Fresh-pulled Nodule-filled Green Bean Roots

I several previous posts I’ve talked about fixing nitrogen. This symbiotic work between plants, fungi and soil is a great way to easily help your garden. And, its inexpensive!

Yesterday, as I was clearing out beds of summer vegies to make way for fall plantings, including nitrogen-fixing fava beans, I pulled out spent green bean plants. Green beans provide nitrogen fixation, doing the work in tiny bean-like nodules in their roots. When I pulled the plants, so came several with well-formed nodules.

Not every nitrogen fixer has nodules, but green beans are one of them. The nodules aren’t exactly part of the plant but are actually the home for a bacterium that works symbiotically to exchanging carbs from the plant for the bacterium for ammonium for the plant from the bacterium. (You can read more here about the science of the exchange.)

Close-up of Green Bean Nodules

So, here again we see symbiosis at work in the soil. There are fungi living in the soil that work with plant roots to share carbohydrates (from plant to fungus) in exchange for water and soil nutrients (from fungus to plants). This is an important reminder that although it can be easy to forget about what goes on within our gardens below the soil, this area of a plant’s world is one of the most important. Again and again we are reminded that our investment in soil health is critical to a healthy garden. And, the relationships that have evolved among plants, fungi and animals in the soil goes beyond what humans have developed in chemical labs over the last 100 years or so. The plants and their soil buddies have formed alliances like nitrogen fixation, carbohydrate sharing and water acquisition and supply that out-wit humanity’s short-term fixes that often create long-term problems such as toxic chemical fertilization run-off poisioning water supplies. But…that’s a story for another time.

Get out there and fix some nitrogen with some cover crops for winter. A few beans will save you a bundle in nitrogen fertilizer (and related issues) down the road!