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Cold-hardiness of Containerized Loblolly Pine Seedlings

Mexal, J. G., Timmis, R., and Morris, W. G. Southern Journal of Applied Forestry 3(1):15-19. 1979.

Loblolly pine seedlings grown in the greenhouse for· 92 days in 64 ml Leach cells were hardened outdoors for 0, 14, 28, or 42 days. Those seedlings outplanted in November after cold-hardening for 14 days did not survive temperatures below -4°C (25'F). Seedlings cold-hardened for 42 days were hardier and their survival and height growth better the following season than trees hardened for 14 days or less. Seedlings kept in the greenhouse under an 8-hour photoperiod survived as well as seedlings hardened outdoors during a 42-days period. But seedlings held in the greenhouse under the natural photoperiod ( =11.5 hours) were unable to survive temperatures below -6"C (21'F). Results suggest that a short photoperiod may be substituted for cold temperatures to induce hardiness. For a successful fall planting of containerized seedlings, seedlings must be cold-hardened for at least 42 days, either outdoors or under shortened photoperiod.


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Author(s): John G. Mexal, Roger Timmis, William G. Morris

Section: Seedling Physiology and Morphology

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