Permaculture Essentials: Nitrogen-Fixing Plants

The need for a source of nitrogen in a permaculture garden is important, because the goal is often to eliminate the use of any chemical fertilizers. As a result, permaculture enthusiasts have come up with many ways to keep their soil rich and fertile without the use of chemical additives.

Planting nitrogen-fixing plants in between or even underneath the fruit trees and berry bushes can help replace nitrogen that the plants use up in the soil. Nitrogen-fixing plants have nodules on their roots that are actually large colonies of bacteria. These bacteria use nitrogen gas from the air and transform it into forms that are useful to plants.

Legumes are the most common family of nitrogen-fixing plants. Simple pole beans or pea plants can be planted underneath fruit trees and allowed to grow using the tree as a trellis. They will provide the tree with nitrogen, and quite possibly provide food to the gardener. There are also many nitrogen-fixers that are tree-sized, so they will provide much more nitrogen to the soil than a couple bean plants. When one of these trees reaches a certain height, you can chop off the top, use the branches as nitrogen-rich mulch around a fruit tree, and the roots will shrink and release nitrogen into the surrounding soil.

Composting can also keep the soil very fertile. Kitchen scraps and yard waste can be combined in any type of bin, or even just a pile, and will eventually result in rich, dark compost to spread around the permaculture plot. It is important to turn the compost periodically, because the breakdown on the materials requires oxygen, so it will take much longer if you do not turn it.

Coffee grounds are found to be high in nitrogen, so they can also be used to enrich the soil. Coffee grounds and filters can be added to compost piles, or you can just sprinkle the used coffee grounds directly onto the soil. Acid-loving plants such as blueberries can also benefit from the acidity of the coffee grounds.

A somewhat strange way of returning nitrogen to the soil is by using human urine. This is actually used by many permaculturists and gardeners as a great fertilizer. It is recommended that you use 1 part urine to 6 or 8 parts water, otherwise the ammonia in the urine can actually be strong enough to burn the plants. One reason this hasn't really taken off yet is the question of where to store urine in the house. Jugs full of urine might be a little unsightly to guests. Maybe next time you have to go, instead of walking to the bathroom, walk out to the garden instead.