10 Mile Interchange Hellstrip

Fitter, happier
Am I the only one who finds this repeating motif on the new(ish) Ten Mile Interchange just a bit creepy?

Aside from the undertones of Orwellian Maoist thought control, The Ten Mile Road Interchange in Meridian, Idaho represents a subtle change in public works projects around Ada County. Gone are the days of shoulder to shoulder asphalt and concrete. Honest to goodness, live plant material and permeable surfaces are beginning to be incorporated into new design.

But, as I was often reminded as a child, they don't give you a medal for good intentions, so let's perform some taxpayer deconstruction of the project.


Behold, an Idaho winter: a washed out/monochromatic sky meets a washed out/monochromatic planting bed.

What? I'm not being fair because it's February? While it is true that last summer there was a lovely succession of color here, compliments of Echinacea purpurea, Coreopsis verticillata, Perovskia atriplicifolia, Gaillardia, and Leucanthemum x superbum, they are all now distant herbaceous memories from a half forgotten warm season.

Winter "structure" is mostly provided now by the skeletons of miniature Berberis, the carcasses of winter kill Lavendula, prematurely trimmed ornamental grasses, and the much maligned Yucca filamentosa.

(Incidentally, I swear I will punch the next person who tells me that "there's a reason they call them YUCKas". I mean, cut them a little slack, they are the only plants in this bed providing any real color for five months of the year!)

I think lavender is great and I probably overuse it in my designs, but what is there not to like? It's mildly drought tolerant, the bees love it, it smells terrific and it blooms for months.

There are plenty of varieties of  lavender that are dependably hardy in our area, but I'll be surprised if even half the lavender in these beds wake up in the spring. They really don't catch a break between the basalt "mulch" heat sink in the summer and snow plows and drunk drivers in the winter.

Which leads us to...


Un-shaded asphalt surfaces can reach temperatures as high as 160 degrees. A planting bed surrounded on all sides by asphalt and concrete receives a tremendous amount of this as reflective heat. What is the logic of using dark, basalt mulch in the beds to further heat up the poor plants?

Crushed basalt is also a nightmare to maintain.

Another observation: the median beds are elevated, surrounded by slope faced curbs. Perhaps a better approach would have been to match the planting grade with that of the road and install curb cuts for passive rain harvesting?


The purple cap on the popup gives us the heads up that non-potable water is being used. In many areas of the country that means reclaimed, grey water with potential problems associated with salt build up. Not here. Snow melt is what built Boise and our urban forest and I'm so pleased to see it being used in place of domestic water.

As a card carrying member of the "green industry" I'm expected to hate broadcast sprayers and embrace drip lines and micro-irrigation, but too often micro-irrigation = dead plants. This is partially due to incorrect installation (single emitters rather than grid installation), but also because our soil has lousy capillary action resulting in uneven distribution of water and poor root development.


There's a lot to like about this project- for about 8 months of the year anyway. Swapping out even half of the standard army-green Yucca filamentosa with a variegated form (Yucca filamentosa 'Bright Edge' or 'Color Guard'), or the bluish Yucca rostrata would give this planting a lot more punch during our indeterminable "gray season".

The damaged lavender along the edges of the median strip should probably be replaced with a tougher, semi-evergreen perennial that can take the heat and drive-over damage; maybe Penstemon pinifolius or Arenaria 'Wallowa Mountains'?

Since I'm feeling generous, I'll say that the crushed basalt "mulch" is slightly better than paving over a garden bed.  I'd really like to see an organic mulch installed (or at least light colored, porous sandstone if you must have rock). I'm sure the crushed basalt was installed out of an assumption that an organic mulch would blow out onto the street and the rock would stay put. You can see how well that's working.