Friday, March 25, 2011

Snowplows and Roadside Plantings, a Case for Native Annuals

Last week I did the spring clean-up of a roadside bed I designed. The plants used were all Eastern North American species.  As I was working I was reflecting on what did and did not work well. For the most part it has been doing quite well with little input from me. Up away from the main traffic flow Aronia (Aronia arbutifolia), Meadowsweet (Spiraea latifolia) and Shrubby Cinquefoil (Potentilla fruticosa) are growing well as are the perennials including Prairie Aster (Symphyotrichum turbinellum), Purple Coneflower (Echinacea purpurea), Appalachian Blazing Star (Liatris squarrulosa), Stiff Goldenrod (Solidago rigida), Red Columbine (Aquilega canadensis) and my favorite grass, Prairie Dropseed (Sporobolus heterolepis).

When I designed this roadside bed back in 2006, I selected plants that I thought would withstand drought conditions, salt spray, full sun and wind. The one aspect that I had not fully appreciated was tolerance to disturbance, particularly resistance to snow plows! Where the bed is protected by a curb there is not much of an issue, but down near the highway the surface of the bed is often scraped over, either directly by the plows or as a result of snow being pushed up and over the sidewalk.
When I first learned that blueberries were salt tolerant I happily incorporated them into the roadside position.  I thought people going by would be impressed at how versatile of a shrub blueberries were. I was shocked the following spring when I found the bushes pushed nearly a foot further into the bed, the result of plowing of the snow. Well, the plants are still there 4 years later, but just hanging by a thread. This is obviously the wrong place for what would otherwise be the right plant.

Problem area, after a fresh layer of leaf mulch. 
The blueberry twigs are still in there.

Down by the road Seaside Goldenrod, Solidago sempervirens, is performing well. In fact, this is an example of a native species that is expanding into the urban environment in disturbed areas where road salt makes it difficult for other species to establish. The Prairie Dropseed in this area (those that haven’t been plowed over) are not doing as well. However, Sand Love Grass, Eragrostis trichodes, a new addition to this area does seem to be doing better.

Considering the conditions at this end of the planting I really need a plant (or plants) that will have a continued presence despite a nearly annual scraping of the top layer of soil. Use of a native annual, or perennial, that vigorously self-seeds should fit the bill. Since the plant starts each year anew, disruption of the crown and roots would not be an issue.

This year I have seeded in some American Pennyroyal, Hedeoma pulegioides, a true annual that grows in dry disturbed locations and produces a lot of seed. I also added seeds for a couple of perennials, Spotted Beebalm, Monarda punctata, and Butterfly Weed, Asclepias tuberosa, that are known to reseed effectively and have some salt resistance. By starting from seed I am testing whether this site has the right conditions for germination, a critical factor if they are to get established there.

To get some new ideas I turned to the Advanced Search  function on the USDA Plants database. Here I looked for plants that will tolerate full-sun, drought and salt. While not every plant in the database is searchable in this way, it can provide many leads. Among the results was the Seaside Goldenrod that is already thriving there. A new lead that was generated was Beach Sunflower, Helianthus debilis. I’ve been growing this from seed in pots at home for a couple of years, now it’s time to put it to the test in the field!


Laurrie said...

I have the same problem in microcosm, as the snowplows tear up anything near my driveway, including, of course, any sod that edges it. This is quite the experiment in your roadside planting! I was surprised about blueberries being salt tolerant, that seems counter-intuitive to their need for acid conditions, so it's good to know.

Curbstone Valley Farm said...

We're fortunate not to have to deal with snowplows here, but when I was designing my Mother's garden on the east coast, it was very much a consideration. I finally understood my so many gardens are merely lawn where the property meets the road there. She had an almost 6 foot snowbank to contend with this winter, and if we'd planted anything shrubby there, I'm sure it would have been long gone. Annuals make perfect sense for such a space.