Dwarf conifers are variants of conifers; they grow more slowly and remain significantly smaller than normal for the given species. For example, white pine (Pinus strobus) normally grows 80 or more feet tall, but the dwarf white pine cultivar ‘Blue Shag’ reaches only about 3 to 4 feet tall, growing slowly to form a dense, globe-shaped plant. A general rule of thumb is that true dwarf conifers reach 1/20th or less of the normal height for a species, grow less than 6 inches per year, and are still less than 6 feet tall after ten years of growth. Intermediate dwarf conifers are a bit bigger—they may reach 1/10th of the normal height for a species, grow 6 to 12 inches per year, and may be 6 to 15 feet tall after ten years.
Dwarf conifers originate in a number of ways. They may be seedlings with genetic mutations that reduce their growth, or they may arise as branch sports (mutated growth on otherwise normal plants) that are then propagated. A fascinating and fairly common origin of dwarf conifers is from witches’-brooms [pdf] —dense, twiggy eruptions of growth on branches of otherwise normal trees. Witches’-brooms may be caused by mutations, insects, or diseases. New plants propagated from a witches’-broom retain a dwarf growth habit. Most conifers are difficult to propagate from stem cuttings, so grafting is the usual propagation method for dwarf conifer cultivars.
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