Pruning Hemlock Trees – How And When To Prune Hemlocks

Pruning Hemlock Trees – How And When To Prune Hemlocks

By: Heather Rhoades

Hemlock trees are a popular conifer that is commonly used as either privacy shrubs or as visual anchor trees in the landscape. Most of the time, pruning hemlocks is not necessary, but occasionally weather damage, disease or competing main trunks on upright hemlocks can create the need for pruning hemlocks. Keep reading to learn how and when to prune hemlocks.

When to Prune Hemlocks

If you find that you need to prune your hemlock tree, the best time for trimming hemlocks is in either spring or early summer. At this time, the tree is getting ready for or is already in active growth and will recover quickly from any hemlock pruning that needs to be done.

In the fall and winter, hemlocks are preparing to go dormant and are hardening themselves to be able to withstand the cold of winter. Pruning hemlock trees in fall or winter can confuse the tree, causing it to return to active growth rather than dormancy. At best, the new growth it does produce will be killed off in the cold and, at worst, the entire tree will be unable to withstand the winter cold and the entire tree will die.

How to Prune Hemlock Trees

Trimming Hemlock to Correct Damage from Weather or Disease

High winds or heavy snows can sometimes damage the branches of a hemlock and you may need to prune the tree in order to remove some of the damage or to help reshape the hemlock. Disease may also kill back some of the branches on the tree and you will need to remove the diseased branches.

The first step in pruning hemlocks is use a clean, sharp pair of pruning shears or pruning saw, depending on the size of the branches you need to prune. Clean and sharp pruning tools will help to prevent disease.

The next step in trimming hemlock branches is to select which branches need to be removed. Select the branches before you start trimming so that you do not over prune the tree accidentally.

Then make your pruning cuts just above the needle whorls. Hemlock trees will grow new branches from the needle whorls, and pruning just above them will ensure that the new branches come in properly.

If damage to the hemlock tree is extensive, severe pruning may be needed. Hemlock trees can withstand severe pruning and will recover from losing as much as 50% of its branches.

Pruning Hemlocks to Remove Competing Main Trunks

Upright hemlock varieties look best when they have only one main trunks, so home owners often want to remove secondary upright trunks that may start to grow. These secondary trunks can be pruned back to their starting point on the main trunk or can be cut at any point along the trunk to stop its upward growth and encourage side growth instead.

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How to Care for Hemlock Trees

The hemlock tree is often confused with the poisonous plant ancient peoples used to make a lethal drink. To the contrary, Native Americans once brewed a medicinal tea from the leaves and branches, according to William Carey Grimm’s "The Illustrated Book of Trees: The Comprehensive Field Guide to More Than 250 Trees of Eastern North America." In modern times, hemlock’s evergreen needles and drooping stems yield a finely textured landscape tree, often used as a specimen, screen or group planting.

Plant hemlock in partial shade or sun, preferably in moist, well-drained soil. Do not place a hemlock near a foundation, because the tree can outgrow a site if it is not pruned annually. Avoid curbside plantings as hemlock is sensitive to road salt in winter.

Amend the soil before transplanting to improve drainage. With the exception of clay soils, you can apply a 2- to 4-inch layer of peat moss or sand to the area, then till the material deep into the soil to increase porosity.

  • The hemlock tree is often confused with the poisonous plant ancient peoples used to make a lethal drink.
  • With the exception of clay soils, you can apply a 2- to 4-inch layer of peat moss or sand to the area, then till the material deep into the soil to increase porosity.

Dig a hole two to three times the size of the Hemlock root ball. Place the root ball in the hole, and then replace the soil. Avoid setting the tree deeper in the soil than it grew in the nursery. Try to maintain the original soil line.

Provide a transplanted tree with 1-inch of water weekly until established. A soaker hose allows water to trickle down to the root zone and prevent the root ball from drying out. Thereafter, water during periods of drought to reduce plant stress.

  • Dig a hole two to three times the size of the Hemlock root ball.
  • Provide a transplanted tree with 1-inch of water weekly until established.

Spread a 3-inch layer of mulch around the base of the trunk. Mulches, such as pine straw, leaves and pine bark, prevent weed competition during establishment and help the soil and roots retain moisture. A mature hemlock tree does not require mulch the low growing branches hinder weed growth.

Treat hemlock woolly adelgid infestations with insecticides. The insects feed on the needles and form cottony sacs at the base of the tree and, eventually, kill the tree. Spray the tree twice with horticultural oil or insecticidal soap to control adelgids. Injecting infected stems with insecticide in mid-May helps control adelgids for six months, according to Pennsylvania State University School of Forest Resources’ fact sheet on hemlock woolly adelgid.

  • Spread a 3-inch layer of mulch around the base of the trunk.
  • Mulches, such as pine straw, leaves and pine bark, prevent weed competition during establishment and help the soil and roots retain moisture.

Apply a balanced fertilizer to an established tree, not a transplant. The ideal mix contains nitrogen, phosphorus and potassium in 8-8-8 or 10-10-10 ratios. Fertilizer acts as a nutrient supplement, providing the tree with the minerals it needs to fend off disease, drought and pests.

Limit spring pruning to individual branches, if a natural pyramidal shape is desired. Prune branches back to the candles, or buds lower on the stem, if a dense, compact habit is preferred. Pinch off 1/2 of each candle by hand. Shears can injure needles and cause the tips to turn brown.

  • Apply a balanced fertilizer to an established tree, not a transplant.
  • Limit spring pruning to individual branches, if a natural pyramidal shape is desired.

Remove dead and diseased branches from hemlock trees.

Do not fertilize the tree during an adelgid infestation. The added nitrogen may increase reproduction.


Laura Jull, UW-Madison Horticulture, UW-Extension
Revised: 8/13/2012
Item number: XHT1013

Why prune?
Pruning is important for a variety of reasons. Pruning can help control the size of an evergreen, direct growth, or maintain plant health and appearance. Pruning can also increase the safety of an evergreen by removing broken, diseased, dead, or dying branches. In addition to pruning, selecting plants that are suited to your environment and location are very important. The ultimate height and spread, in addition to location of overhead powerlines, should be taken into account when selecting an evergreen for landscaping.

Why prune?
Pruning is important for a variety of reasons. Pruning can help control the size of an evergreen, direct growth, or maintain plant health and appearance. Pruning can also increase the safety of an evergreen by removing broken, diseased, dead, or dying branches. In addition to pruning, selecting plants that are suited to your environment and location are very important. The ultimate height and spread, in addition to location of overhead powerlines, should be taken into account when selecting an evergreen for landscaping.

How to prune specific evergreens.
Evergreen trees such as pine, spruce, fir, Douglas-fir, and hemlock require little pruning. These trees typically have a broad, pyramidal form with low branches, and should be left intact. DO NOT remove lower branches as this destroys the natural aesthetic form of the tree. NEVER remove the main, central stem. DO remove crossing, dead, diseased, or broken branches. Also remove individual branches to help maintain the tree’s natural outline. When pruning large branches, use the 3-point method of pruning (refer to University of Wisconsin Garden Facts XHT1014).

Pines: New growth in pines occurs once a year from terminal buds. To maintain a more compact, densely branched habit, remove approximately 1∕2 to 2∕3 of the elongated terminal buds (candles) before the needles expand in spring. Candles can be pinched in half (see figure), or pruned with hand pruners. Do not cut branches back to older growth farther down the stem. Pines produce buds only at the tips of the current season’s growth and will not produce new shoots farther back down the stem.

Spruce, fir, and Douglas-fir: New growth in these trees occurs once a year from terminal buds. To maintain the tree’s natural shape and promote denser growth, cut the tip of the branch back to a lateral bud. Do not leave branch stubs. In early summer, you can also remove 2∕3 of an unbranched tip to keep the tree fuller.

Hemlocks, arborvitae, and yews: These evergreen trees and shrubs have latent (dormant) buds farther back down the stem. Therefore, you can shear these evergreens in late spring or early summer after new growth has expanded. You can also prune them in spring before the new growth has expanded because any subsequent growth will hide the pruning cuts. You can also prune individual branches back to a bud or a branch to encourage more compact habit. If these evergreens are used in formal hedges, maintain the base of the hedge wider than the top to insure adequate light penetration to the bottom of the hedge.

Junipers and false cypress: These shrubs require little pruning. They have scale and awl-like foliage that can be tip pruned in summer. Selectively prune branches of these plants back to a side branch, so that pruning cuts are hidden under foliage. These plants should NOT be sheared or cut back to older, non-leafy areas because this type of pruning would take years for new growth to conceal. Do not prune these plants after August, as the new growth will not harden off sufficiently before winter.

For more information on pruning: See UW-Extension Bulletins A1817, A1771, A1730 and Extension Fact Sheets XHT1014, XHT1015, or contact your county Extension agent.

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Landscape Ideas

Call on hemlock to create a living screen on a property line or near a patio or porch. Its graceful branches will mask views in and out of your yard 12 months a year. Shade-tolerant hemlock is especially useful for planting in the shadow of taller trees. Dwarf hemlock trees make welcome additions to foundation plantings, perennial gardens, and shrub borders where they provide an upright accent and all-season interest. A favorite nesting spot for wildlife, hemlock is also a great plant for habitat-friendly backyards.


Pruning Flowering Shrubs

Heading cuts remove only part of a shoot or limb and encourage side branching and dense growth. The cut should be made just beyond a healthy bud, angled at 45 degrees and facing away from the bud. Note that new shoots will grow in the direction the bud is pointing. Susan Carlson

Young shrubs should be pruned lightly to make them grow fuller and bushier. With hand pruners, trim long, unbranched stems by cutting just above a healthy bud. This type of pruning, called heading, encourages lower side branches to develop and enhances the shrub's natural form. When selecting a bud tip to trim to, keep in mind that the new branch will grow out in the direction of the bud. Like most pruning, heading cuts should be timed to avoid disrupting the plant's flowering.

As a shrub develops, thin out old, weak, rubbing, or wayward branches where they merge with another branch. This opens up the middle of the plant to more sunlight, which keeps interior branches healthy, stimulates growth, and increases flowering.

Thinning cuts remove an entire branch where it meets another limb, the main stem, or the ground. They should be made as close to this junction as possible. These cuts help maintain the plant’s natural shape, limit its size, and open up the interior branches to light and air. Susan Carlson

Older and Neglected Shrubs

Older shrubs that have become a tangle of unproductive stems may require a more extensive program of thinning cuts, called renewal or renovation pruning, that takes at least three years. On shrubs with multiple stems that grow up from the base, like lilac, viburnum, forsythia, and dogwood, gradually remove all of the old stems while leaving the new, flower-producing growth untouched. Eventually, the new flower-producing stems will completely replace the lackluster old growth.

Neglected shrubs may call for a more drastic approach: hard pruning. Most deciduous shrubs that respond well to renewal pruning can also take hard pruning, as will a handful of broadleaf evergreens, such as privet. Using loppers and a pruning saw, cut back all stems to within an inch of the ground during the plant's winter dormancy. (For more on the correct tools to use, see Choosing and Using Pruners and Loppers) Come spring, the plants will quickly produce new shoots from the base. Of course, this technique will leave you with little to look at while waiting for the new growth.


Watch the video: Yamadori Hemlock- Collected Bonsai