Oddly enough, I've seen bean varieties cross quite frequently. The problem was a combination of two droughty years and a huge population of bumblebees when the local honeybees died off. Lacking other food sources, the bumbles really worked over my well-mulched bean rows. Once they even managed to cross a P. vulgaris variety with a P. coccineus, which is supposed to be impossible! Fortunately, the cross usually shows up in the seeds, and I rogue them out. I've tried growing out a few of the most interesting crosses, but they were disappointing.
Then there are sports. Some bean varieties seem particularly prone to this; I guess it's why there are so many varieties of Black Valentine. In fact, I have a sport of this I think I'll grow out for a few seasons and see if it's stable.
Except in poor Allison's case---which is why I suggested that her seeds may have been mixed.
One way of controlling this is to always alternate light and dark varieties; say, a white and a red. Beans are an exception in that the seeds _are_ the fruit, and crosses show up when the current beans are ripe. So, if you alternate, and wind up with white beans that have red, or red ones that have white, then you know they are crossbred.
Of course, if you start with a red/white speckled bean...:-)
Ten feet separation is usually recommended for beans. But there are, as Ragamuffin points out, noteable exceptions. I usually grow beans with 20 feet separation, just to be on the safe side. Near as I can tell, haven't had any unwanted crosses yet.
I know this is an old thread, but everything old is new again in the garden and in the compost pile!
I moved to the desert a few years ago, and part of the plan is to move towards more organic and to start saving my own seed. One thing I noticed here in the desert is that the polinators are desparate for anything - I had no idea there were any insects besides scoripions and giant grass hoppers until my first garden here - many types of flies/wasps/bees and huge hawk moths. They are so happy to have an oasis here - but I am concerned about cross pollination. My veggie garden is 50 x 75 ft. My back yard is about 75 foot from the veggie garden. My question is - do you think 20 ft separation would be sufficient in my environment? I could grow one variety in the veggie garden area and one in the back yard and one in the front yard, I suppose, but it'd be easier if I could grow two types in the veggie patch.
Taking advise above, I will be growing a Kentucky Wonder Pole Bean, brown seeded, and a yellow wax bean that has white seeds for 2008.
Also, I will be growing black eye peas ( Vigna unguiculata) and have heard that they do not cross with the common bean (Phaseolus vulgaris). However, can someone tell me if V. unguiculata will cross with yard long beans (V. sesquipedalis)?
Sorry for so many questions. New at this :-) Thanks in advance for any help.