Zeedman
Garden Master
This question comes up fairly often on garden forums, and you will likely get a lot of different answers. The funny thing is that depending upon where & how the beans are grown, and the pollinators present, there can be more than one "right" answer. Some can grow different beans side-by-side with little to no crossing, but IMO that should not be assumed to be the norm.How much do you folks pay attention to isolation distances when you're saving beans for replanting or sharing with the bean network? I used to pay very little attention but we have a lot of bumble bees and I started ending up with more and more out crosses. Now I think I've gone too far in the other direction and don't grow varieties that I'm saving anywhere near each other. I'm guessing there's a happy medium
Bumblebees are very active in my garden (there are nests on the property) so absent some form of isolation, crossing between two varieties of ANY species is likely. As an SSE member, I am growing beans to share, and some of those could not be easily replaced, if at all... so I probably use more separation than most here.
For seed saving of some self-pollinating crops (including beans & tomatoes) I utilize a combination of distance & barrier crops, as suggested by Dr. Jeff McCormack (of Southern Exposure Seed Exchange). Most of my beans are pole varieties; I plant them 20-30' apart, with trellises of other plants between. Trellises of limas, runner beans, cucumbers, and bitter melon make good barriers; I can only grow one of each species for seed saving, but may use 2-3 rows of the same variety in different locations. Fortunately we have friends who will gladly take all of that extra bitter melon.
Trellises of yardlong beans or climbing cowpeas too... but the beans are isolation for them, (rather than the other way around) since they tend to bloom too late to protect the beans.Pollen-rich flowers are also helpful between rows. At present, I use Zebrina flowering mallow, sunflowers, okra, or squash for that purpose. In the past, I've used cosmos & cleome, both of which self-seeded (as does the Zebrina currently). Unlike honeybees (which tend to follow a row of the same species) bumblebees work their way across the garden... so giving them places to "wipe their feet" reduces the amount of pollen they transfer row-to-row.
In practical terms, this means that I divide my gardens into zones, with only one bean (and one tomato) per zone. I also use a set of large pots along my front sidewalk, for irreplaceable beans that need extra isolation & TLC. This isolation strategy limits me to only 11-12 varieties per year (after our recent downsizing) but I've only observed 4-5 crosses in the last 15 years.
As @Bluejay77 mentioned, some varieties are more prone to crossing. Of the varieties I've grown, "Ma Williams" (a.k.a. Goose) and "Jimenez" fall in that category. I've had 2 crosses appear in "Ma Williams", and other gardeners have reported similar promiscuity in "Goose". A sample of "Jimenez" sent to me in trade one year was so heavily crossed, that hardly any of the 10 plants was the same, and the entire seed lot had to be discarded.
An SSE friend has reported heavy crossing in some of their greasy beans.Aside from distance & barriers, there are a few other ways to reduce the chance of crossing in saved seed. One of those is time isolation. Bush beans tend to flower earlier than pole beans; so if planted closely, you could save the first seed from the bush beans, the last seed from the pole beans, and both would likely be reasonably pure. You could also use what I would call "crowd" isolation... planting multiple small rows in lieu of one long row, and saving seed only from the center.
Last but not least, for the most irreplaceable heirlooms, you could bag a few blossoms. Bagging is the only way to be 100% certain of pure seed, if multiple varieties are grown in close proximity. The material used should allow free air flow, but be tight enough to exclude bees or other pollinators. The small mesh bags sold in craft shops work well, as do cut & tied pieces of floating row cover. I would not recommend covering beans completely with row cover. When I tried that with bush beans one year, they did not respond well... the plants became yellowed & sickly, and the cover had to be removed.
All of the above assumes that the purity of the saved seed matters; that seed will be shared with others as a named variety, or that the variety(s) being saved are rare and/or irreplaceable. If seed is being saved only for your own use, the small degree of crossing which may occur is nothing more than a mild inconvenience.
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