Certain insects help take pollen (mating substance) to another plant of the same species, and their mating pollen mixes and helps fertilise the plant.
In the same way that mammals use sperm to fertilise eggs, it is the same system, but plants cant move to have sex. So some insects do it for them.
In some poly tunnels, it may be that humans use earbuds or similar items to make sure that plants mate.
Edit: also the wind and crawling bugs can create the same way of plants mixing their important breeding parts.
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