherwise zone-hardy plants may perish.

The first iteration of the shade pavilion greenhouse (SPG) — which went up in October of 2010 — involved ends made of rigid corrugated plastic panels, with sides and a top of heavyweight plastic sheeting, draped over PVC pipe. The edges of the plastic sheeting were snapped into metal channels designed for just such a thing. Since the greenhouse roof was under the existing metal roof we didn’t have to worry about snow or ice load. It wasn’t pretty, but it did the job.

That first design went up each fall, and down each spring, for three years — until Andrew decided he’d had enough of the plastic sheeting and needed to improve upon it.

Version 2.0, which debuted in the fall of 2013, is made entirely of corrugated plastic panels sandwiched, top and bottom, between two pieces of wood, which screw together to hold the panels in place. The entire greenhouse structure is built off of eight 2×4’s which slip into place over the shade pavilion’s existing bolts, no screws or nails that mar the existing structure. Nothing that — once the walls are down — indicates this is anything but a summer-use structure. That’s the genius of the design, in my opinion.

The design does have a few less-than-ideal elements however, all easily solvable, but ones that make the SPG look a little “unpolished”. For one, as the plastic panels overlap each other they do gap a bit, so we tape them — front and back — with no-residue duct tape. There are also small gaps at the top corners that we fill with bits of insulation to keep heat in. The bottom of the rigid plastic panels need something to seal them against the gravel and paver “floor”, so we slip them into long pieces of pipe insulation.

The cement block and wood shelving is another down-market solution, but it persists mainly because it’s easy to break down and store, it’s customizable, and it can overcome the uneven floor surface of gravel and concrete pavers in a way that something solid wouldn’t be able to. The design snob in me isn’t bothered by any of these elements because the SPG happens to be situated behind our garage, hidden from the house and only seen if one walks completely into the garden and down to the patio, something I don’t often do in the winter, unless I’m checking on the plants.

The plants…that’s what it’s all about right? So far, the only losses I’ve suffered in the SPG are things I let get too dry, like a several year-old Grevillea ‘Peaches and Cream’. As noted, the original idea was a structure which would house xeric plants that need to be kept out of the winter rain, and only get a single intentional watering, or two, over the winter. Plants like Agave victoriae-reginae, A. franzosinii and A. ‘Mateo’ come to mind, as well as Aloe Saponaria and A. striatula. However, being a plant lover — some might even say collector —plants that use the space as an actual greenhouse, appreciating the slightly warmer and protected conditions, have infiltrated the mix. These need some winter water, something I tend forget. By grouping the thirstier things right by the door I’ve gotten better at keeping them hydrated. A weekly check-up is all they ask, with water distributed as needed.

January 2017

I’m thrilled to have kept an Adenanthos sericeus (coastal woollybush) alive over five winters now, this will be its sixth (knocking on wood as I type). My Sonchus canariensis, the Canary Island “tree dandelion”, actually goes dormant in our summertime heat, so it often looks its best while it’s in the SPG.

One of the rarest plants (at least in my part of the world) currently winter-housed in the SPG is a Strobilanthes gossypinus, aka pewter bush. Like plants in Proteaceae family the Strobilanthes does not react well to overwintering indoors (yes, there’s another entire garden in our basement over the winter months), so it stays in the SPG and is whisked into the basement only when arctic air arrives, and then returned outdoors as soon as possible. This year I’ll also be keeping a pair of containerized Bukiniczia cabulica under its cover. I’ve planted out a trio in the garden, but knowing they like it dry, and bloom in their second summer, I’m treating the SPG plants as insurance.

Version 3.0, under construction

I’m thrilled to report that as I write this story, Andrew had started designing, and building, SPG 3.0. The summer storage of version 2.0 had always been an issue, he hated that it didn’t break down even further. Plus, there was room for improvement on the insulating capabilities of the single wall corrugated plastic, the new design features double-wall polycarbonate panels with air pockets between the two walls. The panels are also easier to work with (not as floppy or brittle) and connect to each other with metal channels, no more duct tape! The upgraded design also includes doors on both ends, which improves air-flow and accessibility — important when you’ve packed the space full of plants.

Here are a few of Loree’s blog posts on the building of the shade pavilion greenhouse, including the “big reveal” of the latest version at the bottom:
– Version 1.0 goes up in 2010
– Version 2.0 in 2013
– A step-by-step view of the transition from shade pavilion to greenhouse in 2017
– Version 3.0 in 2018