How to Trim a Hedge

  • 01 of 10

    Trimming Hedges Evenly

    Formal landscapes often have boxwood hedges (image). Geometry plays a part in the design.
    David Beaulieu

    Pruning individual specimen shrubs in the landscape is normally not too difficult. A hand pruning sheers can be used to cut away individual branches, or a larger hedge trimmer—either hand-operated or an electric or battery-powered trimmer—can be used if your aim is shaping the shrub in a more aggressive fashion. The trickiest part is timing the pruning correctly, especially if the shrubs are flowering. Some shrubs flower on "old wood," and for these, it is important to prune them just after their annual flowering is done. On shrubs that flower on "new wood," pruning in the early spring is usually advised.

    It becomes more complicated, though, if you are trimming a row of identical shrubs that form a formal hedge. Here, it is critical that each shrub be trimmed in the same way and that uniform lines be maintained along the entire row of shrubs.

    And hedge trimming has a different goal than that for individual specimen shrubs. Since hedges are usually intended to provide privacy, it is important that the shrubs be as full as possible from top to bottom. This requires a trimming strategy in which the sides of the hedge is pruned at an outward-flaring angle, so that the top of the hedgerow is narrower than the bottom. This is done so that the lower branches along the sides of the shrubs aren't shaded by the upper branches—so they receive enough sunlight to grow and fill in the body of the hedge. When you look at a well-groomed hedge row from the end, you will notice that the top is flat and that the sides flare out slightly so that the bottom is noticeably wider. This allows the entire side of the hedge shrubs to receive adequate sunlight.

    Trimming Techniques for Newly Planted Hedge Shrubs

    The methods used for trimming a hedge will evolve over time. Newly planted shrubs require a different strategy than the same hedge a year or two later, when the shrubs are reaching a more mature stage. 

    After planting a hedge with boxwood or another shrub species, pinch back all new growth during the first year, which will induce low branching. At this stage, it is not important to create perfectly flat sides by using stakes and string as a guide. In this first year, just "eyeball" the trimming pattern as you pinch back all new growth. The tool of choice here is a pair of hand pruners, or even your fingertips. As you cut back the new growth, it will stimulate new growth and a fuller shape to the shrubs. 

    Even at this stage, though, take some pains to begin trimming back the upper branches a bit shorter than the lower branches. This will allow sufficient sunlight to reach the bottom branches. You are taking the first step to the ultimate hedge shape of an inverted vase or flat-topped pyramid. 

    This early style of pruning can be kept up for one to two years, depending on the shrub species. At the point where your hedgerow is full-bodied and beginning to assume the inverted vase shape, you can proceed to precise trimming to create a classic hedge with flat top and sides. 

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  • 02 of 10

    Tools and Materials for Trimming a Mature Hedge

    Use stakes and string to get straight lines when trimming hedges.
    Use stakes and string to get straight lines for hedge trimming. David Beaulieu

    Trimming a mature hedge requires fairly simple tools. The biggest decision you will need to make is between hand-operated hedge shears, which look like oversized scissors with long handles, and a power or battery-operated hedge shears, which bears a slight resemblance to a mini chainsaw. The choice is entirely up to you. Some homeowners prefer the relaxing peace-and-quiet offered by manual shears, while other prefer to get the work done quickly with power tools.

    To prepare for maturing a mature hedge, have these materials and tools on hand:

    • String
    • Stakes
    • Mallet or hammer
    • Scissors
    • Stepladder (for tall hedges)
    • Pruning shears
    • Hedge trimmer
    • Tape measure
    • Carpenter's level or string level (optional)
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  • 03 of 10

    The Importance of Guide Lines

    Information on pruning hedges.
    Prune off the "worst offenders" as you go, to make room for your string. David Beaulieu

    To maintain straight lines while trimming a hedge, you will need erect guide lines as a reference point. This is best done with strings attached to wooden stakes driven into the ground at the ends of the hedge row. Essentially, these string outline the shape you're striving for in trimming—they create boundaries to follow as you trim the branches. 

    This is a little more complicated than it sounds, since an untrimmed hedge is oversized, and it is difficult to run guide strings without the unruly branches getting in the way. The best way to deal with this is by using hand pruners to cut away the offending branches so that the guide strings can assume a straight line from one end of the hedge to another. You are essentially cutting channels through the shrubs so that guide strings can stretch out straight and taut and provide an accurate reference guide.

    You can usually get by with four guide strings—two on each side, one at the top and one at the bottom of each side of the hedge. On very tall hedges, though, a third interim string on each side might be helpful.

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  • 04 of 10

    Setting the Stakes and First String

    Picture showing how to use stakes and strings to get straight hedges when trimming.
    Stakes and lower string in place on one side of hedge. David Beaulieu

    The process of setting the stakes and first guide strings is fairly simple:

    1. Using the mallet, pound a stake into the ground at one end corner of the hedge. The stake location should mark the spot where you want the outside bottom face of the hedge to fall. This will be set in slightly from the reach of the longest branches. The volume of pruning you do will depend on how aggressively you want to trim, and on the shrub species. Boxwood shrubs are meant to be shaped as hedges, so they are usually trimmed fairly aggressively. 
    2. Pound in a second stake at the opposite corner of the hedge on the same side. For precision, you can measure the distance from the trunk or main stem of the nearest shrub, and make sure the distance is the same for both stakes. 
    3. Angle the stakes slightly so they "lean in" toward the top of the hedge. The amount of lean should be based on expected sun exposure, and on the height of the hedge. On the side that will face direct sun exposure, the lean of the stakes be relatively slight, but on a side that will receive more shade, the lean should be more pronounced so as to ensure the lower branches will receive as much sunlight as possible. 
    4. Attach a long string from one string to the other, near the lowest branches on the shrubs. Make sure the distance above the ground is the same from one side to the other. If the ground is level, the string should also be level; sloped ground will require a sloped string. 
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  • 05 of 10

    Setting the Upper String

    Bottom and top string both fastened on one side of the hedge.
    Bottom and top string both fastened on one side of the hedge. David Beaulieu

    Repeat the process used for the lower string to set an upper guide string marking where you want the upper edge of the hedge to fall. To ensure uniformity from end to end, measure up from the lower string to make sure the upper string is at the same distance from the ground at each end. If the ground is level, you can be very precise by using a string level to check the orientation of the string and make sure it is level. On sloped ground, its best to measure from the ground to ensure uniformity from end to end. 

    One the strings are installed, use a hand pruner to remove any branches that are deflecting the strings. The goal is to make sure the strings are straight and taut from end to end. 

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  • 06 of 10

    Install the Other Pair of Stakes and Strings

    How to trim hedges.
    Stakes and strings all in place. David Beaulieu

    The next step will be to install the stakes and strings on the opposite side of the hedge. 

    1. Repeat the process for installing stakes and strings on the other side of the hedge. Often, especially on smaller hedges, it is fine for the opposite side of the hedge to mirror the first side. But very tall hedges, or those with much different sun exposure on one side, may require a different slope profile in order to take accommodate sunlight differences. Professional landscapers will carefully consider sunlight patterns when choosing the slope of the hedge sides. For example, on a south-facing hedge (in the northern hemisphere), a pro might create a steeper slope on the north side of the hedge to take better advantage of sunlight on the side that sees more shade.  
    2. Check once more to make sure all strings are straight and taut, and, if necessary, prune away any branches that are touching or deflecting the strings. 
    3. Once all for strings are in place, use a long carpenter's level to check the slope across the top strings. Adjust, if necessary, so that the strings are level side-to-side. This will ensure that you trim your hedge so the top face is flat and level from side to side. 
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  • 07 of 10

    Trim the Top of the Hedge

    Picture showing someone shearing hedges.
    Guided by the strings, trim off the top of the hedge. David Beaulieu

    Start by trimming the top face of the hedge to create a plane that is flush with the top guide strings. Hold the hedge trimmer as level as you can as you trim. Be very careful if you are pruning a tall hedge that requires the use of a stepladder. It is best to position the ladder "into" the hedge, so you are leaning forward into the hedge as you trim. 

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  • 08 of 10

    Trim the Sides

    Information on how to prune hedges.
    This picture shows how much has to be trimmed off one side. David Beaulieu

    Trim the sides of the hedge to create planes that are as even as possible with the guide strings. The process involves removing all branches that extend past the plane formed by the guide strings. On younger hedges, the hedge trimmer alone should be sufficient to trim out the branches, but on older hedges with thicker branches, you may need to use hand pruners to cut away some branches. 

    Don't worry too much if there are indentations and thin spots in the hedge. This is normal, and the trimming itself will stimulate new growth that will fill in these areas. 

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  • 09 of 10

    Trim the Ends of the Hedge

    Picture of trimmed hedge.
    After photo: trimmed hedge. David Beaulieu

    Finally, trim the ends of the hedge.  Often, the ends are simply squared up to be vertical, but you can also angle them inward in the same fashion as was used on the sides of the hedge.

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  • 10 of 10

    Feed the Shrubs

    Fertilize your hedge after pruning.
    Fertilize your hedge after pruning. David Beaulieu

    Trimming places some stress on the hedge shrubs, and they will want to respond with new growth. To facilitate this, now is a good time to feed them according to the needs of the species. Generally, a mild feeding of compost or slow-release fertilizer is most appropriate.

    The new growth stimulated by trimming will quickly fills in any holes in your hedge. If you are insistent about the look of your hedges, you might want to repeat this trimming on a monthly basis. 

    Maintaining a precisely trimmed hedge is not always possible or practical. Some shrub species are really not suitable to serve as hedges, and some homeowners don't have the time necessary to maintain them. If, for whatever reason, you find that it is very difficult to maintain a groomed hedge, don't be afraid to consider "letting it go" to create a more informal privacy screen or "living wall." Letting shrubs assume their natural shapes can actually be more appealing in some landscapes.