Why would you want to? Well, I'm thinking that it might be fun for those who want to try breeding their own unique varieties. Also, as it's fairly easy to do, it would make a good starter project for anyone who wants to try out hand-pollination for the first time.
I'm not providing any information on sweet pea genes here ... and that's because I don't know anything. So if you want to try it it'll just be a case of breeding two different things together and seeing what happens. But that's all part of the fun. Try cross-pollinating plants with very different flower colours and see what you end up with.
Hand-pollinating sweet peas is exactly the same method as for culinary peas (which I covered in detail in another post), except that it's a lot easier because the buds are bigger and easier to open and the stigma is so huge you can't miss it. The only bit that's slightly tricky is making sure you choose buds at the right stage. Sweet peas are inbreeders and are very efficient at self-pollinating while the buds are still quite young. To make a cross, you have to catch them just before they self-pollinate and remove the anthers (emasculation). Luckily the anthers in sweet peas are large and easy to pull off.
The lower bud is at the right stage for hand-pollination. The petals are just starting to emerge from the sepals (that's the outer bit that looks like a little green pixie hat) but haven't really started to develop their colour yet.
This is the same bud with the outer petals folded back and the inner keel petal removed. You will find a long green pokey thing (style) with a receptive tip (stigma), plus ten yellow anthers. Check that the anthers have not yet begun to shed pollen (if they have it's too late) and carefully remove them all with a scalpel blade.
Now collect some fresh pollen from the donor plant ... a bud that has just opened is usually ideal. Collect it on the blade of the scalpel and then carefully dab it onto the stigma of the first bud. The stigma is right at the very tip of the green pointy thing. You should see the grains of pollen sticking to it when you've done it right. Then just fold the petals back into place and let nature do the rest.
Don't forget to mark the pollinated bud though (I usually tie coloured threads round them) or you'll never find it again!
(With thanks to my husband Ian for the loan of his fingers in this photoshoot)