Get thee a Servo or two. They'll work nonstop. BTW, its quicker to send them to bed than to do a solar recharge.
o.O they can sleep to recharge energy? Man the things you find out by visiting this place.
A servo isn't a bad idea but there's still the problem of there being some 200 or so garden plots so i don't think a servo would manage to keep up, i'd probably need an army of them.