Sunn Hemp's Sneaky Strength
A reflection on a resilient and cheerful cover crop, and a meditation for the solar plexus
Five years ago, when I started working for the Natural Resources Conservation Service, one of my first assignments was a short USDA blog post on a University of Texas Rio Grande Valley cover crop project. It was my first introduction to sunn hemp, a resilient plant happy to grow in a variety of climates and soil types, and I was smitten.
This summer, looking around at three acres of what used to be lawn (when we bought our property, it was entirely well-manicured grass), I realized that one carefully-placed nursery pot at a time wasn’t going to do the trick if I wanted to really start to do the big work of setting the welcome mat out for bees and butterflies, rebuilding the soil, and transforming the monocrop landscape into something a lot more interesting.
So, for the first time as a home gardener, I put into practice on my own acreage what I’d learned in theory and planted some cover crops, starting with sunn hemp. A few things about this particular plant that amaze me:
It grows like a “weed.” A good thing, in this case: once raked into the soil and given a couple of weeks, my new crop took off like a rocket, rapidly shooting up one, two, and then six feet (under the right conditions it can grow up to NINE feet tall!)
It fixes nitrogen in the soil. I am not a soil scientist, and it took me a while to catch on to what was happening when “nitrogen fixing” was referenced. I thought what was happening was that these plants just keep already-existing nitrogen in place, ensuring it doesn’t run off in a rainstorm. What’s actually happening is far more interesting. I’ll let Texas A&M explain it: “bacteria [in legume roots] can take nitrogen gas from the air in the soil and transform it into ammonia (NH3) that converts to ammonium (NH4) which can be used by the plant. This ammonium is the same form as in ammonium nitrate (34-0-0) and ammonium sulfate (21-0-0) fertilizer.” Neat, right? Once growing season is over, you terminate the crop and leave it in place to decompose, returning its stored nitrogen to the soil for the next crop to use.
Its cheerful and long-lasting flowers attract pollinators. Although it seems that honeybees aren’t heavy enough to do the work of pollinating sunn hemp, they visit anyway, gathering pollen and nectar. On a random August afternoon this summer, I observed not just our farm honeybees, but several species of native bee, happily enjoying the free buffet.
Unbelievable biomass: Once I started clearing the plot this fall, things got really interesting. Above ground, I was pulling up huge amounts of plant material - enough to compete with my constant supply of downed limbs along the driveway (the one place we have big trees) as dead hedge building material. Below ground, although sunn hemp is supposed to grow a deep, strong taproot, I found that my crop hadn’t quite had the fortitude to bust through the heavy clay and had instead sent out a fine, mesh-like network of lateral roots. What had been a fortress, a forest, of yellow and green all summer gave way easily with just a light tug. As metaphors go, this feels like part inspiration and part cautionary tale: I’ll bet we all know someone who seems to have it all together, radiating enthusiasm, who could perhaps use just a little more support once you look under the surface.
In keeping with our solar plexus theme this week, I nominate sunn hemp as a source of inspiration. I considered making this a post about the braggadocios nature of my new favorite legume, all big look-at-me energy. In reality, though, all that swagger is well-earned and well-used: this is a strong, tall, confident, and sunny plant that contribes endlessly and effortlessly to the ecosystem around it. It’s also absolutely attuned to its place in the order of things, ready to release and rest at the end of the season, knowing that even the most energetic of us must eventually accept periods of stillness and quiet.
Below: a five-minute meditation for the solar plexus, and the audio version of this post.
Meditation:
Post audio: