Green beans, Dry beans, and cross-polination

Hi all.

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.

Thanks in advance for any advice!

Depending on when they all flower. Yet I think they may cross pollinate.

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.

Thanks for the tips from practical experience, Joseph!

Joseph Lofthouse wrote: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.

After having read so many conflicting opinions on a search for Phaseolus cross pollination distance, I'm quite glad to find this Lofthouse opinion. Hoping to grow a landrace and at least one heirloom variety of dry bean, if not multiple and maintain the heirloom(s), in land I may have an opportunity to begin stewarding/market gardening in. I am in a very humid region that will likely have LOTS of bees, so a good distance will be made between any cultivars I want to keep isolated. I am curious if large numbers of other flowers between the plants would reduce the distance needed or not? (lets say a good number of coriander and dill flowers for example? or even other genus of legume in between.)

sam mintgreen wrote:
After having read so many conflicting opinions on a search for Phaseolus cross pollination distance, I'm quite glad to find this Lofthouse opinion. Hoping to grow a landrace and at least one heirloom variety of dry bean, if not multiple and maintain the heirloom(s), in land I may have an opportunity to begin stewarding/market gardening in. I am in a very humid region that will likely have LOTS of bees, so a good distance will be made between any cultivars I want to keep isolated. I am curious if large numbers of other flowers between the plants would reduce the distance needed or not? (lets say a good number of coriander and dill flowers for example? or even other genus of legume in between.)

I maintain a number of "heirloom" varieties of beans as well a a number of different landrace collections in my gardens, it is not difficult to do with just a little attention to isolation.

In "Seed to Seed" by Suzan Ashworth she describes bean flowers as being closed and generally self pollinated before the flower even opens. However bees, especially larger bumblebees are able to open the flowers and spread pollen. I am lucky to have a nice assortment of such bees and work with them to cross or not cross my beans as desired. If for example in my KY Wonder beans that we use for green beans and the woman here insists are not mixed up I just plant them by themselves separated a little  from other beans.

I have watched the bees and they are very methodical in their foraging, going from one flower to the next closest one. Even a short distance between varieties and or other flowering plants between will reduce chances of cross pollination to near zero. In the case of beans grown for eating green even if a cross did occur it is most likely I will never know it. If the even lower chance that a crossed seed from the green bean patch is accidentally saved and planted the next year it is not a serious issue as far as contaminating the overall seed stock of that variety.

I grow mostly pole beans and generally select my seed from individual pods instead of mixing up the whole patch. That is as the pods start drying I watch and collect the best pods one at a time. Say the variety I'm preserving has long flat pods, I just make sure any other pod type that might be in that patch isn't saved with that varieties' seed. Sam if the seeds are a different color or shape. Instead those seed, assumed to be a cross, are added to one of the landrace collections.

Over in the landrace plantings where I want to encourage maxim crossing I just plant different seeds immediately adjacent to one another. If two different pole bean plants are sharing the same string in the trellis the flowers can be so intermingled and close to together that the bees can easily do a back and forth this one to that one thing just in their normal, closest to closest routine. Crossing has become very common in my dry bean landraces.

Why do I have more than one dry bean landrace? I'm working to create a landrace of "semi" vining beans. That is that they do climb but only to 6 feet or so instead of the giant vines of my old collection. My new semi vining type isn't diverse or productive enough yet to replace the old giant vine collection so for now I have both. I also grow bush beans in association with both pole types and include or cull appropriately any new ones that show up.

In last few years I have been selecting for early maturity of dry beans. Beans that are actually at dry down stage in less than 100 days. This year that day passed on August 14 and I have about 3 pounds of seeds that dried by that time. I also have at least 5 new beans in that group.