Growing Amorpha

Deep purple petal over bright orange stamens of Amorpha fruticosa melt into green, spotted little crescents of seed. These ripen in the sun to a dark brown, then white-gray and hold. I kept thinking these seeds would fall off, but even in January when I lately picked some, they were tightly attached.

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They have a peculiar ability to sprout without cold -unlike most woody perennials that need months of subfreezing temps. They just need heat above 70 degrees F, and up pop little green leaves. Usually I soak the seed for a couple hours before sowing into flats. I start them in February in some years, March in others, but for my climate these both mean heat has to be provided.


I have to be careful with the dry air of indoor heating to keep the seeds wet, so usually cover with some plastic, and water often. We begin heating a small portion of our greenhouse about that time for garden vegetables, so these seedlings can soak up real sunlight from day one.

They are wise little seeds, and spacing their sprouting time -which outdoors would be a fail-safe against late frost and other catastrophes. For me, it’s a great convenience. Out of one ‘source flat’ as I call it, sprouts pop within three days after planting, but keep popping up for several weeks.

Usually I wait until the first true leaves show before I begin transplanting, then clear the flat of any sprouts with true leaves once a week.

Out of the hundreds I have grown, I find it’s best to start the seeds with potting soil, or compost with good levels of nitrogen. From here I separate into small pots or cell flats no larger than 2 inches across, filled with the same kind of nitrogen rich potting soil they sprouted in.

The heat and rate of drying in smaller pots, where the roots can quickly reach the bottom and be air pruned, has given superior results for me. They still develop very deep taproots once in the ground, but this root pruning while in the pot is helpful -in part because it stimulates more branching of the root system. Planting in extra large pots with nitrogen rich soil, many seedlings rot, and must be replaced two or three times over before each pot successfully grows a plant. On the other hand I have tried planting them this early in nitrogen poor soil, and they make little headway.

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I think this best mimics the situation they would find in nature. Forests and grasslands have a thin layer of nutrient rich, fluffy soil on the surface usually, which quickly becomes clay or whatever the base soil of the area. I want to get the seedlings into nitrogen poor soil to induce nodulation (aka hosting nitrogen fixing bacteria as evidenced by the formation of little nodules). This is spurred on by a lack of nitrogen in the soil. The catch is it takes time for the young plants to find the bacteria and get the symbiosis set up.

Nature’s way seems to be nutrient rich soil at first, then less rich soil as the plant gets bigger, the roots deeper. My contrived biomimicry that gives best results is moving the seedlings once they have filled their small pots and gotten a bit root pruned (not pot bound, as in roots turning back on themselves) into larger pots of whatever size you choose, filled with nitrogen poor soil about 1/3 rd coarse sand. I usually mix nutrient-rich rock powders, such as carbonitite or granite, into this before filling the pots.

Usually I transplant into 4inch pots at this point so they are filled with their roots in a couple of weeks -about the time nodules start to form. Usually this is early June -plenty of time for establishment before fall. Those I don’t get in the ground the first year go into gallon pots by August, which they usually have amply filled by next spring.

I try to avoid keeping Amorpha in pots more than a year. They grow best put in the ground as soon as possible after they have acclimated to the nitrogen poor soil. After years of refining this method, I’ve had transplants pushing 5ft by the end of year one -well on their way to exploding every spring with growth, providing some of the best organic matter for fueling your plant projects.

Where to get the seeds? You might have a plant nearby, which I recommend you snatch some seeds from. Otherwise they’re very affordable, and widely available from Sheffield seeds (my first choice), Oikos Tree Crops (They advertise A. californica, but I’ve gotten their seed -and plants, and compared it against pictures and attributes on the USDA plant database, and they have the name wrong. It’s species fruticosa), or even Amazon if you shop there.

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13 thoughts on “Growing Amorpha”

  1. The seeds I received of Amorpha californica twenty years ago that I made my planting came from an arboretum. It is possible they sent me the wrong seeds. It could happen. But the images of the foliage and flowers here look a lot different than fruiticosa. Additionally some of the plants are now 12-15 ft. tall. There are some similarities and possibly there might be even hybrids considering where I got them but for now they will remain Amorpha californica unless there is more compelling evidence.

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    1. Thank you, Ken, for commenting. I hope you understand I wasn’t trying to defame you or your company in any way. I have actually tried a couple of times to contact you on this point, but your contact system was glitchy at the times I tried. I so appreciate you being open about this.

      Have you looked at the USDA database? The seeds they have pictured for californica are reddish brown and smooth, the seeds of fruticosa lighter brown and mottled.

      The plants pictured were grown from your seed. Out of all the plants I have grown, I have noticed significant variations in stem color and number of leaves, so perhaps it is just hybrids we’re talking about.

      I underestand fruticosa is the species most likely to attain such tall heights, and that californica rarely gets as tall. If you find more information to clarify, I would love to know, and will gladly edit the post if you do. I have been subscribed to your blog for years now, and will keep an eye out for any updates on the findings. You can also email me direct through luke@simonorganics.com

      Thanks again for bringing this up.

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      1. The images on the USDA website could be wrong or the seeds may have been harvested or stored improperly. Environmental conditions or cleaning the seeds could change the color. The solution would be to grow a non arboretum collection here and then compare. I think I will try that. The USDA website is wrong once in a while, but it would take a god to change it and I am a peasant. When people contact my nursery and tell me I am off on a plant ID I ALWAYS assume I am wrong and look at the evidence all over again. Unfortunately the person giving me the information is ALWAYS correct and telling them otherwise is fruitless most of the time. I do not care what you publish and do not edit it. You might be right. For me the leaves and flowers match very closely so I am going to stick with my californication.

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        1. Demote yourself as you like. It seems you haven’t looked at much evidence, and denied what you have looked at. What is a credible source to you? There are several more websites with clear photos and suppliers (some I have purchased seed from) that assert fruticosa is what the USDA says it is -droves of pictures at Daves Garden (which is swamped with very credible, experienced, gardeners and botanists), Prairie Moon Nursery, Sheffield Seeds, and several others. Aside from looks, californica is not as hardy as fruticosa, only hardy to zone 6a, or -10 degrees farenheit according to several resources. My plants (seed from you, and a plant from you) have all made it through -20’s, two years in a row, without so much as dieback of the lignified branches. Californica can’t do that. Again, what is a credible source, because there are several. Whether you deny them or not, they all say you are selling fruticosa. Who cares what I say, just look at what they say. I simply point to the facts. Where are yours?

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          1. Gerd Krussmann Cultivated Broad-Leaved Trees & Shrubs Page 151. Flower and foliage match from on line images to our mature planting. Will look more closely to flower morphology this spring as this is the best way to separate highly similar species. In other news: I am still open minded.

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            1. Thankfully my friend was so gracious as to loan me all three volumes of Krussmans exhaustive work.

              I am a bit perplexed after reading it: it says fruticosa grows up to 3 meters, californica 1-2 meters. You said yours have reached 12-15 ft, which is even taller -probably due to the advanced age.

              Further, as I mentioned, californica is not hardy to the temperatures my plants have easily gone through without damage. I cited californica as hardy to zone 6, but Krussman cites californica as hardy to only zone 7 -even less hardy. He cites fruticosa as hardy to zone 5 -my zone.

              I’ll gladly compare my flowers later this year to what Krussman provides. It seems like straining out a gnat while swallowing (more than one) camel. You don’t have to be a botanist to see that.

              I am not a botanist so much as a student and designer of sustainable agriculture system. I value the success of my clients and my readers because we are all working together to realize a revolution of on-site fertility. For that, we need accurate ID. I am simply interested in providing accurate, truthful information about these plants. Are you?

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              1. Here is what I did: I went to a California native seed company site. The description there says the seeds are an olive gray or brown not red. I read about Amorpha and its geographical races. Although there are 12 species many of them are geographical races that are often indistinguishable from one another. At one time there were 4 species listed. I looked at the Wiki common images that all the seed companies use. Wiki common is not a place to do taxonomic comparisons. I looked up my original seed source. I trust that source completely and there is no reason to doubt it. Consider this-its an arboretum collection and most botanists would never trust the seedlings from that grouping because of a high probability of hybrids. They would want wild collected seed and rightly so. Arboretums frequently have genus’ lumped together making hybrids even more likely. This could also explain the hardiness factor. Although I have some oaks and baldcypress’s from southern Georgia and Alabama that are completely hardy here. There is a certain physiological hardiness with a lot of plants. I do remember one winter though where they did die to the ground. Our planting is in a very low area. I will try to get seed or plants of the California amorpha again this time from a wild form to make a comparison. Growing a species of Amorpha that is growing in a rocky canyon versus a rich topsoil will totally change the height and overall leaf and even flower characteristics. You have convinced me: for sure now I am not changing the species. In the history of Oikos Tree Crops there has been only one species change that someone id correctly and we were wrong. We immediately changed it.

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          2. “Botanists do not wish to go to heaven. All the trees there are properly named, properly labeled, and the botanist can’t tell God He is wrong-no fun for the botanists. Indeed that would be hell for them.” Tree Crops: A Permanent Agriculture by J Russell Smith.

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