I should add, so far we are thinking we'd cut food-grade 55-gallon barrels in half to put each tree in a 27 gallon container, under the cold frame.

We'll also probably utilize the shorter sides of the cold frame to grow seedligs in spring, and greens through parts of the winter.

Thanks!

Whatever it takes to keep them from freezing is in a nut shell all you need to do. I grow mine in containers in my greenhouse during winter.

Mike

I have a 20 by 30 hoophouse in zone 7b (Raleigh, NC) and my citrus do fine most of the time. I have two small electric heaters running most nights and when it calls for below freezing temps I use a wood burning stove. The wood stove can really crank out some heat but you have to baby it all night long - hopefully I will get better at it over time.

Some of the citrus decided to suffer this year (even though it has been mild so far) so I have rigged up a tent inside the hoophouse, a sort of greenhouse inside a greenhouse. I put one of the electric heaters in it and run it all the time - so far it seems to be helping.

You could partition off sections of your structure so that one section is super heated while others are not and keep the really delicate stuff in that section.

Heating the hoophouse is not the problem. Keeping the heat inside is the big problem. Plastic sheeting just doesn't hold on to heat very well.

You can allow things to cool down to the point where your plants go dormant and then you can lower the light levels by covering the structure with a pool cover or other sort of thermal covering. You can eventually get the covering built up to the point that the whole thing keeps itself warm - but you won't have much light which the plants need to stay active. But by encouraging them to go dormant (dry, cool and dark) you won't have to do much work and often they survive til things warm up in the spring. All of this falls apart if you want to grow crops at the same time. If you increase the light levels enough to encourage growth then you have to keep the space much warmer.

I have all sorts of citrus and they do not always follow the rules - some that are supposed to be delicate have no problem with winter cold while some that are supposed to winter hardy almost die each year. Some do fine for years and then all of a sudden go downhill, so you have to be flexible.

It can be done, but it does require a bit of planning and work. If it was easy, everyone would have citrus in their gardens.

It would work so long as you provide adequate heat and properly vent it so that, paradoxically, it does not overheat on sunny days.

Strings of 100w or C9 Christmas lights would probably do the trick. I have also seen where people use small ceramic heaters or aquarium heaters in buckets of water.