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.
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.
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).