I am in Zone 6B, in the DC area. Last October, I planted some Nellie Stevens hollies (about 18 inches tall) that I ordered online. I made a rookie mistake and failed to assess for potential root bound or break up the root ball to ensure that the root system grows properly. Now, the trees seem to be surviving the winter OK overall, but some of them have grown very little or not at all, and they all have varying degrees of a few brittle and yellowish leaves - some of which have black spots. I've been watering pretty regularly (1-2 times per week.) Do you think all/some or my plants might be root bound? What should I do? Thanks!