Luoranen, J., Zhang, G. and Smolander, H. 2005. Production of even-sized hybrid aspen plants from root cuttings: transplanting, height grading and planting dates. Baltic Forestry, 11 (2): 20-28

At present in Finnish nurseries, hybrid aspens are reproduced from root cuttings by transplanting the sprouted cuttings to the large plugs (trays with 380-400 cm3 cell volume). Sprouting time of cuttings varies within and between clones a lot. This causes problems in the production of aspen plants: the large height variation within a plant batch in nurseries and the high proportion of short plants (with minimum height of 40 cm). To produce more even-sized batches, plants were graded into height categories twice: first when transplanted them into small plugs and then into larger plugs. This procedure reduced the variation in the final height of graded batches in comparison with the batches transplanted directly into the large-volume containers. The variation in the height of hybrid aspens did not exceed the variation in a reference silver birch batch, however. The use of short plants for plug-to-plug transplanting changed the growth rhythm of the plants, resulting in later cessation of the height growth. One solution to the problems is to plant hybrid aspens in summer at the time of plug-to-plug transplanting. The height growth of these plants increased and the shoot tip dieback inhibited in comparison with plants that were grown for a longer period in the nursery, frozen-stored and then planted in the spring or early summer of the following year.

Key words: grading, height, hybrid aspen, planting, Populus, root cutting