Hello, I purchased 2 Viburnum lentago (Nannyberry) plants at the BANPS plant sale this weekend. Both plants appear to be water sprouts, each has two shoots about 120cm long and covered in leaves. Neither plant has branches. If I prune the tops, will that encourage branches to form? Is there anything I should to to promote a natural shrub shape? Many thanks,
What a great find at the BANPS plant sale!
It is likely that those are suckers, not water sprouts. Nannyberry (Viburnum lentago) is an excellent plant but it is infamous for producing many suckers around the base. That is, in fact, how your current sapling will develop more stems, thus creating a shrub form. Just be patient. However, you many want to prune the existing stems back to about 75 cm, to encourage branching.
Of course, you can also grow Nannyberry as a tree, in which case, you would choose the sturdiest of the two stems to be the leader, which you would cut back as above, while removing the other stem.
You would then have to monitor the tree for suckering at the base. (And maybe dig those suckers up and start a Nannyberry collection!)
Here’s an excellent factsheet about your new plants from the Smithsonian Institute. Also an well-illustrated guide to pruning shrubs from Iowa State University.
Fine Gardening magazine has a very good online article on pruning Viburnums, specifically, with excellent photos. Although Fine Gardening has a paywall, you are allowed to view a few articles for free before they demand a subscription.
Good luck with your new shrubs!