i live in zone 6 (Ohio) and really want to have a completely outdoors area where the the soil stays warm for a longer time than it normally does here. i don't want to use a greenhouse, because it's very important to me to maintain complete animal access to the area. i'm in the process of planning out a series of hugelbeds and swales for a hillside, and my hope is to incorporate a rocket-mass heater into one of the hugelbeds and light it up as needed during either end of the growing season. i'm not sure what all would end up going in this area, but it's 99% motivated by sweet potatoes. i know there are many things to consider, such as how deep i place the heater, how deep the bed itself is, how wide and long the bed is, how to waterproof the heater, etc, but i can adjust all of that as needed.
so, if constructed optimally and monitored daily, could such a bed have an extended growing season? heated beds seem to be more common inside of greenhouses, so is placing one outdoors even practical? would too much of the heat dissipate to the area around the bed?