What to Do with Bean Crosses

Bean crosses, crossed seed, saving bean seed, dealing with crossed bean seed

Beans are probably the main crop which introduces gardeners to seed saving. They show a wonderful diversity in every way imaginable. Some beans have stunningly attractive seed, but bean crosses do sometimes turn up. A cross occurs when one variety of bean cross pollinates another. Some seed saving resources say that bean crosses are rare. Under certain circumstances bean crosses may be fairly uncommon, but even a few if not dealt with can corrupt and, eventually destroy a good line of seed. I’ve heard a number of accounts of rare varieties being lost to crossing.

What factors affect cross pollination in beans?

  • The #1 reason beans cross is that varieties are grown too close to one another. When I first started saving bean seed I thought 15′ distance between varieties was enough. In the last decade, however, I’ve seen crosses occur from as far away as 40.’
  • The presence of bumble bees and other kinds of solitary bees. Some solitary bees are really tiny and easily mistaken for some kind of fly. But they work the flowers, spreading pollen between bean plants. I suspect that native bee (solitary bee) populations may be increasing in my area, which is actually a good thing; just not good for preventing bean crosses.
  • Heat and drought increase cross pollination in beans. This is because the stress causes bean flowers to open wider, allowing more and easier cross pollination.
native bee, solitary bee, crossing of beans, bean cross pollination
Native bees come in different sizes.

We’ll deal with preventing crosses in another post. The best way to prevent crosses is to keep varieties separated by time or space. Barrier crops, planted between them, especially tall crops which produce flowers, can help.

How does one know when their bean seed has been crossed?

First of all, understand that the season a cross first occurs it will be undetectable. A cross pollination of seed will not affect the color of your seed, shape or quality of the pods. That will come next year.

A cross may result in any of the following changes in offspring characteristics:

  • Growth habit of the plant (bush or climbing)
  • Color of flowers
  • Change in shape, color or texture of pods
  • Change in color, size or shape of seed
  • All of the above
  • Characteristics unseen in either parent strain may crop up in a cross, especially in the second grow out (F2 generation).
crossed beans, crossing in beans, cross pollinated beans
A violet flower in a planting of beans which normally have white flowers, indicates a cross pollination the year before.

A cross’s first generation seed (called F1 generation) will produce a uniform offspring. The second and third generation (F2 & F3) will explode into a diverse mix of characteristics, some unanticipated.

See Green Country Seed Savers for some Additional tips on saving pure seed

So What Does One Do Upon Discovering a Cross?

There are several possible ways to procede:

Decide if you want to maintain pure seed or not. For some, this is important. For others, it is not. If you want to maintain pure seed…

  1. You may try selecting  seed from only the plants which exhibit characteristics of the variety you are trying to grow. With luck, that may be the end of it. If you’re not so lucky, it may take a couple of  years to cull the undesirable cross. It can be done.
  2. Go back to an earlier batch of seed for next year’s planting. Try planting seed from two years earlier and see if it pure. If it is, discard the tainted seed and keep the pure.
  3. Purchase or request new seed from a trusted source.

For further reading: Quick Tips For Saving Bean Seed



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