Thoughts on nitrogen fixing trees for the desert

I'm trying to figure out what the best course of action for nitrogen fixing in my budding food forest.  I've tried clover, but that doesn't survive here without supplemental watering which I'm trying to avoid as much as possible.  I've recently been looking into nitrogen fixing trees/bushes.  I know a lot of folks recommend using local nitrogen fixers, however the only local tree here is Mesquite, which doesn't play well with other plants.  I'd considered Black Locust and/or Russian Olive, but I see that a lot of people have had bad experiences with them being invasive/spreading.

Currently I'm thinking of Acacia trees, specifically Acacia seyal (excellent nitrogen fixer) and Acacia senegal which can produce gum arabic.  Seyal also produces something similar to gum arabic which can be used for inks, paints, etc.  Both can also produce fodder for livestock and to some extent people.  However, they might not survive the occasional sub-freezing temps here.

Any thoughts, or suggested alternatives?

FWIW Where I live we get about 16 inches of rain per year, with most of that falling between July and September. Temperatures here are mild (for Arizona), rarely getting over 100 degrees F and rarely falling below 20F during the winter.  Average highs during the summer are around 90F, and during the winter the average lows are just above freezing, typically warming up into the 50s during the day.

Howdy Peter! A quick USDA PLANTS database search for trees in the family Fabaceae that grow in Arizona returned this list:
                   
Albizia julibrissin
Caesalpinia gilliesii
Caesalpinia mexicana
Caesalpinia pulcherrima
Ceratonia siliqua
Cercis orbiculata
Erythrina flabelliformis
Eysenhardtia orthocarpa
Gleditsia triacanthos
Leucaena leucocephala
Leucaena leucocephala ssp. glabrata
Lysiloma watsonii
Mimosa aculeaticarpa
Mimosa aculeaticarpa var. biuncifera
Olneya tesota
Paraserianthes lophantha
Parkinsonia aculeata
Parkinsonia florida
Parkinsonia microphylla
Prosopis farcta
Prosopis glandulosa
Prosopis glandulosa var. torreyana
Prosopis pubescens
Prosopis velutina
Psorothamnus spinosus
Robinia neomexicana
Robinia neomexicana var. neomexicana
Robinia neomexicana var. rusbyi
Robinia pseudoacacia
Senna hirsuta
Senna pendula
Senna pendula var. glabrata

Not sure about everything on the list, but the Leucaenas, Mimosas, Mesquites and Locusts should all definitely fix nitrogen, particularly if they're inoculated.

Here's a paper on trees for New Mexico that might be helpful:
http://aces.nmsu.edu/pubs/_h/H426.pdf

Peter VanDerWal wrote:I'm trying to figure out what the best course of action for nitrogen fixing in my budding food forest.  I've tried clover, but that doesn't survive here without supplemental watering which I'm trying to avoid as much as possible.  I've recently been looking into nitrogen fixing trees/bushes.  I know a lot of folks recommend using local nitrogen fixers, however the only local tree here is Mesquite, which doesn't play well with other plants.  I'd considered Black Locust and/or Russian Olive, but I see that a lot of people have had bad experiences with them being invasive/spreading.

Currently I'm thinking of Acacia trees, specifically Acacia seyal (excellent nitrogen fixer) and Acacia senegal which can produce gum arabic.  Seyal also produces something similar to gum arabic which can be used for inks, paints, etc.  Both can also produce fodder for livestock and to some extent people.  However, they might not survive the occasional sub-freezing temps here.

Any thoughts, or suggested alternatives?

FWIW Where I live we get about 16 inches of rain per year, with most of that falling between July and September. Temperatures here are mild (for Arizona), rarely getting over 100 degrees F and rarely falling below 20F during the winter.  Average highs during the summer are around 90F, and during the winter the average lows are just above freezing, typically warming up into the 50s during the day.

I live in USDA Zone 4B so acacia (specifically Australian black wattle is what I wanted) is not an option for me. I settled on black locust as the nursery tree in my "natural orchard." The do spread by basal shoots (root suckers), so you do have to watch out for that and keep them mowed. The seed pods might need to be raked up each year, too, unless you want just mow seedlings every spring. Also all parts of black locust are toxic to chickens, so I'll be eliminating suckers and seed pods prior to anytime I let my chickens run around in there.

Black locust do NOT like shade and I'm surrounded by forest. So in planting them in the middle of my cleared land I can mange the root suckers/seedlings in that cleared area. If they spread into the forest, they'll never get established there. The upsides of black locust (N-fixing, very fast growing, likes full sun, drought tolerant, casts only light shade, great lumber, great firewood) far outweigh the drawbacks - but that's just my opinion. I am planning on harvesting the trees for lumber and firewood, BTW. Oh yes! Ask your extension office about the locust borer. Where I'm at woodpeckers are the only predator for the borer, so my trees will be vulnerable to that. One more thing to look out for...  

I also settled on silverberry and Siberia peashrub as N-fixing shrubs in the orchard. Delicious, nutritious food, super fast growing, etc. They are good in sun and shade... they do well in heat, in cold and in drought. Ask me in 3-5 years how well they worked out

Good luck and have fun!  

i have northern buffalo berry and goumi and seaberry. all are drought tolerant nitrogen fixers. the buffalo berry is native to the west and has a variety that grows down your way. i was down to Yuma last week and there isn't much growing away from the colorado.

I have Caesalpinia Gilliesii, Autumn Olive, and just ordered Lead Plant seeds. Lead Plant looks like a fascinating option for me in 8A.

I can't be sure about Russian olive, but my autumn Olive haven't spread at all. I wish they would.  The only plant I have that spreads to the point it could be a problem is seaberry.

I forgot about my thornless Honey Locusts. I’m confused about their status as far as N. Fixers, but what the heck.

Todd Parr wrote:I can't be sure about Russian olive, but my autumn Olive haven't spread at all. I wish they would.  The only plant I have that spreads to the point it could be a problem is seaberry.

seaberry is shade intolerant so not a issue with invasiveness. its been studied thoroghly.

This is a very interesting PDF talking about nitrogen fixers, by the Sustainable Ag Research and Education organization.  

It contains a really nice chart that shows secondary uses of nitrogen fixers.  Includes organic matter, fodder, food, timber, live fence, fuel wood, shade, ornament, windbreak, salt tolerant, dry/drought tolerant, poor drainage, acid, alkaline, and height.

Nitrogen Fixers Guide including use chart

Peter, I'm originally from that area and in my experience mesquites are a good thing to have around. However, my situation was urban (central Tucson) and what I had growing in close proximity to my three big velvet mesquites were mostly cacti, fruit trees including citrus and figs, and various food plants in containers like chiles, eggplants, tomatoes, lemon grass and some other herbs. Oh, and chickens (one tree was the shade giver for the poultry run). What I found was that container plants that got heat or water stressed in full sun in the summer would do much better under the dappled shade of the mesquites. The leaf litter would get blown or washed into the low spots in my yard, which were the tree basins for the citrus and other fruit trees. This gave them a nitrogen boost. The beans would drop in the first part of the monsoon season and I'd toss them in the chicken pen as free high-quality feed.

I'm guessing you're up a bit higher and farther from the city, so you probably can't grow Prosopis velutina successfully...P. juliflora is likely to be your only hardy species and I don't think it gets as big, but should fill a niche if you're willing to manage it a bit with pruning. Don't get one of the Chilean or Argentine varieties, as those really did seem to show lots of allelopathy and cast too much shade to allow a healthy understory.  Silk tree (Albizzia) might work for you, and honey locust is tough enough to make it in places like Patagonia and Bisbee with maybe some water in May-June while it's getting established. Redbud is native to the lower elevations of the Grand Canyon and I had a small one growing as an ornamental.

What about Siberian peashrub? How well does that handle semidesert conditions? I see a couple others have mentioned seaberry, and that is tough as an old boot. You could also look into lupines, vetches (locoweed is a great one) and sennas. The native catclaws are pretty awesome and all over the middle elevations of the borderlands, but those thorns would be a deal breaker in close quarters. That could be an issue with locust as well.

I lived in Phoenix and this is what worked for me.   Acacias are a  no-brainer. I have read that they aren't great nitrogen fixers but they are fantastic shade trees, create biomass and are a great way to create shade zones for the more tender nitrogen fixers.  

Mesquite is supposed to be a good nitrogen fixer and they do well in the climate.

Another, slow growing, tree you could use is Olive.

I planted six Spanish Arbequena olive trees in direct sunlight, watered them in the first year and then did nothing.  They grew well and produced fruit, they are semi evergreen and just a beautiful tree.    I also planted some Italian varieties of Olive but I don't remember the names.  I imagine that some of the olives grown in the southern parts of Italy, Sicily and Greece would do well.  Bird of paradise,

steve bossie wrote:

Todd Parr wrote:I can't be sure about Russian olive, but my autumn Olive haven't spread at all. I wish they would.  The only plant I have that spreads to the point it could be a problem is seaberry.

seaberry is shade intolerant so not a issue with invasiveness. its been studied thoroghly.

When you have some extra time, please explain that to my seaberry plants. It seems they haven't read the studies.

From what I understand, you're in Arizona, yes? There's actually a huge number of local nitrogen fixing plants that could be of use, hopefully. While some of the trees, like mesquite, ironwood, and palo verde, fix nitrogen, as you noted, they sometimes don't play well with others.

However, there are some great perennial small bushes and even some annuals that are quite nice.
from the Fabaceae family (legume family)
1. the Caesalpinia sub-family - while palo verde is here, so is the Mexican Bird of Paradise (Caesalpinia pulcherrima), and the little cassias (cassia covesii).  The latter is listed as a mild medicinal in herbal literature.
2. the Mimosa sub family - this one has the mesquite and acacia, but it also has fairy dusters, which are pretty little bushes with pink fluffy flowers that'll fix a little nitrogen for you.
3. the Papilionoideae (pea) sub family - while this is the subfamily ironwood is under, there are also quite a variety of native lupines that are here, as well (seeds are for sale in many desert nurseries)  They tend to reseed fairly easily, and have lovely purple/blue flowers. Dalea make small bushes with lovely purple flowers. There are also some local clovers here that might do well, if you can collect some seed or find a local nursery that sells them. There is Desert Rockpea, and a couple Deervetch as well, although I haven't found the latter two for sale anywhere (this link lists some of them - http://www.arizonensis.org/sonoran/fieldguide/plantae/papilionoideae_p2.html )

@Shauna - the Dalea tip is a great one...I had almost forgotten about those. Much nicer than Mimosa. (Whoever named it fairy duster had a twisted mind. Ankle slasher, sock shredder, pant ripper, bloodthirsty demon hell spawn are a few names that come to mind. Since it grows in association with shindagger I have a hard time deciding which one is worse. Probably shindagger, since those tips can break off under your skin.) :-(

Lysiloma is another really nice leguminous subtree from that region, but I think it's less frost hardy and might be difficult to establish. It is listed on a couple of plant sites as being tolerant down to 20F, but that may only be mature trees.

Sophora is great genus of legumes and the mescal bean (S. secundiflora) is hardy down to 0F. They grow reasonably fast and have a nice compact form.

I'd be interested to hear what you did go with and how it has worked out. I'm starting this process in a similar climate.

Phil Stevens wrote: Much nicer than Mimosa. (Whoever named it fairy duster had a twisted mind. Ankle slasher, sock shredder, pant ripper, bloodthirsty demon hell spawn are a few names that come to mind. Since it grows in association with shindagger I have a hard time deciding which one is worse. Probably shindagger, since those tips can break off under your skin.) :-(

lolz

I'm curious why a couple of you have said that mesquite doesn't play well with others. Mesquite are known locally in Spanish as madrina because they help to nurse so many other species along here in the Arizona desert. We plant all our new bushes and trees around mesquite (ours are mostly Prosopis velutina), and we collect leaf litter from under lots of mesquite around the property to use as mulch to help nitrogen-hungry plants that we can't huddle under mesquites. Since mesquite deadwood is our primary fuel for heating and cooking and busting it up produces lots of woodchips, that's our primary woody mulch material, too. We haven't noticed any kind of adverse effects on any other plants from all this; quite the opposite. Of course mesquites have thorns, and of course we get cut and pierced by them all the time (mostly collecting firewood, but also doing things like planting under them), but it seems a pretty small price to pay for the abundance that mesquite represent in what can be a very challenging climate.

Can't speak for others, but one issue I've had is competition for resources.

I have found mesquite to be a fantastic tree in the areas on my property where I want native plants - they have provided enough shade to help protect against the worst summer sun, but not too much. The leaf litter has been great mulch in my experience, as well.  I have a lot of native plants grow up under our mesquites. Pods are great eating. Mesquite sap and leaves are mild medicinals - overall, I love 'em.

however, the mesquites nearest some of my non-native plants that require frequent irrigation seem to send out roots that way and I find I end up having to water more and more frequently to keep the plants from drying out. So having mesquites near my fruit trees has been problematic. Also, some folks may be thinking of non-native mesquite, the ones from south america. THOSE suckers are nightmares. Very heavy shade that makes it hard for anything to grow under them. Pods are bland and blech.

Hi. Have you seen what via Organica in Mexico are doing with a mix of Nitrogen Fixers and Agave, to create fodder for sheep while reversing desertification and Sequestering Carbon:
https://ecosystemrestorationcamps.org/agave-power-how-a-revolutionary-agroforestry-and-grazing-system-in-mexico-can-help-reverse-global-warming/

Thanks so much for the link, David! That sounds potentially like a really great system, although I can't help but wonder if anyone has looked into how much, if any, methane is generated during the fermentation of the agave and legume silage into digestible animal feed, and whether or not that offsets the carbon sequestration in terms of climate change effect. Livestock can and do eat mesquite and other leguminous trees' foliage, as well as things like yucca stalks that tend to grow in the same areas (cows do, anyway), as it is without fermentation. I wonder if the focus on carbon sequestration is over-complicating the system while the fermentation of the agave leaves may be canceling out the potential benefits of the sequestration. I wanted to comment and ask those questions of our old friend Ronnie Cummins, who wrote the article, but there doesn't appear to be a comments section. Does anyone here know if anyone has looked into these things further?

Like Via Organica and like the majority of farmers and ranchers in Mexico that Cummins mentions, we don't have groundwater irrigation here, and we don't have much collected rainwater to spare for irrigation after we make sure we have enough to drink and cook and clean ourselves with (although certainly we use every drop of that greywater), so we rely primarily on whatever precipitation falls directly and we can get to stick around as long as possible in the soil, etc. That means we only attempt to grow trees and other plants that can survive this kind of tough love. Mesquite and acacia are especially important in this kind of system. In addition to their nitrogen-fixing capacity and nice leaf litter and wood chip mulch, mesquite provide some of the only shade around here, and in the brutal early summer and even parts of the monsoon season (if we ever get a monsoon again), that shade can be all that keeps other plants alive. At our other property that we're just beginning to observe and plan out, there are more whitethorn acacia than mesquite or catclaw acacia, and those also produce very nice shade (and deadwood like rocket fuel! man, those dry limbs in a woodstove burn hot and just keep burning).

Beth Wilder wrote:I'm curious why a couple of you have said that mesquite doesn't play well with others.

I think it gets a undue bad rap here in AZ and other areas.

One of the ideas is that mesquite had invaded/overtaken native grasslands (which is true), mostly due to cattle overgrazing ....
....and NOW somehow if they eliminate the mesquite via poisoning and/or physically removing it .... the grassland will some how return.
...the idea that the grass and mesquite are competing.

I think that's fools errand, with out instituting some real radical changes with the cattle management.

Sure there's some competition between the two (mesquite & grasses), sure,  
but the elephant in the room is how bad the land is degraded;
and the overgrazing and bad cattle management;
and that one could ever get back to what was before.

Beth, are you able to collect enough rain water for your needs without the monsoons?  I'm considering moving to Arizona (looking at several possible places, Arizona is just one of them, partly because one of my brothers lives there), but am dubious about the water situation.  I really, really don't want to have to truck our water in.

What part of Arizona?   Rainfall totals vary wildly through out the State.

Could be 5" to 30" annually.

Kathleen, Mikhail is definitely right, and also historical averages in each area are increasingly inaccurate.

Where we are, the average had been 13" precipitation (inc. a bit of snow)/yr. Last year we got much less than that. We still have enough water for our meager domestic needs for now, mostly collected in 2019 and the winter of 2019-2020, which was actually wetter than usual. But if we don't get a monsoon again this summer, we will run out within a year, I'm pretty sure. We had essentially no precipitation over this last winter. They're saying that this year will be even drier across the West than previous years of the drought, and possibly the driest in millennia, but we've also heard that the monsoon might start earlier than usual and might be wetter (although "than what" -- than last year? not hard. than usual? better, but seems unlikely -- wasn't made clear).

I would definitely be dubious about the water situation if I were you. I'd say we're more irate and galvanized than dubious and are doing all we can to fix what we can (using political means). Normally I'd say it might be a good idea to drill a well as a back-up to raincatch, but all our wells have been running dry, so what's the point? If we keep not getting monsoons (and winter precipitation) and factory farms and other heavy corporate users keep draining the groundwater at rates much, much faster than possible recharge, we will continue to have increasing and worsening problems, including that residence in these areas will be increasingly impossible.

Thanks.  I was thinking about the areas where you can grow a lot of tropical stuff.  My brother and his wife winter in Quartzsite, going to Idaho or home to Alaska for the summers (they live in their motor home and the AC can't keep up with Arizona's summer heat).  I think that area is too dry for what I want to do.  I may have to stick to the more humid climates.  We've been in Kentucky for three years, love it in some ways, but my oldest daughter has moved to Texas (she and the grandkids were the main reason we moved here from eastern Oregon).  I want to move farther south, where we can grow things like bananas and citrus, but I'm not extremely fond of high humidity.  On the other hand, water is a necessity of life!

Parkinsonia(Jerusalem Thorn).  Geoff Lawton talks about Greening the Desert project in Jordan. He has a lot of videos on YouTube talking about a nitrogen fixer with thorns and a lot more ways to create soil and clean water to use as watering system.  https://youtu.be/yI9wMtTvWps?si=iQwbtSHjTnKC38JE

Parkinsonia aculeata (Jerusalem Thorn). Leucaena leucocephala (White Leadtree) is the tree without the thorns.  Geoff Lawton talks about Greening the Desert project in Jordan.  He has a lot of videos on YouTube talking about a nitrogen fixer with thorns and a lot more ways to create soil and clean water to use in gardens.  Ways to build in Jordan that they used for living in and using.  Tons of information.  Desert fixing isn't easy, but it will take time.

One tree you can grow in AZ that no one mentioned here that fixes nitrogen is the Tipuana Tipu tree.  It is beautiful, has awesome flowers and grows extremely fast.  Great shade tree!

Hi, Greg.

Welcome to Permies!
Great first post, by the way.