University of Maryland Extension

American Holly Shines in Extreme Cold

American holly

Author: Sara Tangren, Ph.D.
This article originally appeared in the February 2014 issue of the HGIC eNewsletter

When the snow piles up and the mercury spirals down, American holly (Ilex opaca) takes center stage in the native landscape.  The thick, green, spiny leaves, and the clustered red berries contrast beautifully with the soft, white snow.  Some people prune the lower branches from older trees to expose the handsome, smooth, gray bark.

American holly used as large-scale foundation plant at Hood College in Frederick County, Md.

American holly used as large-scale
foundation plant at Hood College
in Frederick County, Md.

American holly isn’t just good looking, though. It provides essential ecosystem functions, including providing winter shelter for songbirds.

For one thing, the dense cover offers excellent protection from the roving eyes of hungry hawks.  The American holly also offers protection from the cold.  A broad-leaved evergreen, the branches accumulate snow in a way that deciduous trees cannot, forming insulating pockets, almost like miniature igloos.  This warm, protective quality is enhanced by leaving the lower branches on the tree so that the igloo effect extends all the way down to the ground.  Juncos, white-throated sparrows, song sparrows, chickadees, titmice, and cardinals all take shelter from winter winds in the American holly’s snow-covered boughs.

To further its function as a songbird winter-storm-survival kit, American hollies also provide a critically important winter food source.  When temperatures plummet, birds generate body heat by shivering.  This calorie-intense activity comes at a time when insect food is scarce and many of the seeds birds would normally eat are hidden beneath a blanket of snow.  Even in the wintriest of weather, bright red holly berries are quite accessible, offering just what cold, hungry songbirds need: a meal rich in fat and protein.

Tips for selecting American hollies for your landscape:

  • American hollies are native to Maryland, being very abundant in most Coastal Plain forests, less common in the Piedmont, and absent from most forest communities in Western Maryland.
  • The natural range of American holly is expected to shift north and west as our climate warms.
  • Only female trees produce berries.  If you are planting next to a wild American holly population, you have the option of only planting females.  Otherwise, you’ll need to plant males as well.  Make sure the males and females bloom at the same time by choosing native plants from your region or select compatible male and female cultivars.
  • American hollies do well in moist, acidic, well-drained, sandy soils, but there are many reports of their success in dramatically different conditions.  In my own yard, with its typical suburban compact “clay” and a pH around 6.5, the American hollies are thriving.
  • American holly occurs naturally in many Maryland plant communities with different soil characteristics.  Examples include mesic, sandy, acidic soils; xeric soils; wetland soils, even tidal freshwater conditions; organic soils; high pH soils on limestone bedrock; and in soils of every texture. 
  • Yellowing of the leaves (chlorosis) will tip you off when soil pH is too high for your hollies.  If this happens, give them a little acid-rich fertilizer or flowers of sulfur.
  • They will grow in full sun or full shade.  Growth will be slowed by extreme conditions.
  • There are over 1,000 cultivars of American holly, and you’ll find many holly cultivars that aren’t American hollies at all.  Whether you are motivated by aesthetics or by wildlife support objectives, it’s hard to beat the locally native American holly.  Consider visiting your local native plant supplier.
  • Reject hollies, whether straight-species or cultivars, if their ancestry lies in areas far to the north or south of your landscape.  You want plants that can survive both the extreme winter conditions we have this month, as well as the extreme summer conditions we can expect 180 days from now.
  • American hollies can be propagated by both seed and cutting, so if you have a green thumb, consider growing your own.  They may also be rescued from farm fields, mowed areas, and development sites.

holly berries in snow

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