The experience you had rooting prunus cuttings is usual. While you did not
use a plant rooting hormones like Rhizopon AA Water Soluble Tablets before
the winter the results are the same like described:
IBA USED FOR ROOTING OF CUTTINGS BY IMMERSION
The IBA Immerse method is suited to hard to root plants. It is used to root
prunus rootstocks, evergreen. deciduous shrubs. conifers. platanus
acerifolia (London plane) (Macdonald. 1986. ill.: pg. 345-346). Immerse the
basal ends of the cuttings approximately one inch in solution for 4-12
hours. For cuttings propagated under mist the treatment is a maximum of tour
hours. The cuttings are planted immediately after treatment. For woody and
herbaceous cuttings use 50-150 ppm IBA dissolved in water.
Eropean growers have for over fifty years used the IBA Immerse method to
root cuttings of prunus rootstocks including St. Julien (plum and other
stone fruit, etc.). In the Autumn sixteen inch cuttings are taken from the
parent plant. Basal ends of the cuttings are Immersed in 100 ppm IBA
dissolved in water for 6-12 hours. Cuttings are then bundled in groups of
25. Bundles are wrapped in perforated transparent plastic sheeting. The
wrapped packages are placed into crates which are piled to allow air
circulation. The crates are left in cold storage at a temperature above
freezing (33-35F) for the Winter. Ethylene generation is checked regularly
as it could be toxic to the cuttings. During cold storage a callus ferrule
forms around the lower end of the basal end. In the Spring the cuttings are
planted in the open.