This past year, I ordered and planted Lofthouse Dry Bush Beans - they are growing well, and I'm looking forward to harvesting (and saving) them this year!
However, I also have planted several varieties of beans that are intended as green beans in close proximity, and I was considering doing more. I have 5-6 varieties of green beans in various left over packets from previous years, and I was just going to plant them all. My hope is to never buy bean seed again.
However, I'd love to maintain both a dry bean population and a green bean population, so this leads me to a few questions:
1. I've never grown dry beans before. Will cross polination between green and dry beans 'ruin' both varieties?
2. How common is inter-plant polination? Looking at Josephs dry bean cultivar, it appears that there are a consistent 5-10 separate phenotypes of bean from year to year. Does this mean that most polination is self-polination?
3. How would you select within these two populations to help keep my green beans crunch and edible in their stage, and the dry beans consistent with their properties for storage and cooking?
With better planning, I would have at least grown them on separate ends of the garden to open up some space in between, but... I didn't.
They may cross some. It may not be a bad thing....you won't really know until you see how good the green beans are as dry beans and vice versa. I don't know that being good for either purpose needs to be mutually exclusive.
The conventional wisdom regarding beans, is that they only need to be planted far enough apart to avoid mechanical mixing. Say around ten feet. I recommend more than that.
Depending on ecosystem, beans cross pollinate at a rate of 0.5% to 5%. More humid climates with lots of carpenter bees may have cross pollination rates as high as 20%.
If green beans cross with dry beans, the pods become fibrous, so they are not nice for fresh eating, and the pods become hard to thresh. They are still good for eating as dry beans, just more work to clean the seeds.
One of my selection criteria for dry beans is easy threshing, so if green beans ever got mixed in with then, the trait would be self-eliminating because I only save seeds from easy threshing varieties.
Likewise, if I were maintaining a green-bean landrace next to a dry bean landrace, I would pick them by snapping the seed pod. If a pod didn't snap easily, I'd cull the plant right then.
If green beans cross with green beans, no worries, they will retain the non-fibrous pod.
My dry bush beans have around 70 phenotypes that I can identify with my eyes. I intend to plant all phenotypes every year.
If the dry beans and the bush beans are grown on opposite edges of the garden, they will mostly stay isolated.