|Erythrina x bidwellii|
So when I was growing three more of them in pots at home, I did some research and noted they grow in the highveld which would experience freezing temperatures during winters. I also found out that they tend to grow in wet areas like ditches or near water. So I decided to experiment with one plant, placing it near the front wall of our house and covering it with dried grass and plastic for winter. We had a very cold winter, and despite the plastic the tuber was definitely wet during winter as the plastic did not stop water flowing downslope past the spot where it is planted. I saw a flower spike appear when the plant emerged but it aborted. Yet I did get to see the enormous leaves grow even larger and there were no spider mites to contend with. Inspired, I planted my two remaining plants in an area that has become my South African garden. While I have South African plants in every garden, this area is exclusively for African plants with rare exceptions (such as a Goodenia that was recently given to me and that has some cold hardiness but is from Australia). One of the plants flowered soon after planting and produced one large seed in a bean like pod. All three plants were planted so that the top of the lignotuber is several inches below the ground and a foot or more of bark chips were placed over them for this winter. I find that they can take lots of cold and wet but I am not sure if they can take deep freezing so I protect them in a way that should protect the lignotubers from deep frost. This spring all three came up, but only the one in front of the house decided to flower. It produced numerous spikes of vivid red flowers and, with hand pollination, is currently producing several pods of seeds.
More experience is needed growing this species outside of South Africa, and perhaps even in its native land. I wonder what exactly regulates flowering in this species. How much cold can it take during winter? I have heard that it did not survive in Raleigh North Carolina which has much milder winters than we do, but I imagine the extremely hot summers there might be too much for it. As far as I know no one else other than the person who tried it in NC is growing it in the eastern US and on a recent short trip to California it appears to either not be common or cultivated at all on the west coast. It is worth growing even for its foliage alone, and when the flowers do appear it is a visual treat. I have read that there are albino forms and hope that seed of these variations might one day become available.
I also grow another Erythrina right next to the wall, E. x bidwellii. This is a cross of two American species and it can die back to the root during cold. It needs a very protected spot and some mulch over it for winter in order to survive in NY. It produces long whip like stems with rather wicked thorns and long spikes of red flowers during the summer rather than right after it comes up as does E. zeyheri. It is also fairly brittle so the stems do break easily and are a bit unruly, at least for me. But in spite of these faults it does produce some really pretty flowers and is not particularly difficult to grow. I understand that it can become a small tree or large shrub in places like Texas and Florida where it does not die back to the roots.