They produce fruits in clusters, from both stems and laterals, much like a currant. And you want to prune in the same manner as a currant or gooseberry.

Keep the deer away - that's the best way to maximize yields :-)

I'm lucky in that the deer aren't even present in my area!

So, to prune like a currant / gooseberry would mean to remove wood that's 3+ years old?

I'm considering cordon-training them (2 or 3 cordons per plant) - would I be able to keep the cordons and simply prune out the laterals each year for a respectable harvest, and maybe cut down 1 cordon (of the 4-6) per year to allow a new one to grow and be trained?

They are pretty shrubby - never seen them trained as a cordon but it is possible as indicated on the attached link. And if trained as a cordon, the pruning suggestions are somewhat different - check here.

Thank you! Have you grown them? Did you like them?

I haven't gown them personally but have them growing in clients' yards. I much prefer black currants but that's a subjective analysis :-)

I had three Josataberries once. I took them out because the yield and flavour were not worth the space. They were very large and less productive than my black currants, redcurrants and gooseberries. I could get 6 currants in the same space and they are shorter too. If you have plenty of space they might be interesting to have just for variety.

That's a shame. I hope that mine are at least moderately productive. I'll give them a few years to produce trained as cordons and if that doesn't work out I'll add a second variety for cross-pollination to see if that improves things. It's hard not to give in to the temptation to add that additional variety right now though! If after all those experiments they still aren't producing, then I know that currants or blueberries produce just fine here in the Pacific NW!

Good luck with your Jostas. Since you have a new cultivar they may well be more productive than the ones I had which were cuttings from a plant growing in Germany in the 80s. I'd be interested to know how cordons work out for you. The method works well with red currants but is not commonly used with black currants and the latter are most similar to Jostas. This is because for cordons you grow a permanent framework. With black currants you cut out old wood regularly.

"Blackcurrants cordons

The blackcurrant is seldom grown as a cordon because the pruning and growing method is different to other currants and gooseberries. As can be imagined, a bush that needs its old stems removing regularly to keep it invigorated and encourage a fresh supply of fruiting wood, isn’t really going to be much use as a cordon. But if you really are tucked for space and you want to allocate just 18” for a cordon then it is still possible to grow a blackcurrant in this way, allowing the main stems to fruit for 2/3 years and then removing one of two main stems and allowing another to replace it. Not the most satisfactory of growing method but doable if you have no other choice." Source