Abstract In a Lake States nursery, red pine, jack pine, white spruce, and yellow birch seedlings were grown from seed for two seasons in a plastic greenhouse under an extended growing season, and a season of normal length, both with and without supplemental heat. Seedlings in standard outdoor nursery beds served as controls. Greenhouse treatments increased germination and number of live seedlings of red pine and jack pine and the growth of red pine and white spruce. Supplemental heat did not appear to have any effect in the normal season treatment. Early results of an outplanting test indicate higher survival of white spruce and jack pine and a lower survival of red pine from the greenhouse treatments as compared to standard nursery stock. Seedling density and soil fertility should be studied in future trials.
Howard M. Phipps (Mon,) studied this question.