Use Caution With Those Shears
Here are some tips for trimming plants that often get pruned incorrectly, says Jim Orband, an extension agent in York County, Va.:
Arborvitae and junipers
If you prune beyond the live green needles, green growth will never come back from that branch again. Prune regularly to maintain green growth, using heading and thinning cuts.
If you want to avoid lots of pruning, choose plants that are suitable for the spaces where they will be planted. Dwarf, semidwarf and slow-growing varieties are best for tight spaces.
Bears flowers on growth from past year. As the plant gets older, select the oldest canes and remove. Do not cut tip unless training the plant or the canes are turning inward. Prune to outside bud so plant will grow in that direction.
There are no specific pruning rules for hollies and most other broadleaf evergreens. Most tolerate severe pruning and are fast growers that fill in space quickly. Azaleas and boxwoods do NOT tolerate hard pruning because they are slow growers. Use thinning cuts on evergreens to let air and light in or they will be susceptible to scale and aphid attack.