I've got some hollies around a fence that in the past have been kept at a lower height. This year I want to let them grow about a foot or so taller to the top of the fence. They have not been trimmed yet this year. Normally it seems like we cut them 2-3 x a summer but so far this year I'm not seeing a lot of growth. Do you cut them to stimulate more growth or leave them be? Here's what I'm talking about.....you can see some new growth but not a lot.