Seasonal frost tolerance of some ornamental, indigenous New Zealand plant species in the genera Astelia, Dicksonia, Leptospermum, Metrosideros, Phormium, Pittosporum, and Sophora

Abstract The frost hardiness temperature (i.e., the temperature that causes damage) and the lethal temperature (i.e., the temperature that causes death) were assessed in autumn (April-May), winter (July), spring (October), and summer (January) for 10 native plant species. The species in order of increasing winter hardiness/lethal temperature were Metrosideros kermadecensis and M. carminea ( — 3/ — 5°C), Sophora tetraptera and S. microphylla (-4/-6°C), Leptospermum scoparium (-5/-8°C), Sophora prostrata (-6/-11 °C), Dicksonia fibrosa ( — 8/-11 °C), Phormium spp. ( — 6/-11 °C), Astelia chathamica ( — 8/ — 11 °C), and Pittosporum tenuifolium ‘Irene Paterson’ (-9/ — 14°C). In summer, all species had frost hardiness temperatures between-2 and-5°C and lethal temperatures between-4 and — 9°C, except the two Metrosideros species where these temperatures were-1 and-2°C, respectively. No differences among cultivars of Leptospermum scoparium (°;Martinii’;, ‘Burgundy Queen’, and ‘Nanum Huia’) or Phormium spp. (‘Maori...