Onion on a Spring

Seriously, it's more than just a pun on Spring Onions. You see, onions grow underground, don't they? Or even if they don't, they grow lower down than most people would normally have their hands on passing by. And I know many people who've gone mad about how, during onion picking sessions in the summer, they've developed the most terrible, life-threatening backache. So what you do is you genetically engineer an onion that projects a spring down towards the Earth's corewards as it grows up. And as it gets older still, chemical energy transmitted down the spring makes it 'wind up' - by a process not dissimilar in fact to reverse osmosis. By the time it's ripe, the spring will be somewhere way down below, and fully wound up. As some suffering back-person walks by, therefore, the spring fires (bang, boing) and projects a perfectly formed onion into the air, requiring only a deft catching in the basket of the peripatetic labourer.

Of course the spring must be self-detaching - and yes, it would be. Plastic might be best for this.