One of the methods to increase rooting percentage of hardwood cuttings is temperature pre-treatment of cuttings; done after collection, but before the storage period.
Higher temperatures than those in cold store stimulate the development of callus and the formation of root initials (Hartman, Hansen, 1958; van de Pol, Vogelezang, 1983). Cuttings prepared in this way develop roots earlier and in greater number, but the effect of temperature depends on plant species (Whalley, 1979). In the experiment with Acer palmatum ‘Atropurpureum’, the best results were obtained with hardwood cuttings collected in November, kept at a temperature of 13°C for 3 weeks, and then at 2°C for 6 weeks.
Generally, with higher temperatures a shorter time of treatment is needed, lower temperatures gave a similar.
For Forsythia the best rooting stimulation was achieved with treatments at 17°C for 1 week or at 5°C for 2 weeks.
Weigela cuttings needed a lower level of the time-temperature factor.
Good rooting stimulation was achieved with treatments of 13°C for 1 week or 5°C for 2 weeks.
Greenhouse experiments with Acer, Forsythia and Weigela gave suggestions for field experiments with many other plant species.
It seems, that cutting response to temperature pre-treatment is connected with the plant species, requirements to starting growth in spring.
Plants beginning earlier, need a lower level of the time-temperature factor.