Evergreen shrubs help keep a garden landscape colorful all year long, even during winter when deciduous plants drop their leaves and flowering perennials and annuals die back. Holly bushes (Ilex spp.) are especially attractive shrubs with shiny green leaves that cover the plants densely, along with berries that adorn female plants. The Japanese holly (Ilex crenata) is a holly variety that thrives in U.S. Department of Agriculture plant hardiness zones 6 through 8. It responds well to pruning, especially when done at the right time of year.
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The Best Timing
Japanese holly has small, spineless leaves densely covering its branches, which grow in a naturally pleasing pattern. When left unpruned, the plant can become 8 feet tall and equally wide. It responds well to pruning into a formal shape or trimming as part of a hedge, but can also be pruned to help control its size. The best time to prune a Japanese holly is in the early summer when it's just started to put out new growth. Avoid pruning the plant in fall or winter, because as an evergreen, it may be only partially dormant during cool weather. If winter pruned, it could produce new growth that might be damaged during a period of especially cold weather.
If you have a recently planted Japanese holly, thinning the plant during its first few years can help promote a densely branched plant that looks full and bushy. Thin it by choosing and removing entire branches at their origins from plant's main stems -- this stimulates the plant to put out several new branches at each cutting point. After the first two or three years, stop thinning and head back the entire plant by shortening the length of all of its smaller branches by about one-third. Several new shoots usually form at each cutting point, keeping the total plant dense and attractive.
For a Formal Look
Japanese holly does well as part of a formal hedge, with several plants sited in a row, with about 4 feet between each plant. A specimen can also be formally shaped and grown alone or as part of a grouping of holly bushes. For a formal look, lightly shear the plant at its surface, using hedge trimmers or hand shears. While shearing, also cut back any thin, stray shoots that protrude from the plant's surface. If you've thinned the plant earlier in the season, postpone shearing until new growth appears -- but don't shear the plant after mid- to late summer to avoid winter-burn of new growth.
When pruning a Japanese holly bush, disinfect your pruning blade or the blades of your hedge trimmer by wiping them thoroughly with rubbing alcohol between cuts to discourage spread of plant diseases. After pruning, keep the plant well watered to encourage new growth and add a 2- to 3-inch layer of organic mulch under the bush. Mulching helps conserve soil moisture and keeps down competition for soil nutrients from weeds.