Here is the description, you are right, in that vic is not hot enough in summer, but it seems only affecting the ripening not fruiting:
(Zizyphus jujuba) Jujubes are pretty trees with glossy green leaves that turn yellow in the autumn. Called “Chinese Date”, the fruit is very sweet, reddish brown when ripe, 1-1/2" long with a single seed. These grafted trees will grow to 20' or more but can be maintained much smaller. They are very productive and early bearing. The fruit needs hot summers to ripen well. In cooler summers pick it half brown and half green and bring it inside to finish ripening. The myth of Zizyphus is that they are all tender subtropicals, but jujubes are hardy in Zones 6-10. These partially self fertile cultivars produce better with another cultivar for pollination.
