Poncirus citrus trifoliata - Flying Dragon
You can grow your own citrus even if you live where it snows.
Poncirus is a small, beautiful tree with multitudes of fragrant white flowers and tiny sour fruit that are used to make marmalade. The tree has an interesting crooked shape, grows only 8'-15' tall and makes a great ornamental houseplant.
And it's hardy to zone 5, maybe colder.
Poncirus is usually grown as root stock for commercial varieties. Its superior disease resistance, cold-hardiness, and miniature size makes it ideal for grafting, and its naturally contorted form for makes one extraordinary bonsai. Grow it indoors for the fragrant blossoms.