Pruning a Dwarf River Birch (Betula nigra ‘Little King’)

Betula nigra, the river birch, is a very common shade tree in the Midwest.  This is especially so since the introduction in 1979 and gradual recognition of the Heritage River birch cultivar (Betula nigra ‘Cully’), which culminated in it winning the 2002 Urban Tree of the Year award as determined by responses to an annual survey in arborist magazine City Trees. This magazine serves as Journal to The Society of Municipal Arborists (SMA) and it’s readers select a new tree each year.

Betula nigra 'Little king' before pruning

Betula nigra ‘Little King’ before pruning

The three most common birch species grown in urban environments in America are paper birch, European white birch and the heat-tolerant river birch. River Birch, or Betula nigra, seems to be the only birch truly adapted to the hardships of urban conditions.  It is also the only one that is resistant if not practically immune to the bronze birch borer, a scourge of white barked birches.

Dwarf River birches for urban settings

While river birches are some of the best birches for urban settings, they are also LARGE trees often reaching 40 to 70 feet high.  This makes them a bit large for a lot of garden uses.  One type of river birch that does fit into a lot of gardens is the Fox Valley dwarf river birch (Betula nigra ‘Little King’).  This tree was discovered and introduced in late 1970’s by Jim King of Oswego, IL and in 1991 promoted through the Chicagoland Grows program.  It is a dense compact growing tree with great exfoliating bark that only grows to 10 to 12 feet after 15 years or so.

This dwarf river birch can grow into a dense shrub like form that so effectively blocks out light that the entire inside “dies out.”  That is how this one appeared before I thinned it, as exhibited by this photo.

Betula nigra 'Little King' pruning debris

Pruning debris

As you can see, in the summer you cannot even see past the outer shell of the plant to it’s attractive exfoliating bark.

Pruning the dwarf river birch

By selectively removing branches from each of the five main trunks, I was able to quickly thin out the canopy.

I then looked at the tree from different angles and looked for the areas of foliage that appeared especially dense.  I then went back to these areas and thinned some more branches out.  I then looked at the plant again and this time from the outside of the tree, selectively thinned out the clumps of whorls of branches.  This was so that instead of 6 small branches occupying an area, only 2 or 3 did.  These were much smaller branches I was cutting, perhaps only ¼” thick.

When pruning birches including dwarf river birches, it is best to avoid Spring and Fall pruning when the sap is flowing as this will stain the branches and trunks by “bleeding” sap.

Betula nigra 'Little King' being pruned

Almost done

A late August or early September pruning is probably best as the leaves have produced most of the energy for the tree that they will produce and the hottest most stressful part of summer is past.

Pruning load is the percentage of foliage that is removed from a tree during a pruning session.  Some trees can handle a larger pruning load than others.  Birches are sensitive trees.  Therefore, I limited the pruning load to 15-20% for this session.  Conventional standards recommend no more than 25% of the foliage to be removed, but at Anderson Japanese Gardens where I work, we routinely remove 50% to upwards of 70% of a tree’s foliage with no ill effects.  Keep in mind those trees have been trained every year since they have been planted and have adapted to this level of pruning.  They are also not 70 foot high shade trees. But instead have been kept for the most part under 25 feet, so they do not have the structural requirements of a large shade tree.

While this dwarf river birch was not heavily trained as would occur in a Japanese garden, by exposing more of the exfoliating bark and also opening up the canopy to allow more light to shine into the tree’s interior, I think this subtle pruning resulted in a nicer looking and healthier tree.  What do you think?

Betula nigra 'Little King'

Betula nigra ‘Little King’ after pruning

For more information on this dwarf river birch see http://www.chicagolandgrows.org/downloads/foxvalleyriverbirch.pdf

If you have some pruning in your future, you might want to take a look at my Recommended Tools page for some tools to make the job easier.

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Comments

  1. says

    Stumbled on your blog researching this river birch. Your post helped me see that this could be the right tree for my yard and seeing it pruned really helps. Thank you!

  2. Charity says

    Finally found this article after spending a couple of hours trying to figure out how to save my specimen, planted too near a chain-link fence. Now I think I can do it. Thanks a lot!

  3. Kurt Oehlberg says

    Very good article on pruning Fox River Birch. I have two to do this year. Is it acceptable to prune them late winter (before sap flows)? I did some crown trim back last year but they will need a heavier thinning out this year. I’d hate to have to wait til August-Sept. Appreciate any guidance. Many thanks.

    • says

      Kurt you will get some “bleeding” so I would minimize the size of your cuts in the winter. I would try to wait till summer for most of your pruning.

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