Gnomes is the "official class name" for the dwarfs with long lived woody stems, as there are also classes of dwarfs without woody stems. For most, to keep the woody stems through the winter, they need to be kept nearly frost free. I know they're root hardy to zone 7 or so, but the woody trunks need to be kept above freezing, or if they do get a freeze, they should be relatively dry,. Dry and cold is near impossible especially since the roots need to be at least lightly moist. So best to keep above freezing. Key is winter should be cool, and should have less than 10 hours of sun. No lights to interrupt the 14 hour dark period. Length of darkness can be longer, not shorter. This will keep them dormant.
When you want growth, increase day length. Bloom induction begins with shortening day length in autumn.
