Hello, I'm planning a green wall for the front façade of a building in Bellingham, WA. It will be covered with a stainless steel cable training system made by jakob (www.jakob.ch has some information if anyone is curious). I'm seeking some opinions on what to plant in a long planter on the roof that runs the length of the wall (so the climbers will be climbing down, not up) and a smaller planter at the base of the wall. Research so far has led me to the following: Winter jasmine (Jasminum polyanthum), Blue crown passion flower (Passiflora caerulea) and the evergreen Clematis (Clematis armandii). I need relatively fast-growing evergreens to cover the wall. I was thinking it might be nice to plant some annuals such as Black-eyed susan vine (Thunbergia alata) for seasonal interest. Does anyone have experience with these species in the northwest? Other suggestions on good climbers that are aesthetically pleasing? I know about Japanese honeysuckle (Lonicera japonica), but it seems like an invasive pest (although it doesn't appear on Washington's noxious weeds list), so I'm inclined to steer away from it. And oh yeah, no ivy or anything else too woody... Thanks!
How big is the planter? The clematis will probably freeze out eventually unless the planter is big enough to provide enough soil to prevent root loss. It can freeze back even in the ground during hard winters. The passion vine is quite likely to have problems with cold injury perched up in the air in Bellingham. It tends to be grown against warm walls even in Seattle, although there are some nice ones on a fence at the Wells nursery farm near Mt Vernon. North winds must come across an expanse of open field and blast through the planting site in winter. How woody is too woody? Both the jasmine and the clematis are woody, as is the honeysuckle, which is not weedy here in our summer-dry western climate. The hot, humid eastern summers suits many plants from similar east Asian climates so well they have gone wild and become choking pests. Subzero hardy. drooping species and cultivars of evergreen conifers may be your best bet. These are woody, of course. But you have to use something that will tolerate freezing of the roots, unless the planters have more volume than might be expected.
The upper planter will be 20 high and 24" front-to-back. The total length is 30', so it will probably be broken up into 4 separate planters for ease of fabrication/installation. The bottom planter is 24" high, 16" front-to-back and 4' wide. Too woody... would be something that would get too heavy and damage the training system and/or building front. For example, I walked by a mature ivy plant growing up a building yesterday and the trunks were at least 4" in diameter. What would be some examples of subzero hardy drooping species, or evergreen cultivars?
So it's not woody that is a concern so much as big. Various creeping junipers, weeping Norway spruce...visit an independent garden center with a full line of conifers. Many commonly sold ones such as those mentioned would have suitable growth habit and hardiness. Roots are much less hardy than tops, immature roots even more tender than mature roots. Plants in containers get cold coming in on three sides, once they fill them with roots the new ones end up plastered right against the walls of the container--in position to be frozen or baked as soon as cold or heat get through the walls. Planters on top of a wall will not even receive the benefit of warmth from soil underneath them. Another one that could work is kinnikinnick (Arctostaphylos uva-ursi). Subzero hardy and trailing like ivy where suspended.
Twinflower;Linnaea borealis will easily cascade down the height required, eventually. I have seen them cascade well over 30 feet.
