Updated: Sep 16, 2021
Every gardener likes a good growing challenge. Many of us, in our attempt to increase garden diversity, have been tempted to try growing more tropical plants in a not-so tropical growing zone. A fruit tree may be advertised to survive a certain temperature. But we wonder, does it really? Is it even worth trying to grow it for its fruit production?
I often find myself wanting to push the limits of my growing zone. For example, I am in zone 7b and technically there are some cold hardy citrus varieties that should survive reasonably cold weather. They may not survive northern winters, but 32 degrees fahrenheit should not be a problem for the survival of some of these varieties. Of course, we don’t just want survival, we want fruit production. How cool would it be to grow your own pomegranate?
There are some fringe plants that do much better in warm climates, but just might be able to hack it in a temperate zone.
Here are some of the fruits that come to mind - just to name a few:
Loquat (Eriobotrya japonica)
Kumquat (Citrus japonica syn. Fortunella obovata)
Calamondin (Citrofortunella microcarpa)
Yuzu Ichandrin (Citrus junos)
Other “cold hardy” citrus
Figs (ficus carica)-many varieties with varied cold tolerance
Cold hardy pomegranate (Punica granatum)
When I treat myself to one of these picky plants, I almost always start with them in a pot. I plant them in pots that are not smaller than 7 gallons, so they have room to grow for a year. 15 gallons would be more ideal. If I can plant them in larger pots, I do. I will leave these plants outside for most of the year- even when we have our first mild frost in the forecast. When temperatures start to look like they are getting closer to the plant's lower tolerance limit, I bring them inside. Ideally there is a sunny area inside, or a greenhouse, but most people don’t have the perfect south facing sunroom that is ideal. After the winter looks to be ending, I will pull them back out into the elements.
365 days later a whole new cycle of seasons has been completed and the plant that I originally bought is probably a little bigger - maybe it is even outgrowing its pot. At this point you will have a decision to make. Ideally, you have learned about the plant and understand its weaknesses and its tolerance for cold weather. There are two main choices at this point.
If you are still concerned about the plant and feel that you will be getting cold enough weather to kill it, you can keep it in a pot. You can bring it in again, or you can leave it in a greenhouse or a cheaper polytunnel or poly greenhouse. If you leave it outside or in a polytunnel, you should be checking the plant for cold damage as the weather gets cooler. You will lose leaves, but I'm talking about actual damage to the stem and other woody parts of the plant. For me, the polytunnel does a great job of protecting the potted trees that are not quite ready to go in the ground. I have mine against a south facing wall of my house. This builds up heat and holds a little of it through the cold night. Don’t forget - plants in pots that are left outside are MORE susceptible to freezing temperature damage because they do not have the insulation and temperature retention benefits from being partially buried in the ground.
The other option is to plant outside. This can be risky and may take more work. Many people actually use wool or fleece blankets to protect their cold sensitive trees. The more mature your tree is, the more it will be able to tolerate cold weather. If you plant the tree immediately after cold weather has passed, it will have all spring and summer to set down roots and become established. Different fruit varieties will take different amounts of time to establish. Fig trees can be very vigorous and set roots quickly while certain cold hardy pomegranates may take a while. Most importantly, find a warm microclimate spot in your yard for this tree. Again - this is probably the most important detail and is a whole other conversation for another time.
Every fruit variety will respond differently and will require different levels of care. Most of us don’t require that our trees produce a commercial sized load of fruit, but we would really like to harvest something at some point. The fig tree may establish quickly and may look great in the summer, but die back to the ground in the winter. As long as temperatures are reasonable, this should not be a problem - even if the fig tree dies back to the ground. A fig tree that dies to the ground will probably come back and may even produce some fruit in the upcoming season. The pomegranate, on the other hand, could also die back to the ground, but will not be able to grow fast enough to produce fruit. Citrus varieties will likely be a goner altogether.