Hereroa incurva is a night blooming species with wonderful smells of candy and other sweet aromas. Stems can turn bright red in winter or summer when the plants are being stressed, this can be quite colorful. Plants can bloom multiple times in a year and commonly bloom when nights are around freezing. These have survived our garden taking -8F with snow cover and -2F with no cover at all. Worth a try if you have a cold hardy rock garden.
I do not guarantee these in a zone 5/6/7 because everyones growing conditions are different but this would be a good trial plant to grow in your cold outdoor garden. Try to plant outdoor 90 days before 1st hard freeze.