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Nitrogen is essential for plant growth, but as organic gardeners, we don’t just go get some chemical with the right N-K-P numbers, right? We could go buy some compost or steer manure, but while these can be valuable components to get our garden started, there is a more sustainable way to maintain soil fertility. Nitrogen-fixing plants can do the work for us for a fraction of the cost and while reducing our carbon footprint.
Many plants have the ability to take nitrogen, the most abundant element in the atmosphere, and fix it into the soil. These are often the plants that thrive in the worst soils: alder, indigo, clover, vetch, and Russian olive. Consequently, many are considered weeds and, in fact, can be invasive. However, by choosing varieties that are not invasive in your area and mixing them generously in your garden, over time you will create rich, nourishing soil.
Nitrogen fixing occurs when symbiotic bacteria adhere to the roots of compatible plants and form nodules containing enzymes for converting inert N2 (nitrogen gas) into usable NH3 (ammonia). Two components are needed to make this happen. First, you need a nitrogen-fixing plant; second, you need its compatible bacteria.
There are numerous plants that fix nitrogen, some of which you may already be growing. These include legumes (beans, peas, indigo, lupine, peashrub, vetch, alfalfa, clover), alder, eleagnus (autumn olive, Russian olive, goumi), and locust. It is easy to incorporate some of these into your annual and perennial gardens.
Finding the compatible bacteria can be somewhat trickier. If you have grown beans before, it is likely you already have that bacteria present. Otherwise, you can acquire the appropriate bacterial inoculant online for most legumes and clover. It is virtually impossible to find inoculants for other nitrogen fixers. However, nitrogen-fixing plants will often come already inoculated. Also, if you know someone who is successfully growing the plant you want, see if you can get a handful of dirt from near their plant and drop it in the hole when you plant your own. If you have a good mycorrhizal network in your soil (sheet mulching will help this enormously), that should help bacteria get where they need to go.
I aim to plant at least one nitrogen-fixing plant for every two other plants. It’s a difficult goal to achieve, because often the nitrogen-fixing plants do not bear the fruit we would like or look particularly attractive. However, in the long run, this will help the more desirable plants to grow more of what you really want with less effort from you. Following are some ideas for making the most of your nitrogen-fixers.
With planning, nitrogen-fixers can serve more than one purpose and be a significant contributor to your garden or food forest.
Nitrogen-fixing plants are a boon to the organic gardener, eliminating the need for importing nitrogen-rich fertilizers and reducing your carbon footprint. Try to incorporate them into your food forest by alternating edibles with nitrogen-fixers. Select nitrogen-fixers with edible or useful parts such as peashrub or Goumi berry for more utility. So often, these nourishing plants are omitted from the forest garden in the hope of growing more food, but the reverse is likely the result: the garden is less vital or requires more input from the gardener than if it had contained nitrogen-fixing plants. Plant some of these useful and beautiful plants and reap the rewards for years.
© 2018 Amelia Walker