Atypical Ideas For Cold Weather Tropical Fruit Growing

I wanted to start a thread to discuss atypical methods of growing tropical fruit trees and other large plants outside of their normal temperature ranges. This is under the assumption that there is no cold hardy variety that could be grown instead.

Typical approaches I routinely see discussed for this situation would be to
• grow varieties in a greenhouse
• grow dwarf varieties in containers taken inside for winter
• covering the trees during the coldest weather
• heating the trees during the coldest weather

There are some inherent downsides to some of these ideas such as:
• routine maintenance (watering or placing/removing covers)
• requiring large dimensions (big trees = big covers/greenhouses)
• requiring very small trees (movable containers/small greenhouses)
• heating methods using energy/fuel (expensive if required routinely)

Although many people are happy with these normal ideas and do not consider the downsides a problem, I thought it would be good to get a collection of other ideas or ways to implement the normal ideas to avoid some of the typical downsides. I have brainstormed some out of the box ideas and thought I would share them so that I can get some feedback, as well as see if anyone had any other out of the box ideas. Any feedback is welcome.

The first idea was inspired by the citrus plants. Suppose you planted graft compatible but cold hardy plants (e.g. trifoliate orange) and grew them just outside of a small structure (e.g. greenhouse or cold frame). These plants would be allowed to grow like normal, except a few branches would be trained inside the structure and once inside would be top-grafted with more desirable varieties (e.g. lemons, oranges), espaliered on supports. The concept is that the plant would get all its nutrients from the cold hardy plant and root system which would be growing outside and therefore should require less intervention (e.g. watering) than a typical greenhouse grown plant. Theoretically the structure could be built like a greenhouse but have its roof removed seasonally for mild and hot weather, so used like a cold frame.

The advantages are not needing to routinely deal with watering and other chores typical with a greenhouse plant. The structure could be much smaller and better insulated than typical. Initial drawbacks I see are the complication of the idea, additional pruning for the basically espaliered inside varieties to keep them in the smaller area, and probably regular pruning of the outside plants to keep their size manageable.

Greenhouse In The Snow

I really love Russ Finch's geothermal greenhouses - I have this on my list for 'someday' when I can scrape enough money together to get one.

It's still an expense to set up, whether you buy the kit or build something like it yourself. He says it's about the same cost as setting up a conventional greenhouse, but once it's up he only pays about $1 per day for energy (to power a fan that cycles air through).

He's got beautiful citrus. In Nebraska!

In a climate that is usually amenable to the plants in question, but where the occasional freeze might otherwise kill them, consider a simple overhead sprinkler.  Left running all night or for the duration of the freezing weather, it will form ice all over the plant.  As long as water is in the process of turning into ice, the temperature of the whole thing won't go much below 32F/0C.  I have attached a sprinkler to the top of a tall bamboo pole to go up and over full size fruit trees this way....it is also a good thing to try for blossom protection on deciduous fruit.  The main danger is that in sever cold, the ice may get so heavy as to bend or break the branches, and if there are several consecutive nights of cold, the ground might get soggy from the excess water....which is also a problem for many kinds of trees.

Laura Overholt wrote:Greenhouse In The Snow

I really love Russ Finch's geothermal greenhouses - I have this on my list for 'someday' when I can scrape enough money together to get one.

It's still an expense to set up, whether you buy the kit or build something like it yourself. He says it's about the same cost as setting up a conventional greenhouse, but once it's up he only pays about $1 per day for energy (to power a fan that cycles air through).

He's got beautiful citrus. In Nebraska!

Thanks for the link, that was so interesting!
I did some googling as a consequence and found out that in the Netherlands about 4.5 % of the commercial greenhouses use geothermal heating, but mostly with deeper drill holes.

In Northern Germany the conditions seem to be more appropiate than here in the South due to the higher temperature of underground water flows. Looks like it is not used very often. But the article I found was about commercial greenhouses so probably this smaller setup would work? BTW, geothermal heating is increasing for newly built houses, even in my village.

For a greenhouse, a bigger hurdle than the initial expense in this country would be the cost of land. I will follow up on this technology however and hope it will spread!

This is probably relevant: https://www.lowtechmagazine.com/2020/04/fruit-trenches-cultivating-subtropical-plants-in-freezing-temperatures.html

my first year growing banana plants here in toronto canada.. i tried storing the plants dormant for the winter in the basement (2010)
unfortunately due to the basement flooding it did not turn out well
also i think the temperature was too high

ideally you dig them up in the fall and knock most of the dirt off the roots
let it dry out a bit and then keep it in a 10C dark dry place for the duration of winter
this year i tried the dormant storing thing again and i am fairly optimistic
i made a box out of foam and put a thermostat and a 5 gallon bucket with a fishtank heater in there
this is in an unheated garage.. here is a pic


if it works i will attempt to do this in zone 2
but with an earth insulated structure
i might use the cables they sell for keeping eaves from icing instead of the fishtank heater buried in some gravel/stone
i plan to have 4 solar panels arranged in a diamond shape on a post well above the ground
two steeply angled pointing up and two steeply angled pointing down
if the two pointing up are caked in snow hopefully the two pointing down will get the reflected light off the snow
the batteries and inverter will be in their own compartment within the shelter
if it is insulated with lots of earth it should not need to run often
might need a quarter full bucket with silica gel crystals to absorb excess moisture

i will still keep some baby banana plants inside my living space by a window just in case it fails

ideally the one up north i will use natural materials as much as possible other than the electronics and possibly a pond liner if i can not find enough clay to seal the roof

i have not tried this but many people who are growing palms out of their zone build an insulated box over them in the fall and they seem to do fine with the darkness/dormancy
it is possible many other plants would survive this as well although i cant say for sure which ones
if you have more than one... experiment

one issue way out of zone though is once you uncover it some cold weather could arrive again or just plain too cold in general for the plant
then you might need to consider an earth insulated or similar greenhouse

Plus4Zones Greenhouse - a guy in Quebec documented his experiments with greenhouses that culminated in an indoor orchard that he made out of a converted barn. Fascinating stuff. He's growing cherries, apricots, etc. in zone 4. I'm considering a similar idea for zone 7 and wondering now if I can grow citrus in an unheated greenhouse made from a converted commercial chicken house...they're a dime a dozen here!

as an update all of those banana pstems turned to mush
complete failure
not sure if it got too cold or was just plain too humid in there as i did not check all winter
i will be trying this again but following the recipe and storing them in a root cellar or something similar
on a posittive note i did have a banana (musa basjoo) survive the winter outside under a 1.5 to 2 foot layer of wood chips