Boxwood: Regulating Canopy Density

Fig. 1   Boxwood (Boxus microphylla japonica 'Green Beauty') hedge.

Boxwood is a popular hedge material because it is evergreen with a dense growth  habit.   In my garden hedges of boxwood (Boxus microphylla japonica 'Green Beauty') provide walls around the lawn and divide the yard into different garden rooms.  When other plants die back in the winter, the boxwood hedges remain as strict reminders of the discipline that I have set for my yard. 

When leaves cease to be useful
Healthy leaves of boxwood remain on the plant for two to three years.  I have observed that the leaves that were cut during trimming in the spring of last year are still green and intact (Fig. 2).  Regular trimming maintains the shape of the hedges as it also promotes more branching.  However, as the new growths spread out, the older leaves get covered and deprived of sunlight.  Leaves that do not get enough sunlight become photosynthetically inactive and dependent creating an increased deficit on food supply for the ever increasing foliage.  Eventually, the dependent leaves get less and less ration until the plant decides that they are no longer useful for the plant.  Plants in general, have a very accurate accounting process in this regard.  When a leaf if considered unproductive, the plant will separate it by blocking the passage way for food supply until the leaf is completely dead and detached.  Technically, this process is called abscission.

Fig. 2  Boxwood retains its leaves for more than two years.

When less is more
 
To maintain a healthy boxwood shrub or hedge, the ratio of the active to inactive leaves need to be increased.  As a general rule, all leaves need to get exposed to sunlight. This can be achieved by thinning the branches to allow sunlight to reach into the depths of the canopy.  Thinning also improves air circulation within the hedge thus preventing the growth of diseases. 

Tips for Thinning Boxwood
1.   Cut off branches from within.  From the dense sides of the hedge, cut into the canopy, six to eight inches long - one branch at a time.  Repeat the process throughout until the desired density is achieved.
 
2.  Make way for light and air within.  The process creates open spaces or holes for sunlight and air to penetrate the interior canopy of the plant.  With time, new branches will grow from the inner canopy making the plants healthier and less likely to be infected by fungal diseases.

3.  Change canopy density.  While thinning, keep in mind to maintain the shape of the plant.  Thinning is not intended to change the size or shape of the plant.  Instead, it is the removal of excess branches from a crowded canopy. 

4.  Thin prior to the next growth spurt.  Boxwood put on new growth in the spring and fall.  When the need for thinning arises, it is best to do it before the next growth spurt.  It is easier to spot overlapping branches before the older branches get overgrown by the new ones. 

In my garden, some parts of my hedges are in need of thinning.  One of these days, with my sharp pruners, I will have a date with my boxwood.

It takes years to grow a good hedge of boxwood.  Thinning contributes greatly in keeping them healthy and strong.

Rocks and Hedges

Fig. 1   Boxwood (Buxus microphylla)



This is the section of our yard which we call 'Down Under'.  Our yard was sloped on one corner and we were determined to use every square inch of it.  Solution - we had this rock wall built for us.  The backyard lawn, an open area for playing, is located behind the hedge.  The second problem arose when our kids started to run and jump into the 'Down Under'.  Mothers would agree with me that this is just too dangerous for tiny people - my youngest at that time was one-year old.   Therefore boxwood (Fig. 1) were planted later to prevent the kids from diving into the lower section of the yard.




Fig. 2  Moss growing on rocks.

  A decade later (Fig.2) the hedge wall continues to grow.  It requires a minimal maintenance which includes trimming twice a year and soaker-hose watering once a week during the hot summer months.  Every other year, Redwood compost is applied over a thin layer of steer manure around the base of the plants.  This process helps increase soil organic matter and earthworm population.  The fertility and water-holding capacity of the soil is improved - both important in our area with hot and dry summers. 



Fig. 3   The combination of the wall and the hedges provides strong lines in the landscape.

 Our yard started out as a rocky piece of land (approximately forty percent rocks).   Every plant that we planted in this yard (except in the vegetable garden) required a crowbar.  Sometimes we just dig out a single piece of rock and  there is a hole enough to hold a five gallon plant.  The rocks used on this wall (Fig. 2 and 3) are serpertine [1], similar to the rocks that are found in our property and the rest of the area.  In fact, some rocks that were mined from our yard during the landscaping process became part of the rock wall.

Fig. 4   'Down Under' in the fall of 2010.

The rock wall and the boxwood hedge are structures in the garden that provide a sense of permanence. When the season brings the rest of the garden into dormancy, they remain green (Fig. 4) providing the garden the needed interest.

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[1]  The Natural History and Environment of El Dorado Hills. 

Permanent structures in a garden are like the eyes, lips and nose on a face.  Design them carefully for timeless beauty in the garden.