If there’s one thing gardeners everywhere like to do, it’s grow things they shouldn’t be able to in their zone, and citrus is high on their wish lists. Unfortunately for most of us, citrus is out of reach unless you have a sunny indoor location and a large pot. Container citrus will never produce the quantities of a large outdoor tree. (When I lived in Southern California I had so many fruit in my backyard I used them to play catch with the dog.) But potted citrus can still produce high quality fruit and has intensely fragrant blossoms.
Outdoors, your options are very limited. The Trifoliate Orange (Citrus trifoliata), aka Hardy Orange, is almost never grown for its fruit in the United States, but can survive temperatures as low as -10F. Most commonly, it is grown as a sturdy hedge plant, and the widely available cultivar “Flying Dragon” grows in a fascinating corkscrew habit. When combined with long life, slow but dense growth and large curved thorns, it is a hedgerow that will withstand time, deer, and even cattle.
As a single shrub, it forms a roughly round to oval shape 10-15′ tall. It is most striking when the leaves drop in winter and reveal the twisted branches still festooned with orange, slightly fuzzy, fruit. When blooming in the spring, the flowers are as fragrant as any other citrus.
The fruit are edible… somewhat. They are not the juicy creations of modern plant breeding that have brought intense sweetness and seedlessness to the grocery store produce section. Reports online describe the fruit as intensely bitter or sour, sometimes say it is mildly toxic, and generally have nothing good to say about the fruit except that you can use the rind as you would any orange rind, and reluctantly admitting the fruit can be used for pectin.
So when my 4 year old tree, which isn’t even 4′ tall yet, produced its first fruit, I decided that in the interests of gardening curiosity, I had to give it a try.
Cutting into the fruit left a glue-like substance on my knife that was difficult to clean off. Dish soap had little effect on it; ultimately I just rubbed it off with a towel. The rind is thin and the flesh to seed ratio pretty close to 50:50.
Now came the moment of truth. I expected the taste to be awful. It wasn’t. No one is likely to want to sit down to a glass of the juice unsweetened, but the flavor was about as sour as a lemon with a hint of bitterness. The flavor did not have any particular likeness to other citrus, but perhaps grapefruit is the closest match. Just not as sweet.
Edible Landscaping has a recipe online for Orange Marmalade made with Trifoliate Orange. I haven’t tried it, as I only have the single fruit this year, but it reads like it would resemble a traditional English orange marmalade in taste.
I would not recommend this plant strictly for food production, but it could be a useful plant as part of an edible landscape, if for no other reason than as a source of pectin for the jams and jellies of other fruits.
I would think that, with careful breeding, this citrus family member could be bred for improved flavor and sugar content and fewer seeds. This is not likely to happen. It would take a lot of effort, and with ample parts of the world capable of producing better tasting commercial citrus already, the only audience for such a new breed would be home gardeners in zones 6 and 7.