Boxwood pruning

Boxwood is cut per standard restriction pruning procedure. In short, that's::

• Cut the whole plant to a size that is shorter and narrower than the goal by one year's growth.

• Also cut some of the branches back by an additional year or two. Try with these deeper cuts to remove the thickest branches, those that are older and have been cut at the same level for so long that they are basically bare wood with a twiggy top-knot.

Make this cut each year before budbreak in spring or in August after the year's growth is set. That way you can prune just once each year and also enjoy the bright spring green of the boxwood rather than cutting it off in its glory.

Same for relaxed and formal look

We follow this same pruning method whether we keep the hedge tightly geometric or allow it to assume a more relaxed version of its natural shape (Buxus x sempervirens 'Green Gem' is a mound, 'Green Mountain' is a columnar variety, etc.) The difference in the cut is in the line we draw and cut to. It's either exact or more approximate.

We might, emphasis on might, nip stray tips a month or so after the main pruning if we want a very tight shape. However, we do not and experienced gardeners with long term results in mind do not repeatedly shear new growth.

In this article we show you three boxwood hedges:

The first hedge is formal: tight and geometric. On it we show you all the steps of restriction pruning, just as we apply them to it each year.

• The second hedge is of plants kept in their natural habit (mounded variety 'Winter Gem') but are pruned to remain a foot or so shorter than they would be if left alone.

The third hedge is a rescue: It's a formal boxwood hedge that we took in hand after it had crept out of control.

Boxwood hedge, restriction pruning


Below: One November we noticed that these 5-year old boxwoods had become too big, rounded in outline and were near see-through in their middles. Looking inside the hedge, the branching told us the shrubs had been repeatedly sheared but no thinning cuts were being made. We noted our file to take over pruning the next spring.






Below, left: The next spring, looking inside the plant we see it had become very dense at the top and sides because shearing during active growth had encouraged branching there. This thicket at the outer edge blocked light from the interior, so greenery there had died. The hedge was becoming a hollow ball.
To help you see what we're doing, we'll thin first and then shear (this reverses the standard restriction pruning steps; that change in sequence is okay.)

Below, right: There, all thinned. All pieces we removed are on the ground.

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Right: In thinning we clip out about 1 of every 5 stems, reaching down to cut below the heavily branched segments. For more explanation of thinning, and to help you see what we saw in this shrub's branching, a click will enlarge this photo with explanatory graphics.




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 Above: Now as we shear we correct the bulge that was developing where there should have been a slope from base to top of hedge. (Compare before, left to after, right. You may need to notice the edge of the shrub in relation to the door in the background, to appreciate the change.)

 Below: It may seem we tax a plant too heavily by removing so much as we prune but repeated shearing takes a heavier toll by continually removing all new foliage. In 3 or 4 shearings over the course of a season as much or more foliage is removed as we took in one cut. In addition, since repeated shearing makes the plant woodier and concentrates the foliage at the outer edge, every cut removes a much greater portion of the foliage.


 Below: One year later, early spring, and we've once again made the thinning cuts. All that remains is to shear the plant to bring it down below the windowsill, as before. Despite all this cutting, it is denser and more green than when we stepped in to change the pruning routine from all-shearing.

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Boxwood hedge, informal outline, restriction pruning

Before and after the steps shown above have been taken. We prune this hedge every two years.


Boxwood hedge, rescued and being brought back in line

This is a formal boxwood hedge that we took in hand after it had crept out of control, developing "shoulders." Shoulders widen the whole hedge while shading the base so growth at the base thinned. We pruned as described above, sloping inward and also removing dead wood. There is a gap but it will fill pretty quickly from what is still lively wood in the interior.






A second boxwood hedge in the background had less lively wood because it's more shaded by trees and had also been pummeled regularly by an embedded sprinkler head. We thinned that hedge to let light reach and rejuvenate the interior wood and will put the sprinkler on a riser to stop the damage. Once the plant is stronger we'll cut it back farther.

On any plant pruned small and expected to be uniformly dense, it's important to narrow the "shoulders." Make the sides slant in to the top or they will shade the bottom and it will thin there. How much should you slant the sides? Enough that if you were a tiny person standing right at the base of the hedge, you could still see the top of the plant.