N fix 3: Caragana arborescens


Being so easily grown, supremely hardy, stacking functions by making fruit, attractive flowers, biomass, nitrogen, and growing 10 to 15 feet Caragana  fits well into most designs. Unfortunately it doesn’t always.

My Peashrubs (the common name for Caragana) never grew well. Although in early spring they would burst with the most thick budding and greening, it was only to grow slower and yellow faster as the season progressed. They have eventually weaseled away to nothing.

One of these was a gift from a friend, all the others were the precious few I got from seed. With two successful sprouts out of 100 seeds, I would call that a fail (especially in comparison to Amorpha). Only one made it to my food forest, the other my Mother got as a gift for my graduation (I was home schooled and she was my teacher, so how could I say no?). For all the fertilizer and re-potting she gave it, it has remained green and growing to the extent of its pot. She finally planted it in the ground last year, and we’ll have to see what it does without pampering.

Failing to get good results myself, I purchased some year-old Siberian Peashrubs from Burnt Ridge Nursery that had nodules on their roots when they came, and so far these have grown fine. I found no nodules when moving my pathetic specimens trying to make them happy. Obviously my area is low on the right bacteria for Caragana to fix nitrogen, and I should have inoculated them either as seed, or as plants.

So this year I will have to try inoculating what’s left of my specimens, if any still linger, with just a simple combination inoculant. The main bacteria to infect Caragana are supposedly mesorhizobium species, as several Chinese studies found, so an inoculant that has these species should work. 


Another factor that could affect the growth of Caragana here, is that it seems to like a harsh climate. I came to this conclusion after starting my own from seed and wondering how in nature a plant could get the equivalent of a 180 degree water bath as I was directed to give them. I found that it often grows in deserts where the soil is so much sand, that the sand may blow away leaving the roots exposed to a depth of 4 ft. Talk about drainage! One must consider the seed would land on hot sand for some small stretch of time. So they may get the equivalent of a hot water bath after all.

Take a look at the map from the USDA plant database of where Caragana has naturalized and you’ll notice the majority of it is rather harsh climate such as Montana or the open fields of Ontario. So don’t shy away from planting your peashrubs in an unfriendly situation. They may love you more for it.

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Of course there are no worries about hardiness. It’s hardy to zone 2. Even its ability to fix nitrogen (about the same amounts as Amorpha, medium) is cold tolerant, staying active as low as 40 F.


Besides fixing nitrogen for the plants around it, it does manufacture some allelopaths. The only clear indications of what it affects is a single grass, Agropyron repens or couchgrass. There are suggestions that it effects many other kinds of grass. But I haven’t heard of anything concrete besides Agropyron. I would personally consider allelopathy to grass a plus unless you’re lining wheat fields and pastures with it.

On the flip side, Caragana has been noted in a lab test not to sprout when soaked in the allelopath juglone, which I’ve written about here. One review of this test noted that the juglone they used was in far higher concentrations than what could ever be found in nature. So the results were possibly exaggerated. Given its apparently sensitive chemical nature when its bacteria aren’t happy, I’d avoid guilding the two.


In guilds, Caragana has the excellent ability to grow just to small tree height of fifteen feet. Although when you want nitrogen, coppicing is best. If you don’t, you should be able to let it grow up to the canopy and not worry about shading too much. Thankfully Caragana’s pea-like fruits are hard and so can take falling from heights like this. Perhaps try laying a sheet under the tree and shaking to catch them.

Many people have suggested simply planting where chickens can get under it, and harvest the fruit for you which is a great idea in terms of efficiency. Consider how much the animals would be getting and perhaps read about the Canavanine content of the seeds before trying this. From what I have read, the seeds need to be thoroughly soaked before consumption to remove the Canavanine, among other things.


When giving my seeds their hot water bath, they slowly released a red-brown color into the water and a sweet smell not far off from lentils. Perhaps I can post a more thorough review of the seeds flavor in the near future now that my plants will be on track to do what they are supposed to.


  1. In my central New Mexico garden, few plants have required as much pampering as the supposedly indestructible C. arborescans, and even so, my one surviving plant has only grown five feet high in five years. I had planned to use the seeds as a supplementary food source for my chickens, but have given up on that idea. I started with potted plants grown outdoors, healthy and flourishing to the eye, but they were grown in the cold-desert country further north, and I wonder if our summers are too hot for them, or our winters not cold enough.
    My black locust, on the other hand, has grown about five feet a year.
    Thanks for posting about this and other fascinating topics.


    1. Five feet of growth in five years is better than the best of mine. I haven’t seen many references to Caragana having fast growth per say, so that might be alright for it. I’m curious if you’ve gotten much fruit yet? One of my three year old plants have put out a flower and now a fruit, so if you haven’t gotten any fruit yet, you should be verging on it.
      As for heat, Caragana likes extremes, but it prefers cold extremes more than heat extremes, when it comes to enduring long periods of them. Its bacteria prefer cooler temperatures, so putting it where it can get its roots deep to keep them cool would seem to be important.
      Thanks for the comment. I’ve read a lot of government reviews and studies on this plant but they all consider it to be an obnoxious weed whereas us gardeners can’t get the thing to grow, so I appreciate the info.


      1. You have been a lot more organized about this than I have. As soon as I read “nitrogen-fixing” and “indestructible” I said “That’s for me!” and ordered some without further research. I somehow got the idea that they grew rapidly, and it sounds like that’s not the case at all. I had a few blooms this year, for the first time, but haven’t seen any pods yet.


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