I planted a male and female holly bush last summer, with mulch. I live in Massachusetts, so it was a cold winter. The bushes are very sparse this summer. What could be the problem and what can I do?
When hollies are thin, it's a good idea to give them a shear...just a light all-over shear. This encourages the shrub to branch and thicken up. The best time to do this is in early spring before first flush of new growth. However, it is not too late to do it now. I wouldn't wait any longer. If done now, new growth will have time to harden off before cold weather. If you wait, tender, new growth can be damaged easily by an early frost. I suggest that this be done around the middle of March, that's when our 6b zone flush starts. This article has holly pruning information:https://www.gardeningknowhow.com/ornamental/shrubs/holly/trimming-holly-bushes-how-to-prune-holly-bushes.htm