putting datepicker() on dynamically created elements – JQuery/JQueryUI

here is the trick:

$('body').on('focus',".datepicker_recurring_start", function(){
    $(this).datepicker();
});​

DEMO

The $('...selector..').on('..event..', '...another-selector...', ...callback...); syntax means:
Add a listener to ...selector.. (the body in our example) for the event ..event.. (‘focus’ in our example). For all the descendants of the matching nodes that matches the selector ...another-selector... (.datepicker_recurring_start in our example) , apply the event handler ...callback... (the inline function in our example)

See http://api.jquery.com/on/ and especially the section about “delegated events”