Nitrogen Fixing Trees in Our Food Forest
Most mediterranean climate soils contain very little nutrients and organic matter. Producing your own nutrients, especially nitrogen, on your land helps tremendously with helping your food forest thrive.
Why is Nitrogen Important for Plants?
Nitrogen is a primary nutrient that is essential for strong, robust and healthy plant growth.
Plants need a lot of it.
But… because nitrogen largely exists in the atmosphere, most plants can’t access it.
The good news is that you can bring that atmospheric nitrogen “down to earth” by growing nitrogen-fixing plants, such as the mediterranean nitrogen-fixing trees I describe in this article.
These nitrogen-fixing trees can use atmospheric nitrogen for their own purpose and “fix” nitrogen in the soil with the help of bacteria.
Nitrogen-fixing trees usually have deep roots, which allow them to access nutrients in subsoil layers and stabilizes the soil.
While the trees constantly growing and dropping dead leaves, they add organic matter to the soil while creating channels for aeration, which in turn support more plants.
Most species of nitrogen-fixing trees also produce useful harvests and functions, including food, wind protection, shade, animal fodder, fire wood, living fence, and timber, in addition to providing nitrogen to the system.
How to Use Nitrogen Fixing Trees
- Plant nitrogen-fixing trees in your food forest to feed nearby fruit or nut trees.
- Prune these trees regularly and use the cuttings as mulch around fruit trees and perennials to feed the soil from above.
- Compost the cuttings to create a rich soil amendment for vegetable gardens.
These are our favorite mediterranean nitrogen fixing trees:
Carob (Ceratonia siliqua)
Traditionally, carob pulp has been used for food: roasted and eaten as a snack, roasted and ground to make a cocoa substitute, fermented to make alcohol, or diluted to make carob syrup.
Carob trees also provide a wood used for making utensils and slow-burning charcoal.
While previously not believed to be a nitrogen-fixing tree, carob trees have been identified lately with nodules containing bacteria believed to be from the Rhizobium genus – which earns it the place in our list of mediterranean nitrogen-fixing trees.
Sweet Acacia (Acacia farnesiana)
A beautiful nitrogen-fixing tree with sweet smelling, bright yellow flowers used in French perfumes and a favorite of our honeybees and other pollinators.
Coojong (Acacia saligna)
A small and very productive nitrogen-fixing tree that produces every year a large quantity of woody biomass.
We use the branches, twigs and leaves for mulching and the thicker branches as firewood.
But our mediterranean nitrogen-fixer tree star is…
Tagasaste (Chamaecytisus palmensis)
Tagasaste (or Tree Lucerne) is an indigenous small nitrogen-fixing legume tree from La Palma (Canary Island).
White flowers appear in the end of winter and spring. The flowers develop into flattened pods about 5 cm long, containing about 10 seeds.
Tagasaste tick almost all the boxes as a multipurpose tree.
Except feeding us, it can be used for almost anything:
Agroforestry
As tagasaste is a deep-rooting perennial, it taps
nutrients in the subsoil and transport these to the
topsoil in the form of dropped leaves and twigs.
This and nitrogen fixing are the reasons why we plant tagasaste everywhere in our food forest.
Bee forage
Tagasaste provides valuable nectar and honey in late winter when our bees have very little flowers to forage.
Learn more about our mediterranean bee plants.
Fodder
Currently, the main use of tagasaste is fodder for livestock and it is comparable to pasture and hay.
Our chicken devour the tagasaste leaves.
Shelter
Mature tagasaste trees provide good shade and, if grown in closely planted hedgerows, create an excellent windbreak.
We plant a circle of tagasaste plants around a wind-sensitive young tree (e.g. walnut), and remove the shelter plants after a few years.
Timber
Tagasaste timber is quite dense and suitable for
manufacturing small objects.
We use the thicker branches for firewood.
Conservation and reclamation
The ease with which tagasaste can be established and its rapid growth rate make it an extremely valuable plant for revegetating eroded areas.
Landscaping
And last, but not least. tagasaste is a beautiful evergreen tree with and masses of white flowers.
Find out more about the amazing nitrogen fixing tagasaste…
I’d love to learn from you…
What mediterranean nitrogen fixing trees do you “employ” in your own garden or food forest.
Hi Jonathen,
I am creating a permaculture homestead in Catalonia just north of Barcelona.
I have been searching all over the internet to find Tagasaste seeds but have no luck.
Do you know where I might be able to find some?
Many Thanks
Olivia