I'm fairly new to gardening and in need of some guidance. I've searched around for a bit but couldn't find anything except general care and pruning instructions.
Two years ago, I purchased and planted three Elder (Sambucus nigra) plants. They were all bought at a professional garden centre and came at around 15 cm in height. I planted them in a box 3 m by 0.5 m with around 85 cm between each plant. Soil depth is around 40 cm. I let them grow wild (no pruning) and gently guided the canes along a bamboo fence.
All three have been growing nicely but come spring this year only the outer two have sprouted leaves in any number. The middle one has reached the highest but the few leaves actually on it are all rather dry and curled up with a yellowish colour. They have all been watered equally and all have received one round of standard fertiliser last year. I've included a picture for comparison.
Does anyone know why the middle one is not sprouting leaves? They have all received the same amount of water, fertiliser and sunlight and given how similar they have been growing up until now, I'm baffled as to what I did wrong. I planted all of them to serve as a natural fence to the common part of our rooftop terasse and hope to grow them slightly taller but none of that will matter if there are no leaves.
Any ideas as to what can be done? As I said, I don't really have any experience taking care of anything other than the odd cactus so I'm open for any suggestions that might help.