Perennial or shrub for elevated planter in Zone 3 - Knowledgebase Question

Idaho Falls, ID
Avatar for jhenry9
Question by jhenry9
August 26, 1999
I'm supposedly in USDA Zone 4, but I've measured lows in my yard of at least -25F every year since I moved here, so I think my microclimate must be Zone 3.

I've got a problem planter that I -want- to put some sort of permanent planting in. It's made of badly cracked and severely frost-heaved brick, about 25 feet long, 45 inches high and only 2 feet wide. It faces south, which is good, but is fully exposed to our rather wicked prevailing wind. And I can't get rid of it because it holds up my front porch. I need to plant SOMETHING in it that will cascade a little and conceal the damaged brick, at least spring to fall and preferably winter, too.

The problem appears to be that, because it's narrow and elevated, the ROOTS of whatever is planted in it not only get exposed directly to sub-zero temps, but also have to endure rapid temp changes and freeze/thaw cycles. I inherited this with the house. So far, the ONLY things surviving in it are some real happy tulips and ONE juniper which has sunk its roots all the way down into the soil beneath the planter. There are 3 stumps of junipers that didn't make it in the planter.

On the recommendation of my local nursery, I've tried snow-in-summer, silvermound, and even tried planting a clematis vine in it and letting it sprawl. All of them seemed to root well and take their first summer/fall, but died over the following winter.

Any ideas beyond some plastic ivy?

Answer from NGA
August 26, 1999
How about wooden tulips? No seriously, talk about a tough spot! The problem is not only the freeze thaw but also the fact that many plants are not root hardy at such cold soil temperatures even though their tops may be hardy in your zone. It might pay to think laterally and plant the (real) ivy or some other vine in the soil directly in front of or next to the planter so that it can crawl upward to soften the look, and then try a plant with a winter "presence" such as one of the ornamental grasses in the planter itself, knowing that those in the planter may have to be considered annuals.

Judging from the suggestions made by your local nursery I would guess the planter to be hot, sunny and very well-drained. Other plants to experiment with might be basket of gold (aurinia saxatilis), baptisia, catmint, peachleaf bellflower, bloody cranesbill (geranium sanguineum), "Cerise Queen" yarrow, purple coneflower, amsonia, and sedum "Autumn Joy". According to the book "Perennials for Dummies" by Marcia Tatroe these are able to withstand temperatures to 40 below zero and they all do well in a hot sunny well drained spot.

Finally, you might think about either widening the planter or possibly insulating it somehow. Good luck with your project!

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