I grow Sambucus canadensis which I believe has the same requirements as Sambucus nigra. Mine fruit on new growth and never fruit again on the same wood. So there is no advantage to leaving them alone. I prune back after fruiting or at least by winter and the bushes stay smaller and I get more fruit then I can possibly eat. The branches that bend over are usually full of fruit in my garden. I can't believe that your plants are that big and have not fruited, mine fruit when they are only a few feet off the ground. My #1 variety is 'Adams' which only stops blooming when a frost occurs.

I can usually judge how much growth to expect by looking at the current years growth. To harvest fruit I cut off the entire branch. Whatever part gets left behind will sprout side shoot that often grow long and bloom within two months.

Thanks for the info. My elderberries did fruit this year (first year after planting)but I'm just trying to figure out how to maximize fruiting for next year. I also grow a few canadensis - York and Adams. I'm surprised your 'Adams' continues to bloom all summer. My experience was taht they bloom, set fruit and then that is it.

I think its the pruning that encourages side growth which get the signal to bloom due to the season. Sometimes they grow long and bloom and sometimes they bloom while very short. They are in bloom now, which is the fourth flush of flowers for some of the bushes.

Now I just need to find a use for the juice. It taste like medicine to me. I'm gonna have to blend it with something strong just to drink it.

After the first year, prune as for Buddleja davidii. For most climates, late winter or early spring. Al