Beginner Gardening: Holly has dead branches, looks sparse- what is wrong?, 1 by breathehope

breathehope wrote:
This holly has been struggling for the past three years. I noticed that the roots are spread out, and I found out too late that the hole was dug too small.

It recently started growing new branches after I sprayed some insecticide on it. I guessed it might be infected with mites because the trunk had spots on it and the leaves had spots on it. But now I don't know whether I should cut off the dead branches because when I did that last season nothing changed.

I have a bush (don't know the name) that is next to this holly and it seems to have a similar problem. Spots on leaves and dying branches.

I don't want to spray unnecessary chemicals and would love some help.

What can I do to get it to grow fuller and healthier?