>>979614Doesn't really matter too much for peaches. Most full sizes only get around 10-16 feet tall anyways,where as a dwarfing one might get 8-10.
It's not like apple trees where it's the difference between an 8 foot tree or a 35 foot tree.
>>979695You might want to look into the kind of stuff used for solar water heating or solar pool heating. You can get the equivalent of several KW of electric heat for pretty cheap(electrically speaking,the equipment and install still costs money).
A simpler and easier way would be insulating the tanks pretty well and allowing light in to hit something darkly colored so it absorbs heat during the way.
Plenty of people use things like 55 gallon drums painted blank filled with sand or water to help keep greenhouses warm during winter. Just have to store that thermal energy somehow,and water is actually a very good way to do that.
