Pollen is microscopic and drifts on the wind or rides in on an insect’s legs, which is how a carefully saved seed comes up unlike its parent. Distance, a fine-mesh net over a flowering tree, a thick hedge, pollen-free triploid varieties or simply growing one variety at a time will all keep two varieties apart.
Pollen may travel far, but in many cases having several hundred yards or meters distance will already significantly reduce pollination.
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.
Each barrier works on a different carrier of pollen — wind, insects or the flower itself. Pick the one that matches your garden’s size and what you are trying to protect.
| Method | How it works | Effect on pollen | Best suited to |
|---|---|---|---|
| Greater distance | Several hundred yards or metres between the two varieties | Significantly reduces pollination | Seed growers keeping a variety true |
| Separation in time | One variety this year, the other the next | The two can never meet in flower | Gardens with no room for distance |
| Fine-mesh net | Wrapped around the tree while it flowers | Stops insects and wind-borne pollen | A single fruit tree |
| Closed greenhouse | Plant grown where outside insects cannot enter | Blocks cross-pollination entirely | One special variety worth protecting |
| Hedge or wall | Thick screen set between two varieties | Halves the distance pollen travels | Neighbouring beds and rows |
| Pollen-free varieties | Triploid cultivars bear no pollen | Nothing to give; fruit tends to be seedless | Apple and pear growers, bee allergies |
| Removing flowers | Male flowers cut from the mother plant | Only the chosen father’s pollen arrives | Producing a very specific hybrid |
Combining two of them — a hedge plus extra distance, or a net plus a pollen-free variety — is more reliable than trusting any single barrier.
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.
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.
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.
For apples and pears, for instance, varieties known to be “triploid” won’t bear any pollen at all.
Examples of triploid apple varieties:
For pears, triploid varieties include:
Gardens with poor pollinators will not be attractive to pollinating insects. In general, such trees and vegetables will tend to have seedless fruits.
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:
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
