(436) Comparative Cold Hardiness and Freezing Behavior of Leaves, Buds, and Flowers in Selected Woody Plants in Northern Latitudes

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  • 1 The Morton Arboretum, Urban Horticulture Lab., Lisle, IL, 60532

It is not well known how cold-hardy new buds and emerging leaves or flowers are during spring. Extreme temperature fluctuations that sometimes bring early frost in spring (April–May) are very common in northern latitudes and cause severe damage to emerging leaves and flowers. Even though most woody plants can tolerate frost in spring, others show early tissue damage and can fully recover. There are some trees, e.g., Japanese maples (Acer palmatum) that when leaves are damaged due to spring frost, the results include severe dieback and eventual death. We tested new flowers and leaves of four crabapples: Malus ×micromalus, M. sargentii, `Mary Potter', and M. hupehensis, after budbreak for 3 years using electrical conductivity (EC) and differential thermal analysis (DTA) in spring: May 1997, Apr. 1998, and Apr. 2000, at The Morton Arboretum. Both flowers and leaves can tolerate from –6 to –12 °C and we observed higher ion leakage in leaves than flowers. The high temperature exotherm (HTE) of flowers were –8 to –10 °C in April. In a companion study, testing other species that had premature budbreak due to “near lethal” (sublethal) freezing stress in Jan. 2001, the following HTE were observed: Cornelian cherry (Cornus mas) flower (about –7.5 °C), Spindle trees leaves (about –6 °C), Judd's viburnum (Viburnum ×juddii) (about –8 °C), Brevipetala witch-hazel (Hamamelis mollis`Brevipetala') flower (about –5 °C), redbud (Cercis candensis) flower (about –9 °C), flowering quince (Chaenomeles ×superba) flower (–8 °C). Multiple LTE at –13, –18, –22, and –27 °C were observed for Judd's viburnum. This information could be useful for selection and breeding of woody plants.

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