I had the chance to work with three overgrown mugo pines of varying size recently. Late in the month of May is the perfect moment for their renovation, as new growth is just beginning and can be easily edited by “candling” or pinching off the new growth. I also had to saw some branches to the base to completely eliminate them, as the tallest shrub was growing too wide for its alloted space next to a young Japanese maple and a pieris.
This plant is native to the European mountains and takes various forms that conifer enthusiasts love to collect. Mature heights can range from 10′ or less up to 75.’ At the nursery, it is certainly hard to tell how big your Mugo pine will become over time! Since this is a popular foundation plant, it’s important to get size right.
One sure clue to the eventual height is the length of the needles. Tiny needles around an inch in length indicate a true dwarf, which the American Conifer Society defines as reaching only 3′-6′ high or wide (maximum) in 10 years, growing only 3″-6″ per year. Then there is Intermediate, with mature size 6′-15′ in 10 years, growing 6″-12″ per year. Most Mugo pines in the landscape will fall into one of these two categories.
This is an adaptable shrub to extremes of soil, pH and climate as long as it is planted in full sun and well drained soil. However, Mugos are susceptible to European pine sawfly predation when under environmental stress such as extreme drought or soil compaction. Eggs begin to hatch in April and May and are well disguised among the needles until you see the heads start to move! The larvae feed on last year’s or current year’s needles. This action results in the brown clusters of needles that may be randomly spread over the shrub in the summer.
Missouri Botanical Garden’s excellent fact sheet on Pine Sawflies is linked for further information, here.