Citrus reticulata tangerine A comparatively cold hardy citrus, with selections that are reliably cold hardy into zone 8. They should be grafted onto trifoliate orange root stock for maximum cold hardiness. Plants so grafted are reported to be shorter in stature. Grow these trees in sunny, well-drained sites. 'Flying Dragon' rootstock, for example, is vigorous, cold hardy and has a dwarfing effect that helps keep trees at pick-able heights.