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Proceedings of Past Forest Nursery Association Meetings:

Producing Blue Oak Seedlings: Comparing Mini-Plug Transplants to Standard Bareroot and Container Stock
Doug McCreary and Laurie Lippitt
1996: New England, CT
Blue oak (Quercus douglasii) is one of several species of native California oaks that is reported to be regenerating poorly in portions of the state. Although blue oak has little commercial value other than for firewood, it provides vital habitat for numerous wildlife species and is highly valued for aesthetics. In the last decade there have been efforts to develop techniques to successfully regenerate this species artificially. Procedures for growing both bareroot and container seedlings have been evaluated in research trials and both stock types have been grown and outplanted operationally. While both bareroot and container plants have performed adequately in the field, we were interested in evaluating a relatively new stock type called a "miniplug transplant". These are seedlings that are grown for several months in relatively small, shallow containers , and then transplanted to bareroot nursery beds in the spring. While in the containers, seedling roots grow rapidly, but due to the shallow container depth, they repeatedly air prune themselves. As a result, a highly branched root system, with numerous growing tips, develops. When these mini-plugs are transplanted to a bareroot bed, they often develop a more fibrous root system and a more favorable shoot/root ratio than conventional stock types grown for the same length of time. As such, they may be better able to survive and grow in the hot, dry summers characteristic of California's blue oak woodlands. This study was undertaken to evaluate the mini-plug approach for growing blue oak seedlings, and compare the field performance of this stock type to 1+0 container seedlings and conventional 1+0 and 2+0 bareroot nursery stock.

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