Nitrogen fixing trees in the Southern USA food forest

Good day, Stefan! It is very nice of you to answer questions and I see there are quite a few very excellent questions already been tossed out at you. I have a very newbie permie question for you.

I am looking at options for planting nitrogen-fixing trees and nutrient accelerators amongst my fledgling food forest and would welcome ideas of good trees to consider or to avoid.

I'm in zone 8a (or is that 7?) on the southeast coast of NC. My homestead is a mere .6 acre.

Currently planted: Santa Rosa Plums (3 of them) and a blueberry (lone survivor of a planting of 9), and 9 mulberries. I also have 60 bush willows (SX61) planted as a fodder source for rabbits. (There are also 4 mature pecan trees, a number of young pecans planted by squirrels, and a couple of oaks and a holly tree which I hate.)
Planned for planting (or trying again): figs, blueberries, peaches, apples, Chojuro Asian pear, strawberries, Chickasaw plums, muscadines

One tree that I've read to be a good nitrogen-fixing tree in our area (if somewhat invasive) is the Mimosa (Japanese silktree) (Albizia julibrissin). I've also got a lead on some Autumn Olive seedlings. Other than that, I'm open to ideas.

Hey Tina I am in a similar zone to you, with similar plant selections. In my garden I have gone ahead and planted 4 Mimosa trees. I got the seedlings from a friend who has a fully mature Mimosa, and they have had no issues with it suckering. It is a heavy seeder so I expect to have to pull out sprouting seeds eventually (like I already do with redbuds, hackberry, pecan and oak) But I grew up with a Mimosa tree so it is one of those familiar plants I like.

I am allowing quite a few pecan tree seedlings to grow up in the garden, their taproot does good things in puncturing down and getting nutrients. Other trees I have planted for dynamic accumulation and chop and drop are mulberry, hackberry, and redbud. All these trees were easy to get for free and they grow so readily.

I would never plant ailanthus altissma in my garden, but I have a large one nearby that I chop and drop all the suckers off in the chicken forest. This would be a great fast growing accumulator if it was not such a colonizer.

Looking forward to what Stefan has to say on this.

Tina Paxton wrote:One tree that I've read to be a good nitrogen-fixing tree in our area (if somewhat invasive) is the Mimosa (Japanese silktree) (Albizia julibrissin). I've also got a lead on some Autumn Olive seedlings. Other than that, I'm open to ideas.

I have heard yes and no on if Albizia julibrissin really fixes nitrogen or not. This seems to be similar to the honey locust where it doesn't have nodules like most nitrogen fixing legumes, but there are lots of people that say it does anyway. Personally I am looking at planting both mimosa and honey locust for the fodder value alone and if they happen to fix nitrogen, all the better. I have a few mimosa already and will be collecting seeds from them this fall and buying several pounds more. I plan to plant the seeds in dense rows in a pasture to use as a fodder crop following Jaime Elizondo's approach.

Paul Ewing wrote:
I have heard yes and no on if Albizia julibrissin really fixes nitrogen or not. This seems to be similar to the honey locust where it doesn't have nodules like most nitrogen fixing legumes, but there are lots of people that say it does anyway. Personally I am looking at planting both mimosa and honey locust for the fodder value alone and if they happen to fix nitrogen, all the better. I have a few mimosa already and will be collecting seeds from them this fall and buying several pounds more. I plan to plant the seeds in dense rows in a pasture to use as a fodder crop following Jaime Elizondo's approach.

I get a lot of mixed-messages about Albizia julibrissin both as a nitrogen-fixer and as a fodder food. But, I love them so I grab for every positive word I can find for them! Wouldn't you know it...my first attempts at growing some for myself have failed. This year, I'm planting the seeds directly in the ground instead of trying to start them in pots.

I'll have to google Jaime...a new name for me...always something new to learn! -- not finding him in google...do you have a URL?

Zach Muller wrote:Hey Tina I am in a similar zone to you, with similar plant selections. In my garden I have gone ahead and planted 4 Mimosa trees. I got the seedlings from a friend who has a fully mature Mimosa, and they have had no issues with it suckering. It is a heavy seeder so I expect to have to pull out sprouting seeds eventually (like I already do with redbuds, hackberry, pecan and oak) But I grew up with a Mimosa tree so it is one of those familiar plants I like.

I am allowing quite a few pecan tree seedlings to grow up in the garden, their taproot does good things in puncturing down and getting nutrients. Other trees I have planted for dynamic accumulation and chop and drop are mulberry, hackberry, and redbud. All these trees were easy to get for free and they grow so readily.

I would never plant ailanthus altissma in my garden, but I have a large one nearby that I chop and drop all the suckers off in the chicken forest. This would be a great fast growing accumulator if it was not such a colonizer.

Looking forward to what Stefan has to say on this.

I never thought of pecan trees as dynamic accelerators...cool. I know some of these saplings will have to go eventually but for now they aren't in the way and they produce plenty of mulch material. ummm...chop and drop mulberries? Only if my rabbits don't eat it all!! hehe (mulberries are a good high protein fodder). Your mention of the redbud got me thinking of the dogwoods we have...I tried mostly unsuccessfully to grow more from seed...this horticulture thing definitely has a learning curve!

Sorry, Google "Jim Elizondo" which is what he goes by most often. He used to ranch in Northern Mexico until it got too dangerous there. He is now in Florida using similar techniques of high density fodder trees/shrubs in Bermuda and Bahia pastures. You can find more info at these places:

https://www.facebook.com/Regengraze

http://beefproducer.com/blogs-Jim-Elizondo-61-fcb

http://www.regengraze.com

http://www.cam.ac.uk/research/news/sustainable-livestock-production-is-possible

I've started mimosa (Albizia) from seed both where I used to live in GA and here in CA. Nick the seed and soak overnight, and they come up easily. By the time I transplant to larger pots or plant them out, there are usually plenty of nodules on the roots without bothering with deliberate inoculation. The nodules are active based on their being reddish when broken open. Other benefits....it casts a light shade that lots of other plants don't mind, especially in hot summers.....and if it gets too much, it coppices readily. Leafy prunings are goat candy....if you have goats.
It's hard to find, but Albizia kalkora is worth checking out. There's a huge one at the Raulston Arboretum in NC....probably 18 inches thick and a single trunk up to a high canopy.....impressive. I hear it's begun to spread around that area and hybridize with A. julibrissin.
Once you get to the vicinity of Gainesville FL, or perhaps further north along the coast, options increase as warmer-origin legumes begin to appear.

I read somewhere that A.Julibrissin fixes nitrogen at a rate comparable to alfalfa, but that it also may be highly allelopathic. Can anyone weigh in on the allelopathy from personal experience? Dave Jacke's book "Edible Forest Gardens" vol 2 has it on the watch list because it's dispersive and exotic, (but also says it's a nitrogen fixer and outstanding hummingbird plant). It doesn't mention allelopathy.

This one basically says that a water-solution of A.J. doesn't seem to inhibit germination:
http://www.warren-wilson.edu/~research/Undergrad_Res/NSS2010-2011/AbstractsSpring2011/CHollifieldAllelopathy.pdf

wikipedia claims it's allelopathic
https://en.wikipedia.org/wiki/Albizia_julibrissin#Invasive_species

I have a bag of seeds I got from RF Shumacher, but I haven't planted them yet because of uncertainty about the allelopathy issue...

We have several mature A.Julibrissin here some with 40'+ diameter crowns and the grass grows very well under them. I can't say if this is because of nitrogen fixing or just that the foliage is not very dense and a lot of light gets through, but there is enough to moderate the climate as well to enhance growth. There are some on the fencerows by the road that have wild plums, hackberries, grass, and misc weeds growing under them fine.

Paul Ewing wrote:We have several mature A.Julibrissin here some with 40'+ diameter crowns and the grass grows very well under them. I can't say if this is because of nitrogen fixing or just that the foliage is not very dense and a lot of light gets through, but there is enough to moderate the climate as well to enhance growth. There are some on the fencerows by the road that have wild plums, hackberries, grass, and misc weeds growing under them fine.

Very good. I've noticed the same here -- mimosas being in mixed plantings rather than by themselves. Which, I suppose, dis spells the notion of them being allelopathic.

Excellent news, thanks for the replies. I wish I could dig up the original source that listed it as allelopathic, but I've lost the link. I thought it was the USDA Plants site, but looking through there now there's nothing about allelopathy so I must have mis-remembered.

Apparently, too, the blooms of A. julibrissin are becoming popular as a calming medicinal tea, originally from Chinese medicine I think.

Erik Lee wrote:Excellent news, thanks for the replies. I wish I could dig up the original source that listed it as allelopathic, but I've lost the link. I thought it was the USDA Plants site, but looking through there now there's nothing about allelopathy so I must have mis-remembered.

If there is one thing I've learned while trying to determine what plants are truly safe to feed to my rabbits -- there is a plethora of misinformation out there! My motto now is -- research...then observe. Yes, that includes having a "test bunny" to test out questionable plants....haven't lost one yet because either the plant proves safe or the rabbit proves smart enough not to eat it. Anyway, that bit of rabbit trail (pun intended) was just to illustrate that the permie motto of observe observe observe will always trump "the experts".

Alder Burns wrote:Apparently, too, the blooms of A. julibrissin are becoming popular as a calming medicinal tea, originally from Chinese medicine I think.

Gotta love that! talk about a win-win-win!

Tina Paxton wrote:Good day, Stefan! It is very nice of you to answer questions and I see there are quite a few very excellent questions already been tossed out at you. I have a very newbie permie question for you.

I am looking at options for planting nitrogen-fixing trees and nutrient accelerators amongst my fledgling food forest and would welcome ideas of good trees to consider or to avoid.

I'm in zone 8a (or is that 7?) on the southeast coast of NC. My homestead is a mere .6 acre.

Currently planted: Santa Rosa Plums (3 of them) and a blueberry (lone survivor of a planting of 9), and 9 mulberries. I also have 60 bush willows (SX61) planted as a fodder source for rabbits. (There are also 4 mature pecan trees, a number of young pecans planted by squirrels, and a couple of oaks and a holly tree which I hate.)
Planned for planting (or trying again): figs, blueberries, peaches, apples, Chojuro Asian pear, strawberries, Chickasaw plums, muscadines

One tree that I've read to be a good nitrogen-fixing tree in our area (if somewhat invasive) is the Mimosa (Japanese silktree) (Albizia julibrissin). I've also got a lead on some Autumn Olive seedlings. Other than that, I'm open to ideas.

Tina you live in one of the nicest places on earth. I worked one fall at Mattamuskeet National Wildlife Refuge in East central NC. If I had stayed 3 more months I would have never left. Fantastic people, pace of living and environment.
You already have a great thread for answers. Sounds like your choices are good. I would like to hear from others what would be great N fixing shrubs, max 10'. Since many plants Tina is mentioning are shrubs or small trees. I'm not familiar with mature mimosa height. A few more N fixers would be nice, suggestions of others??

Lespedeza comes first to mind as a leguminous perennial/shrub.

I have started growing lablab purpueus this season. I am growing it on a short fence so it will be more like a shrub then a vine. By the end of the season i am hoping for something like this picture.

Tina: before determining what nitrogen fixing trees to plant you may wish to examine the natural pH of your soil. If you only have one surviving blueberry bush chances are high you do not have the acidity to grow blue berries where you are. pH effects what nutrients are available to which plants. if you have alkaline soil or a soil nearer to alkaline than acidic, then you either will need to acidify your soil (which is a long term proposition for a sustainable food forest) or work with what is there naturally.

Once you find out the pH of your soil in various areas, then you can simply google what plants grow best in South East NC then find out which have a similar pH (acidic or basic/alkaline) then cross reference the two. You can do this for veggies and perennials and long term trees also. If you ignore the pH and simply plant what is a nitrogen fixing tree but do not consider the chemistry of your soil, those trees or plants will die--simply put, plants who thrive in higher or lower pH often do poorly or die if they cannot get the nutrients that they need.

Some plants can thrive in either, but some are very pH specific--blueberries need a very acidic soil as do some other berries and plants. if your soil is sweeter, you can always use raised beds and try to create a more acidic soil for what you wish to grow.

if you simply try to change the pH of your natural soil you will have to keep doing this as the soil amendments you add will often leach out when water passes through as it will not be the dominant soil. So... find out the soil pH, then find out what grows in your area then match what has similar pH to your existing soil. You CAN effectively change your soil pH if you are willing to add a very large amount of humus and compost and chemicals that will change the pH.

Mimosa is a non-native invasive plant, the seeds are wind blown and spread fairly quickly.  I would not recommend using at all.  My neighbor up the hill has one or more mature, and just about any bare soil in my yard maybe 500 feet away is subject to the seed sprouts.  

Black locust used to be planted for its nitrogen fixing capability, but it’s thorny.  Some use clover.  There may be some other native legumes, like partridge pea that I don’t remember.  

If I was going with a non-native invasive, which I still suggest not to use, would be Sericea lespedeza.  Some of our pine stands on eroded piedmont soils, really responded to the nitrogen fixation, and it goes pretty dormant in a closed canopy, but re-emerges when harvesting and opening the area to sunlight.  Sericea is still commonly used along road construction or maintenance activities, so it’s probably not going away, but it’s persistent.  

I love the mimosa tree so when I asked dear hubby to plant one for me he talked to our nursery guy who said that the male, if I remember correctly, does not produce seeds.

The tree we planted never had seeds.

Native nitrogen fixing trees and shrubs in the Southeast:
Robinia pseudoacacia
Robinia hispida
Robinia viscosa
Gleditsia triacanthos
Gleditsia aquatica
Alnus serrulata
Gymnocladus dioicus

Non-native nitrogen fixing trees and shrubs for the Southeast:
Albizia julibrissin
Albizia kalkora
Albizia coreana
Gleditsia japonica
Gleditsia sinensis
Gymnocladus chinensis
Eleagnus pungens (highly invasive)
Eleagnus umbellata (highly invasive)