Yes, you can grow citrus fruit outdoors in the open garden. Poncirus trifoliata sports large white flowers in spring followed by fruit that looks every bit like edible oranges in the fall. You can't eat them, but you can toss them around, and where they fall you are likely to get a cluster of hardy-orange seedlings. This is a plant you need to keep your distance from -- the thorns are vicious, and the plant is truly impenetrable. Even trimming it is very risky business. Poncirus, 'commonly' referred to as trifoliate orange or Japanese bitter orange, is very closely related to true Citrus and is used as rootstock in commercial orchards. The above photo was taken today.