Replanting boxed Juniper
In December 2015 we received a 6' Juniper in a 16" wood box trimmed in a bonsai fashion. I think it's been in this box a very long time. It's not doing well. One small branch has lost its leaves. The others are green but no new growth from Dec. until now. We want to save this little tree and re-pot asap in a larger container, but don't know what kind of soil, amendments, etc. to use, how to trim the roots, or what special care to give it after repotting. All advice appreciated. Thank you very much! PS: photo is from early January
Thanks for your question about your juniper; I'm sorry it's not doing well! Junipers are, on the whole, easy to grow. But I don't think this juniper was destined for bonsai cultivation. Bonsai plants are severely pruned so they can be placed in containers on tables. This one is clearly beyond that.
Several conditions account for branches losing leaves/needles. Here's an article that might help identify your plant's problem(s), and another one from South Carolina. It's difficult to identify what the problem is without current pictures. Perhaps you might consider transplanting it into the soil, since, as I said, it's clearly too big to be a bonsai.