Nitrogen Fixing Trees

I’ve mentioned nitrogen fixing plants and the bacteria that goes along with them before in posts like this one.

Until now I have always thought of these in terms of vegetable crops, but recently I came across a mention of nitrogen fixing trees, especially for use together with fruit trees or for revitalizing soil. Trees have an advantage over smaller plants because their deep roots can fix nitrogen far below the surface.

The first thing I found is most nitrogen fixing trees are only suited to the tropics, and I live in a northern temperate climate.

One of the trees I found suited to my climate is the Black Locust (a type of Acacia tree).  However, it’s fast growing and reaches a height of 15 meters, which is much too large for my tiny community garden plot.

Another more likely candidate is the Green Alder, but possibly reaching over 8 meters it’s still a bit on the large side. Since this is a more of a bushy plant, I suppose it will be easy to cut it back if it gets too large.

Does anyone have any suggestions for a small nitrogen fixing tree or bush for northern climates? Does anyone have any experiences with this kind of plant?

11 Replies to “Nitrogen Fixing Trees”

  1. My first thought was grey alder – is there a green alder? I understand that grey alder is used on slag heaps to stabailize and fertalize the soil. Then of course common alder does the job too, and it’s easy peasy to grow from seed. Alders have an interesting folklore too, especially if you’re into Wagner.

    Second thought is sea buckthorn – Hippophae rhamnoides – there’s a good display of them at Westonbirt arboretum – http://www.forestry.gov.uk/westonbirt – well worth a visit in any event. I’m not sure about it being nitrogen fixing but it’s a good pioneer plant on loose soils.

    Simon

  2. Hi Patrick,

    Happy New year!

    Just wanted to tell you that we’re now gearing up for round 2 of the Garden Bloggers’ Carnival -a bit different this time, in that I’m asking people to nominate a post from another person’s blog. Full details on my blog today (Jan 3rd). I hope you’ll participate again, like you did last time. And of course, if anyone else reads this, please join in!

    Sue

  3. Hi Patrick
    I think that lupin and lupin trees are worth considering. I have used lupin as a green manure in the past.

  4. Wow, thanks everyone! To be honest I don’t know a lot about plants that aren’t common fruits and veggies, so all these suggestions are really eye openers for me. I’ve never had fruit from the Gumi or nuts from the lupin, and even if they don’t turn out to be the most exciting foods they might be really nice to have in the garden as nitrogen fixing plants. The different alders people have suggested are handy because they are native plants I should be able to find locally.

    Someone else in a private email suggested Laburnum and Caragana.

    To be honest, I’d like to try all of these, and will keep an eye out for sources of seeds and plants.

    Does anyone have any seeds they could send me?

  5. I would advise you not to try and eat either the lupin or the laburnum tree. They are both poisonous.

  6. Hi Tony,

    I think you’re right for most varieties of lupin. What made me think of eating them was this Wikipedia article on how one variety is eaten as a beer snack in southern Europe:

    http://en.wikipedia.org/wiki/Lupin_beans

    For the laburnum there’s no doubt. It’s something to keep in mind before I even plant it.

    Thanks for pointing this out.

  7. Het eerste waar ik aan dacht was inderdaad de grauwe en de zwarte els.

    De honingboom komt van de vlinderbloemenfamilie en fixeert ook stikstof. Hoewel deze uitheems is, kan deze in Nederland groeien.

    Maar dit zijn uiteraard grote bomen.

    Wat Simon voorstelde past beter bij je denk ik. De Duindoorn, alleen deze plant heeft een zanderige ondergrond nodig.

    “De duindoorn (Hippophae rhamnoides) is een tweehuizige struik; er zijn mannelijke en vrouwelijke planten. De plant komt van nature vooral voor in open, kalkrijke duinen.”

    Verder kan ik me geen boom bedenken.

  8. Je kan natuurlijk ook een boom laten groeien en nadat die 1 a 2 meter is geworden hem omhakken.

    Dan komt allemaal stikstof vrij en je kan je hout gebruiken.

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