In a few spots in my garden, I wonder if I might have too many architectural plants together for them to have individual impact. I think of it kind of like having a roomful of divas; while it may work just fine when VH1 puts together a concert... well, imagine having them live together in a garden, with each constantly trying to outsing the others!
In other places, I am very aware that a nice architectural plant is badly needed to add some kind of structure, or focal point. The term "architectural plant" typically refers to a plant that is evergreen (or at least woody, as in shrubs and trees) and provides year-round interest. In this picture, the Japanese maple would technically be the architectural plant in the composition:
But in the above picture, it's the Spanish foxglove (digitalis parviflora) that I find so architectural right now. When I talk about "architectural plants," I suppose that I really mean plants with some special textural interest. With everything else being so fine-textured and soft/mounded in form, the rigid spires of foxglove really add interest in the picture above; hence I think of them as my architectural plant in this little area.
I do use a lot of leaf color, but I don't think that color really lends itself to designating a plant as "architectural" as much as texture and form does. For example, in this little vignette below, my purple 'Regina' heuchera is the odd man out in terms of color--and yes, that does make it "pop." But if I had to pick an architectural plant in this picture, I'd choose the 'Sioux Blue' sorghum grass for its upright, strongly vertical form... even though it matches the horehound plants that flank it in color:
In a single area, different plants might hold the architectural limelight when the garden is viewed from different angles. In the picture below, the foxgloves are still pretty (especially since they pick up the orange color in the heuchera, and are set off by the blue of the catmint behind) but what really grabs my attention is the 'Northern Halo' hosta. Its chunky leaves make a nice counterpoint to the lacey Japanese maple leaves, as well as the lamium and golden oregano used as groundcovers at its feet:
And sometimes, the architectural plant in a bed counts as such for me because of its effect en masse. An individual drumstick allium wouldn't be able to hold a candle to the 'Northern Halo' hosta architecturally. But dozens of them waving at waist height add a much-needed focal point to my little "prairie garden" of butterfly weeds, baptisia and grasses:
(By the way, I have decided that drumstick alliums are one of the hardest plants to photograph. After many, many attempts I have yet to really capture their presence on camera... they are simply stunning in their elegance and simplicity, and before they shoot up and tower like lolipops hoisted above the baptisia, this little garden looks like little more than a weedy patch of wildflowers.)
So while all plants have color, and texture, and form... the "architectural" plants as I think of them are the ones that have that extra something. That je ne sais quoi, that elevates a plant combination beyond the normal into the sublime.
I'm sure that everyone has their own thoughts on which plants fit this kind of description, since matters of taste in the garden, as in art, are so personal. And I'd love to hear some of your thoughts, especially since I'm searching for one such plant to use in my currant bed!