Vertical Gardening at -7 F

I've been working on compiling a list of tough natives and climate adapted species that could survive in a vertical garden application through our Boise winter with little or no care. In May, I was commissioned to build my first "xeric" vertical garden, so I used this opportunity to try out both drought AND cold tolerant plant varieties. 

Although I'm very interested to see how true Idaho natives like Eriogonum (Buckwheat) would do in a vertical installation, I settled on cultivated plants that are pretty easy to find in Boise nurseries: Hemerocallis 'Double Moses Fire' , Nepeta 'Walker's Low' , Artemisia 'Powis Castle' , Yucca, Sedum and Stachys byzantina 'Helene Von Stein'. 

The first pic shows the wall right after it was installed at the end of May. The second shows growth after the first six weeks. 

In a classic case of be careful of what you wish for, I was hoping we'd have a real winter here in Boise this year so I could get a true sense of the durability of these plants. 

My wish has been granted.

I snapped some pics of the wall a few days ago after we'd dropped convincingly below zero more than once.

Alive, but looking pretty freeze dried. The Artemisia, Stachys and Yucca are bravely continuing to provide evergrey winter interest, but everything else has pretty much given up.

Some closeups...

Tough-as-nails Lamb's Ear (Stachys byzantina) still hanging in there.

Sedum tetractinum looking a lot like the frozen grapes my mother fed me as a kid. Artemisia 'Powis Castle' taking the frigid weather in stride.

Yucca rostrata 'Sapphire Skies' looking exactly the same as the day I planted it.

We'll see how things are looking in February and then again in May. 

I'd love to get any xeric/cold hardy plant suggestions for vertical applications!