While it’s difficult to keep microscopic pollen from flying around, there are a few things that will reduce cross-pollination.
- Quick read: what is cross-pollination?
- Promote cross-pollination instead of blocking it
- All our posts to understand cross-pollination
Increase distance to other varieties
Pollen may travel far, but in many cases having several hundred yards or meters distance will already significantly reduce pollination.
- This explains why for certain crops to be certified as non-GMO (genetically modified organism), distance is a critical parameter. The grower has to prove that the nearest GMO field of the same species is at least several miles or kilometers away. Distance greatly reduces cross-pollination. Minimum distances are sometimes regulated by certification or government agencies.
- Seed growers are especially careful to avoid cross-pollination so that offspring remain true to the original variety. They often have fields that are at great distances from one another.
The greatest possible distance isn’t even in miles or kilometers: it’s time! Sometimes it’s best to only grow a single variety, and the following year to grow another. That way, you’re sure that the two won’t cross-pollinate. Seeds are usually viable for several years, so it won’t compromise your ability to grow.
Keep pollinating insects away
A net with fine mesh wrapped around a blooming tree will keep insects from bringing foreign pollen in. You only need the net during the blooming period. It also acts as an obstacle to wind-borne pollen.
You might also want to grow your special plant variety in a greenhouse that is closed to outside insects instead. This should block cross-pollination entirely.
Set up obstacles
Even simply setting up a garden hedge or wall will reduce the amount of pollen carried over by air and insects to prevent cross-pollination.
- Continuous hedges cut pollination distance by half.
- This means you can reduce the buffer distance by half by growing a thick hedge between two plant species or varieties you don’t want cross-pollinating.
Grow varieties that bear little pollen
Some varieties are known to be excellent pollinators while others produce little pollen, poor pollinators. Steer away from excellent pollinators if you fear your trees would get damage from over-pollination.
Apple & pear varieties that bear no pollen
For apples and pears, for instance, varieties known to be “triploid” won’t bear any pollen at all.
Examples of triploid apple varieties:
- Baldwin
- Belle de Boskoop,
- Blenheim Orange,
- Bramley’s Seedling,
- Calville Blanc D’Hiver,
- Cat’s head,
- Gravenstein,
- Holstein,
- Jonagold,
- Mutsu,
- Ribston Pippin,
- Stayman winesap,
- and Winesap
For pears, triploid varieties include:
- Belle Angevine,
- Beurré Alexandre Lucas,
- Catillac,
- Merton Pride,
- and Vicar of Winkfield
Gardens with poor pollinators will not be attractive to pollinating insects. In general, such trees and vegetables will tend to have seedless fruits.
- If you’re severely allergic to bees, consider planting only plants that are poor pollinators. This will reduce the risk of having unintended bees buzzing around. Not to mention, less hay-fever triggering plants.
Cut and remove undesirable flowers
This solution is often implemented when trying to produce a very specific hybrid.
For example, most of today’s corn (maize) are hybrid seeds. These are a cross-breed between two different corn parents. One must be the mother, and the other a father: if their roles were reversed, the hybrid offspring would not be the one sought. In this case, since corn has both female and male flowers, the following is done:
- Male flowers on the “mother” plant are removed before they can mature.
- This ensures that only male pollen from the correct “father” plant reaches the female flowers.
- Rows of “father” stalks are destroyed after pollination and fruit set so there’s no point in removing flowers from them.
It’s time-consuming work but the hybrid seed sells well: it produces a more vigorous plant than either mother or father plant!
→ Refresher: what is cross pollination
→ Opposites attract: how to increase cross-pollination
CC BY 2.0: Apple and Pear Australia Ltd, Katina Rogers
CC BY-SA 2.0: Alexander van Loon
Is cross-polination with various types e g. Black beans, white kidney beans and speckled beans going to create a problematic crop? I planted these 3 together and only realised later that it could lead to a possibly useless crop. Kindly advise
Hello Henri, for the current crop it isn’t a problem at all. Cross-pollination between 2 different varieties is actually going to make each seed stronger and more viable. So your seeds will all take after each of the mother plants for this harvest.
However, for the next generation, the genetics will be mixed up. This means that you won’t have “pure” varieties anymore. If you sow the beans, even if the seed looked like a black bean, what might come out from that particular plant will be a one-in-three chance of being A) pure, B) a black & white bean hybrid or C) a black and speckled bean hybrid.
You can’t really control this easily, unless you use netting to segregate pollinators, or plant them at great distance.
So for seed consumption, it isn’t useless at all, quite the opposite. But for propagating seed varieties, it is indeed going to be useless in that you don’t know what to expect for the following harvests.
There is a slight chance that you’ll be positively surprised, though: some hybrids will have the best of both parents!
Dear Gaspard, thank you so much for your response. Am I correct in that all dry beans (e.g. black bean, kidney bean, speckled bean and so on) are of the same variety and will therefore not cross-pollinate?
Sorry for such a dumb question but if one do not know what is the solution?
We once grew water melon and butternut not very far apart and the next season some strange looking round things came up that was not edible (in our opinion) so are now rather safe than sorry
Thank you for your time!
Kind regards
Henri
Hello Henri, to be clear, you are incorrect: all your beans are different varieties, but they are the same species: they will most certainly cross-pollinate!
It’s ok it isn’t a dumb question (dumb questions are those not asked!). There are several options to avoid cross-pollination among your beans, but since they’re already planted you’ll only have a few to chose from: setting up nets or wind-breakers between the different varieties will significantly block pollinators from mixing the pollens up.
I understand you were surprised with your watermelon and butternut, but it’s technically impossible for them to cross-breed: they’re as different as cats and dogs! What might have happened is that they were crossed with another watermelon, or squash, from somewhere else.
Even more probable is that these were hybrids to begin with (seeds sold with “F1” in their name). These never reproduce true to parent, and generally degrade into weird, strange fruits that are themselves even more prone to being sterile. Seed manufacturers love these kinds of hybrids because they guarantee that farmers will buy seeds in the following years…
Hope this helps, you’re very welcome!
Gaspard