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Seasonal care for trees & shrubs: pruning evergreens

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Removal of weak, diseased, or broken branches, along with double leaders or dead evergreen branches can be done at any time with little consequence to tree health. “Conifers may be pruned any time of year, but pruning during the dormant season may minimize sap and resin flow from cut branches” (Bedker et al., 1996).

Learn more about pruning in How to Prune Trees

The following lists are of conifer diseases affecting certain conifer plants. Pruning of these plants should NOT be done during WARM, WET periods of the year (i.e. spring into summer)

Species affected by Rhizosphaera Needle Cast
Blue spruce (Picea pungens)

Species affected by Diplodia (aka. Sphaeropsis Shoot Blight & Canker)
Scots pine (Pinus sylvestris)
Red pine (Pinus resinosa)
Ponderosa pine (Pinus ponderosa)
Austrian pine (Pinus nigra)
Mugo pine (Pinus mugo)

Species affected by Cytospora Canker
Blue spruce (Picea pungens)
White pruce (Picea glauca)
Black hills spruce (Picea glauca var. densata)
Norway spruce (Picea abies)
Engelmann spruce (Picea engelmanni)

More information on each step:

Authored by Rebecca Koetter, Gary R. Johnson, and Dave Hanson: University of Minnesota
Funded in part by USDA Forest Service: Northeastern Area
Chart designed by Andrew Rose: www.handeye.us

Download & print your own poster or magnet copy of the “Seasonal Care for Trees and Shrubs in Northern U.S. Climates”

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5 Responses to “Seasonal care for trees & shrubs: pruning evergreens”

  1. David Conradi-Jones says:

    I haven’t seen any articles about wasps infesting Pinus Mugo bushes. My shrubs have infestations every summer. Will you be doing any articles on this subject?

  2. Arthur Sehlin says:

    I have 6 white pine planted as slips in 1997, now about 25 ft tall. They have never been trimmed and I want to remove the lower branches as much as 4 coming up about 5 feet. I plan to do it after the ground is frozen. Is this the right time of year and is 5 feet too much for a 25 ft tree?

    Art Sehlin

  3. Gary Johnson says:

    Art,

    To keep evergreens healthy, the most important consideration is to make sure there is enough leaf tissue that can photosynthesize. So, there’s a term called Live Crown Ratio, which is simply the ratio of the height of a tree represented by branches with leaves. For deciduous trees, the ideal is 60%. For evergreens it’s a bit different since they have most of their green leaves (needles) in the lower half of the pyramidal-shaped tree. For evergreens, then, the ideal is at least 75%.

    To your question. Seventy-five percent of a 25′ tall pine would be 18.75 feet. If you remove 5 feet of the lower crown you still have 20 feet of living crown which exceeds the minimum of roughly 19 feet. As the trees get older and taller, you can use this same rule-of-thumb to raise their crowns without declining their ability to photosynthesize normally.

    Finally, winter is generally a good time of year to prune trees. It’s usually less of an issue with the prunee than it is with the pruner, depending on how cold it is, how deep the snow is and how well-dressed the pruner is.

  4. Art Sehlin says:

    Gary,

    Thanks for the reply, I think I will just go about 4 feet this year and see how it looks this summer. This is the first I have heard about the percentages.

    Art Sehlin

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