Citrus Zone 6 . Warmth is critical to successfully growing citrus trees in a greenhouse during winter. Zone 6, also known as mars (formerly asteroid), is a zone in jtoh and the sixth zone in the spatial system. Growing Citrus in Zone 6 YouTube from www.youtube.com Warmth is critical to successfully growing citrus trees in a greenhouse during winter. Ornamental grasses for zone 6. Comprises counties, or portions of counties, that are generally infested with acp, hlb has been detected in some areas, a geographical barrier exists between it and adjacent contiguous citrus growing regions (i.e., zones 2, 4, and 5), a contiguous citrus growing region exists within the zone, sufficient citrus commodity cleaning and.