I planted 6 black lace elderberry plants last year and they grew to about 2-3' tall. However this spring none of the plants came back from the old growth. They are all coming from new shoots. 2 of them did not come back at all. It does get some shade and some sun. I would say about 50/50. 2 of the plants is at about 1.5' now and the others are at about 6". Can anyone give me some ideas to help them thrive? Should I prune the old growth that does not have anything growing back? Thanks!