%0 Articles %T Extension of the planting period of Norway spruce container seedlings: risks related to the drought – growth stage dynamics and handling practices %A Helenius, Pekka %D 2005 %J Dissertationes Forestales %V 2005 %N 3 %R doi:10.14214/df.3 %U http://dissertationesforestales.fi/article/1786 %X The first aim of this study was to investigate the possibility of extending the planting period of Picea abies container seedlings from May to June and July without risk of excessive mortality and growth restrictions due to drought. The second aim was to investigate risks related to thawing practices of frozen-stored seedlings. To achieve the first aim, 1.5-yr-old actively growing seedlings were exposed to different preplanting drying and postplanting drought periods. Seedlings kept dormant (sensu shoots not elongating) by prolonged frozen storage were also exposed to postplanting drought periods. To achieve the second aim, 1-yr-old frozen-stored seedlings were exposed to different thawing durations and temperatures before planting in mid-June. Height growth and root egress of actively growing seedlings planted in late June–early July decreased when exposed to postplanting drought as affected by the soil water content at planting and atmospheric evaporative demand during drought periods. Survival and growth under drought were also decreased by preplanting drying of root plugs and seedlings. However, mortality of actively growing, well-watered seedlings was negligible when exposed to drought periods not longer than 2 to 3 weeks. Prolonged frozen storage until late June had no observable negative effect on needle carbohydrate concentration and subsequent seedling outplanting performance. Contrary to actively growing seedlings, drought periods had no effect on root egress and chlorophyll fluorescence, and only moderate effect on xylem water potential of dormant seedlings. However, actively growing seedlings showed much greater root egress than dormant seedlings, except when exposed to very long (>= 3 weeks) drought periods after planting. Frozen-planting may adversely affect seedling performance at soil temperatures prevailing in Fennoscandia in spring or early summer, especially when soil is dry. Thawing over 4 to 8 days at 9-12 °C ensures complete thawing of the root plugs and unaffected field performance of frozen-stored seedlings.