The Walden Effect: Farming, simple living, permaculture, and invention.

Nitrogen fixation in the forest garden

Mimosa forest gardenToensmeier didn't only report on his own forest garden in Paradise Lot; he also included tidbits he'd seen in others' gardens around the world.  In his experience, forest gardeners tend to follow one of three main methods of incorporating nitrogen-fixing plants into forest gardens.

The first method is typified by Martin Crawford's forest garden in England.  Crawford includes a tall, open canopy of nitrogen-fixing plants, which in his case is primarily high-pruned alders.  Toensmeier mimicked this technique on a small scale by using a mimosa tree as a nitrogen-fixing canopy species, but he wasn't very interested in using up much of his small backyard with nitrogen-fixing trees.

Another method that works well in extensive forest gardens is to alternate nitrogen-fixing trees with food-producing trees.  In general, Toensmeier wrote, gardeners tend to alternate two or three edibles with one nitrogen-fixer.  Of course, space constraints again make this approach problematic for the urban gardener.

Forest gardenThe final technique, which is what Toensmeier mostly follows, is to use Geoff Lawton's chop-and-drop method of coppicing nitrogen-fixing trees and shrubs.  Toensmeier also includes a lot of nitrogen-fixers in the groundcover category, notably hog peanut, licorice milk vetch, and groundnut, although these vigorous plants do outcompete some preferred species.  Foot-tolerant groundcovers like clovers and prostrate birdsfoot trefoil in the pathways can also help bring nitrogen into the system.

I'm less of a nitrogen-cycling purist than many permaculture advocates, and I have to admit that if I had a only a tenth of an acre, I'd devote the whole acreage to edibles and bring in my nitrogen as manure or compost.  Even Toensmeier admits at the end of his book that the forest-gardening dream of a do-nothing paradise is unrealistic, and if you're going to have to nurture the garden anyway, why not topdress a little manure from your rabbit hutch or chicken coop?

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This post is part of our Paradise Lot lunchtime series.  Read all of the entries:

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About us: Anna Hess and Mark Hamilton spent over a decade living self-sufficiently in the mountains of Virginia before moving north to start over from scratch in the foothills of Ohio. They've experimented with permaculture, no-till gardening, trailersteading, home-based microbusinesses and much more, writing about their adventures in both blogs and books.

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or just let a few roam freely! Like a permie guy does here in hawaii. He has boxes close to his open patio for the chickens to lay eggs in and he opens the boxes from inside his house next to kitchen. meanwhile the ground cover is planted in perenial peanut and the chickens run free.

Comment by jon kirby Tue Mar 12 02:47:37 2013

As I was reading, I was mentally preparing to add a comment about keeping meat rabbits and using their manure as a nitrogen source. Then I got to your last sentence :-).

If you're growing lots of biomass (coppicing fodder trees, rye/vetch/oats, corn, bamboo, banna grass, sugar cane, vegetable prunings, etc) you'd have a lot to give to the rabbits, cutting down on their feed costs. It's also much faster to cycle biomass through an animal than to compost it. Lastly, rabbit manure is a perfect fertiliser - it comes right out already pelletised, and it's "cool" so can go straight into garden beds (unlike "hot" manures like chicken or cow).

Comment by Darren (Green Change) Tue Nov 12 16:37:34 2013

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