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Those balls on roots are Nitrogen fixing root nodules.
Nitrogen fixing root nodules transform environmental nitrogen into nitrogen for the soil. And, by adding nitrogen to the soil, this provides a key nutrient to plant roots.
But, that’s a pretty big oversimplification. Still, this symbiotic work between plants, bacteria, and soil is a great way to easily help your garden. And, its inexpensive!
So, why do beans grow root nodules?
The nitrogen fixing root nodules aren’t exactly part of the bean plant. Instead, they are actually the home for a bacterium that works symbiotically to exchange carbohydrates from the plant for the bacterium for ammonium for the plant from the bacterium.
If you want to go deeper into this science, you can read more here.
Are green beans the only plants that have this ability?
Green beans are one of many plants that are well known for doing nitrogen fixation. And they do this work in tiny bean-like nodules in their roots. However, there are many other plants that are called nitrogen fixers.
For instance, all plants in the bean family do this. This means trees like golden chain trees (Laburnum) can fix nitrogen and improve the soil around them. As well, some weeds like stinging nettle and lawn clovers can improve soil this way.In fact, many farmers grow red clover to intentionally improve soil through the plant’s nitrogen fixation properties.
Even our forest of indigenous alder trees is being improved by the forest’s nitrogen fixing properties (as well as all the organic debris they add to the soil.)
So, how can home gardeners encourage nitrogen fixation?
Like farmers, home gardeners can use cover crops for nitrogen fixation. And, just to be clear, nitrogen is one of the most important nutrients plants need for their systems.
Too be clear, this doesn’t feed plants; plants feed themselves. But they need the right balance of nutrients in order to thrive.
So, planting cover crops like red clover and fava beans may help improve your vegetable garden soil. And, allowing clover to thrive in your lawn will help provide nitrogen to grass, which needs a lot of that nutrient. Plus, choosing nitrogen fixing trees can help improve ornamental garden beds. Moreover, allowing weeds like nettles to have a place in your garden can enrich soil with bountiful nitrogen too.
Soil health is key to helping our gardens thrive.
Learning about nitrogen fixation reminds us that soil is alive. And the relationship between the bacteria, fungi and plant roots that live there is complex. Nitrogen fixation simply is symbiosis at work in the soil.
And, there are fungi living in the soil that work with plant roots to share carbohydrates (from plant to fungus). And, this happens in exchange for water and soil nutrients (from fungus to plants).
Simply put: what goes on in our gardens below the soil is key to our garden’s success. So, 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 to box and sell.
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Plants and their soil buddies have formed amazing alliances.
Plants and their allies can care for themselves without human interference. They already know how to team up to gather nitrogen to grow. And they work together to share carbohydrates and water. So, odds are they’ll out-wit humanity’s short-term attempt to cultivate nature.
And that’s a good thing because over-applied, lab-crafted chemical fertilization can lead to an array of soil problems. These may include poisoning water supplies and creating soil chemistry imbalances. And more.
You can check how active the nodules are by splitting them open. If the nodules are red to dark red they are active. If they are light pink to white then the rhizobia are not active and not fixing significant amounts of Nitrogen
Thanks for sharing Brett. This is fascinating stuff!!
Simply grow peas on the ground where beans grew and leave the bean roots alone as you dig.
The results are amazing
Chris, thanks for chiming in. Generally, it’s a good idea to NOT plant beans in a spot where peas were just grown. Instead best practices suggest planting something outside the legume family. This helps break lifecycles for pests and disease that might otherwise become problematic for these crops.
thanks – are nettle nitrogen fixing or applies as a tea?
Laurisa, Thanks for your question, but before we answer can you clarify what you’re asking? I’m not sure what “applies as a tea?” is querying. Thanks!