Mediterranean Nitrogen Fixing Trees

I could use some help...

In our hot and dry mediterranean food forest in Tenerife (Canary Island) we are in altitude of 1,200m/4,000ft.

We're "employing" mainly 4 nitrogen fixing trees (one of them is on constant debate - if it's really fixing nitrogen).

I would love to learn from you what nitrogen fixing trees work in your mediterranean garden or food forest.

We use the nitrogen fixing trees by:

Planting them in our food forest to feed nearby fruit or nut trees.

Pruning these trees regularly and use the cuttings as mulch around fruit trees and perennials to feed the soil from above.

Composting the cuttings to create a rich soil amendment for vegetable gardens.

If you have other ways to use them - I'd love to hear from you...

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 the…



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.

Fodder
Currently, the main use of tagasaste (mainly in Australia and New Zealand) 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 trees (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 masses of white flowers.

I would love to learn from you what nitrogen fixing trees work in your mediterranean garden or food forest.

Thank you.

Great post, Tagasaste will be on my look out for list. Here we are a lot wetter, but where you have water from grid runoff alder is a good nitrogen fixator, and California willow has recently been found to do so as well. Ceanothus/California lilac also fixes N and is up and down the state in much drier areas than where I am. I’d also consider nutrient accumulating trees like mulberry, which does so by attracting so many birds, which provide manure every time they land, take off, and eat.

Thanks a million, Ben...
Gonna check what I can get here in the Canary Islands from your list.

And I loved the idea of having nutrient accumulating trees.
I did plant 3 mulberry trees, but I guess those would take a few years to do the job with the birds...

Any other trees that would do the same type of job?
Make it a great day.

I think that in climates that experience more frost, tagasaste will be a disappointment.  I had a few and they all gradually died out.  I'm technically in a Mediterranean climate in inland California but I regularly get winter lows to 20F (-7C).  My main N-fixing trees that are thriving are black locust(Robinia), "mimosa" as Americans call it (Alibizia julibrissin), blackwood acacia (A. melanoxylon) and Casuarina cunninghamiana. Of these I would have to say the Albizia is the only one vigorous enough so far to be cutting any for forage or to consider coppicing, which is surprising since it is not native to a Mediterranean climate.  All of them are under drip irrigation though, so if I shut this off perhaps one of the others would edge into place of preference.

Thank you so much, Alder, for your information.
Although we are at altitude of 4,000ft/1,200m - we never get frost - and the Tagasate is thriving naturally all over the mountain.

I was looking for Albizia julibrissin to add to our nitrogen fixing trees for a couple of years, but couldn’t get my hand on them.
Would you be willing to send me some seeds, when you can collect them (as well as any of the other nitrogen fixing trees on your property)?
I’d be happy to pay for the shipment.

Make it a great day.

An update...

I found a seed store on our tiny island (an hour drive from us) that sells seeds of local and endemic plants and trees.

In their catalog I found several nitrogen fixing trees that I either didn't know existed, or didn't know they grow natively here...

Here are the seeds I'm thinking of ordering:

Cytisus scoparius (Broom)

Gleditsia sinensis (Chinese Honeylocust)

Caragana arborescens (Pea Shrub)

Hardenbergia comptoniana (Violet Sarsapilla)

Honeylocust

Myrica faya

Psoralea tenuiflora

Robinia hispida

Shepherdia argentea

Lespedeza bicolor (Shrubby Bushclover)

Adenocarpus foliosus

Genista

Teline

Cercis siliquastrum (Judas tree)

Anyone has experience (good or bad) with any of these nitrogen-fixing trees?
Thank you.

As for the broom, you are very likely better off with the Spanish broom, not the Scottish one. The hills in the South of France are often covered with its flowers (therefore called jeune in French). Judas tree also grows wild here quite a bit. Robinia is the most prolific here though, and I think has many other uses as well (poles etc, very hard wood).