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In a single motion pruning demonstrates both the artand science of horticulture. Perhaps that’s why so manyhomeowners get nervous and postpone or ignore thetask. Understanding how plants grow, why pruning isnecessary, and which tools to use can remove themystery surrounding this routine practice.

Reasons for PruningPruning is the selective removal of specific plant partsfor the benefit of the whole plant. Pruning is not a wayto compensate for inappropriate plant placement orlong-term neglect of a plant.

The reasons for pruning can be grouped into fourcategories: training a plant; maintaining plant health;improving the quality of flowers, fruit, and stems; andrestricting growth.

Training a PlantYoung, vigorously growing shrubs benefit from regularpruning. The goal at this stage is to establish the overallframework of the shrub and enhance its natural form soit matures into a structurally sound specimen. Shrubsplanted in suitable growing locations should requireless pruning as they mature.

Maintaining Plant HealthRemoving dead, dying, or diseased branches helpspromote plant health. Pruning diseased wood oftenrequires cutting into healthy tissue beyond the

infection. If you cut into infected tissue it may benecessary to sanitize the pruning tool with alcohol or amild bleach solution to prevent transferring the diseaseto another area of that plant, or to a different plant.Thinning out the canopy of dense shrubs to allow forlight penetration and improved air circulation also canhelp prevent disease problems from developing.

Improving the Quality of Flowers,Fruit, and StemsSelectively removing some of the flower-bearing stemscan enhance the overall size and quality of flowers andfruit. On flowering shrubs knowing where the flowersare produced (current year’s growth or last year’sgrowth) will help you determine what to prune.Pruning at the wrong time will drastically reduce orcompletely eliminate flowering for the season. Somedeciduous shrubs—such as redtwig dogwood—haveattractive stems or bark. The most vibrant color isproduced on young vigorous stems, so pruning theseshrubs hard (removing a large number of twigs to theground) produces more new growth which will havethe best color.

Restricting GrowthIf a shrub consistently needs excessive pruning inorder to keep it in bounds, consider removing it andreplacing it with a more appropriate plant. A neglectedor poorly maintained shrub will require extensivepruning to get it back in shape. Shrubs grown as anespalier or formal hedge also will require extensiveannual pruning.

PM 1958 March 2004

Pruning Ornamental Shrubs

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Principles of PruningWoody plants have adefinable growth habit.Knowing the partsof a branch willhelp you makecorrect pruningcuts. In woodyplants the largestbuds are locatedat the branch tipswith numerous,smaller, lateral budslocated along the lengthof the stem. Althoughthere are a number of budson a given stem, not allof them will developinto new shoots.

Woody plants exhibit a growth characteristic calledapical dominance. The high concentration of hormoneslocated at the shoot tips inhibits growth of lateral budsbelow the tip and reduces growth of lower shoots.Removing the shoot tip encourages lateral buds furtherdown the stem to develop with the top most remainingbud growing most vigorously. Removing material in onearea stimulates growth in another.

Pruning back to a new growing point is essential togood pruning. Generally a vegetative bud is visiblealong the stem and is a good point to cut back to.

On stems that grow upward, make a slanting cut at a45o angle. This will allow water to run off the pruningcut and expedites wound closure. In cases of moreextensive pruning, cut back to a lateral stem that is atleast half the size of the stem being removed. Also keepin mind the direction you want the new stem to growand select for a bud that faces that direction. A majorgoal of pruning is tocreate the desiredframework ofbranches.

The types of pruning cuts most often made can beclassified as ‘heading cuts’ or ‘thinning cuts’. Each typeof cut has a different effect on plant growth.

Heading cuts are characterizedby cutting a shoot orlimb back to a budor existing shoot.Heading cutspromote branch-ing and increasethe number ofnew shoots giving theplant a “filled in” appearance.

Axillary Bud

Terminal Bud

Node

Flower Bud

Latent Bud

Parts of a Branch

Pruning cuts in relationship to stem buds

45° angleGood cut. Too

angularToolow

Toohigh

OppositeGood cut.

Cut back to a lateral stem at least half the size of the stem being removed

Headingcut

2003

2002

2001

2000

1999

1998

2002

2001

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Thinning cuts involveremoving a stem or branchcompletely. This opens upthe canopy and increaseslight penetration and aircirculation. The stem orbranch is removed at oneof the following points:its point of origin on theparent stem; a lateral sidebranch; or the ‘Y’ of abranch junction. In casesof rejuvenation pruning,the branch is removed atground level. Thinningcuts can be used to reducethe overall size of the plantwithout significantlychanging its natural form.

After the pruning cuts are made the plant producescallus tissue around the wound margin that willultimately cover the wound. “Wound dressing”products are not recommended because research ontheir effectiveness has been inconclusive.

Rapid wound closure after a pruning cut is importantto the plant’s health. Pruning in early spring enhancesthe plant’s chance to recover because the quickestclosure occurs after leaf expansion in the spring andjust prior to the onset of stem elongation.

Pruning roses in late summer is not recommended. Itstimulates new growth that will not have time to hardenoff and as a result will be susceptible to winter injury.

Thinningcut

Pruning TermsApex—The tip of a shoot

Apical dominance—The influence a growingshoot tip has on buds and shoots below it. The highconcentration of hormones located at the shoot tipsinhibits growth of lateral buds below the tip andreduces growth of lower shoots. When you removethe shoot tip, lateral buds further down the stembegin to develop, and the top most remaining budwill grow most vigorously.

Bud—An undeveloped shoot, leaf or flower or acombination of leaves and flowers. Buds form onthe sides or ends of shoots and in the angle formedwhere a leaf is attached to a shoot.

Heading cut—Removingpart of a shoot or limbback to a bud.

Rejuvenation pruning—Method of renovationfor overgrown shrubs; each year for three yearsone-third of the oldest stems are cut back tothe ground. See page 6.

Renovation pruning—Drastic method of treatingovergrown shrubs by removing all stems backto about 6 inches from ground level. See page 6.

Root sucker—A shoot that arises from theroot system.

Shoot—The growth of a branch for one season.A ring of small ridges (the bud scale scars) on abranch mark the start of a season’s growth.

Thinning cut—Removingan entire shoot or limbto the point whereit originates.

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Choosing and Caring for

Pruning ToolsTo extend the lifeof pruning tools,use the righttool for a joband avoidtwisting orstraining it.Clean and oiltools regularly by wipingan oily cloth on blades and other surfaces. Keepcutting edges sharp by regularly using an oilstone.Wooden handles should be varnished or regularlytreated with linseed oil to keep them from crackingor splintering.

Hand Pruning ShearsStems up to half inch indiameter can be prunedwith hand shears. Handshears are available ineither a scissor-actionor anvil-cut type.Scissor-action shearshave a thin, sharp bladethat slides closely past athicker sharp blade. These shears make a clean,close cut. Anvil type shears have a sharp blade thatcuts against a broad, flat blade. Cuts with this typeof shear tend to be more ragged.

Lopping ShearsLopping shears aresuitable to useon stems betweenhalf inch and 2 inchesin diameter. Lopping shearshave long handles and areoperated with two hands.

Pruning Guidelines

for Specific Shrub Types

Deciduous ShrubsDeciduous shrubs make up the bulk of most landscapes.Consider the growth habit and flowering time beforepruning. Routine pruning tasks include removing dead,diseased, or damaged growth, and deadheading. In somecases a shrub may have a stem that is reverting back toits natural form (i.e. losing its variegation). These stemsshould be removed.

Pruning Decisions Based on Growth Habit

Cane-type shrubs producenumerous, long, relativelyunbranched stems andrespond well to regularthinning. The new,vigorous shootsthat develop as aresult of thinning willproduce more flowersthan the older stems.

ExamplesDeutzia species, DeutziaForsythia species, ForsythiaKolkwitzia amabilis, BeautybushPhiladelphus species, MockorangeRosa species, RoseViburnum species, Viburnum

Shrubs that have apermanent framework-type growth habitbenefit from selectiveheading cuts to enhancethe plant’s overall shape.

ExamplesRhododendron species,

Rhododendron and azaleaHamamelis species, Witch hazel

Scissor-action

Anvil-cut

Lopping shears

Cane type

Framework type

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Pruning Decisions Based on Time of Flowering

The majority of spring-floweringshrubs bloom on the previousyear’s growth and should bepruned immediately after theybloom to allow adequate timefor new growth during the summer.Flower buds for thefollowing year willdevelop on this newgrowth.

ExamplesChaenomeles japonica, Japanese quinceChionanthus virginicus, Fringe treeDeutzia species, DeutziaExochorda racemosa, PearlbushForsythia species, ForsythiaLonicera species, HoneysucklePhiladelphus species, MockorangeRosa species, Rambling roseSpiraea species, Spring-blooming spireaSyringa species, LilacViburnum species, ViburnumWeigela florida, Weigela

Shrubs that bloom in midsummer or fall do so frombuds that form on the current season’s growth. Thesespecies should be pruned in late winter or early springto promote vigorous growth early in the summer.

ExamplesHydrangea arborescens, Smooth hydrangeaHydrangea paniculata, Panicle hydrangeaPotentilla fruticosa, PotentillaRosa species, Hybrid teas, Grandiflora, FloribundaSpiraea bumalda, Bumald spireaSpiraea japonica, Japanese spirea

Shrubs that are grown predominantly for their attractivebark, fruit, or fall leaf color should be pruned in latewinter or early spring.

ExamplesCornus species, Redtwig and Yellowtwig dogwoodEuonymus alatus, Burning bush

Pole PrunerPole pruners have a hooked blade aboveand a cutting blade beneath. The bladesare on a 5- to 6-foot long pole and areoperated by pulling on a long piece ofcord. The pole can be made of variousmaterials such as plastic, fiberglass,aluminum or wood. Fiberglass andplastic poles are good choices becausethey tend to be lightweight and don’tconduct electricity.

Hedge ShearsManual andpower shearsare availablefor trimming hedges.Manual shears havelong, flatbladeswith relativelyshort handlesand are goodfor small jobs. Electric shears are a goodchoice for larger hedges.

SawsA number of pruning saws are available. Thesesaws come with either curved or straight bladesand of variable lengths and points.Curved blades that cuton the drawstroke areeasy to use.Fineness of the cutting edge is measured inpoints (teeth per inch). Most pruning saws arein 51⁄

2 to 6 points. Blades with 8 or more points

are suitable for delicate pruning on small limbs,while a 41⁄

2-point blade is good for thicker

(21⁄2- to 3-inch diameter) stems.

Bow saws are best used when the plant isheavily branched so other branchesdon’t get in the waywhen pruning.

Polepruner

Bow saw

Pruning saw

Electric hedge shears

Hedge shears

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Formal HedgesNearly all hedges require regular and careful pruningto keep them healthy and attractive but formal hedgesrequire the most maintenance. By shearing and usingcareful heading cuts hedges can be pruned into avariety of shapes.

The most important goal when pruning a hedge is toallow sunlight to reach all parts of the canopy, includingthe base of the plant. Hedges that are wider at the topthan at the base often have little foliage near the bottomdue to lack of light. A better option is a pyramid formwhich lets light reach the entirety of the hedge.

Good choices for formal hedges includeBuxus species, BoxwoodLigustrum species, PrivetRibes species, CurrantTaxus species, Yew

Overgrown ShrubsDrastic pruning can beused to rejuvenate someovergrown shrubs.Renovation involvescutting all stems backto about six inchesfrom the ground.

As the new stems developsome additional thinningand heading cuts will benecessary to shape thenew plant.

Examples of shrubs thatcan tolerate severepruning include

Berberis species, BarberryChaenomeles species, Flowering quinceCornus species, DogwoodForsythia species, ForsythiaKolkwitzia amabilis, BeautybushLigustrum species, PrivetPhiladelphus species, MockorangeRosa species, Shrub rosesSpiraea species, SpireaSyringa species, Lilac

A less drastic approachis to remove one-thirdof the stems ineach of threeconsecutiveyears. Whendoing rejuvenationpruning, start withthe oldest andtallest branches andremove them toground level. Repeatthis the followingtwo years. As new stemsdevelop they may needheading to direct the new growth.

Renovation pruning

Rejuvenation pruning

Snow accumulateson broad, flat top

Straight lines requiremore frequent trimming

Roman arch Gothic arch

Peaked and rounded top hinderssnow accumulation

Good shape—base gets sun

Poor shape—weak growth at base

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type of rose. Floribundas and hybrid teas should be cutback to 12 to 18 inches. Most grandifloras should becut back only to 24 inches.

Albas, Damask, Gallica, Moss

These once-blooming favorites bloom on the previousyear’s growth and produce a single flush of blooms inearly summer. Spring pruning should be limited toremoving dead or diseased canes.

Ramblers and Climbers

These roses tend to have a vigorous growth habitand need regular pruning and training to keep themattractive and flowering well. They do best whentrained to a trellis, fence, or other support.

Only a limited number of roses in these categories canbe successfully grown in Iowa. Some bloom on currentseason's growth (Example: 'Blaze'). Others bloom onthe previous year's growth (Example: 'William Baffin').

The severe winter weather in Iowa usually causessignificant dieback of the older canes. Dead or damagedcanes should be pruned in the spring. Start by removingall canes that are completely dead; then use selectiveheading cuts to direct the new growth of the remainingcanes. If necessary during the growing season, thevigorous new growth can be shortened and thinnedto maintain the desired plant form.

RosesAll rose bushes benefitfrom some type ofpruning to improveflowering. Pruningalso helps reducedisease problemsby improving aircirculation or byremoving existingdiseased tissue,producing a moreattractive plant.

Some roses bloom on the current season’s growth,while others bloom on the previous year’s growth.Those that bloom on current season growth tend to berepeat bloomers and will bloom almost continuouslyfrom early summer until frost. Roses that bloom on theprevious year’s growth are once-blooming types andhave a single flush of blooms in early summer.

Hybrid Tea, Grandiflora,

and Floribunda

These roses are repeat bloomersand bloom on current seasongrowth. They require annualpruning in the spring afterwinter protection is removed.A severe winter may causeextensive dieback on existingcanes. In this case, cut thecanes back to live tissuewhich is green and has plumpbuds. If there is no green tissue,the cane is dead and should beremoved completely. If thewinter has been less severe,prune canes in early spring before they leaf out, aboutwhen the forsythia blooms. Remove damaged orcrossing canes and those that are growing toward theinterior of the shrub. Select 4 or 5 healthy canes whichare well spaced around the plant and cut these back by

Remove diseased tissue

Prune annuallyin the spring

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For more informationContact your local Iowa State University Extensionoffice for additional information or copies of thefollowing publications.

Deciduous Shrubs, PM 1943 ($)Growing Rhododendrons and Azaleas in Iowa, RG 704Iowa’s Shrubs and Vines, IAN 307 ($)Pruning Shade and Flowering Trees, PM 1304Pruning Trees and Shrubs, SUL 5 ($)Roses for the Home, NCR 252 ($)

Additional information also is available from theseWeb sites:

ISU Extension publications—www.extension.iastate.edu/pubs

ISU Forestry Extension—www.ag.iastate.edu/departments/forestry/ext/ext.html

ISU Horticulture—www.yardandgarden.extension.iastate.edu

Questions also may be directed to ISU ExtensionHortline (515-294-3108), Monday–Friday, 10 a.m.–noon and 1–4:30 p.m.

If you want to learn more about horticulture throughtraining and volunteer work, ask your ISU Extensionoffice for information about the ISU Extension MasterGardener program.

Prepared by Ann Marie VanDerZanden, extensionhorticulturist, and Diane Nelson, communicationspecialist. Illustrations used by permission fromOregon State University Extension Service. Cover andtool illustrations by Jane Lenahan, graphic designer,Instructional Technology Center. Designed by ITC.

ConifersFor pruning purposes conifers are divided intotwo types.

Scale-like Foliage and a Random Branch

Arrangement

Juniperus species, JuniperThuja species, Arbovitae

Conifers in this group can be pruned the same wayas flowering shrubs. Heading cuts will encouragedense growth while thinning cuts will help maintainthe overall shape of the shrub. New branches willonly develop as a result of heading cuts if the branchremaining still has foliage on it.

Needle-like Leaves and Whorled Branches

Abies species, FirPicea species, SprucePinus species, Pine

This group of conifers can bepruned by removing all orpart of the “candle” or newgrowth. In spring when thelight-colored candle is stillsoft, pinch it with yourfingers or prune with handshears. This is a type of heading cut and will producedenser growth and maintain the overall plant size.Don’t make thinning cuts on this type of conifer as itmay create unsightly gaps in the branching pattern.

Yews (Taxus) have an abundance of buds on bothold and new wood. New stems will develop after cut.This group of shrubs can be sheared heavily withoutpermanent damage and lends itself to formal hedges.Prune just before new growth begins in the spring.

File Hort and LA 4

… and justice for allThe U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, gender,religion, age, disability, political beliefs, sexual orientation, and marital or family status. (Not all prohibited bases apply to all programs.) Many materials can bemade available in alternative formats for ADA clients. To file a complaint of discrimination, write USDA, Office of Civil Rights, Room 326-W, Whitten Building,14th and Independence Avenue, SW, Washington, DC 20250-9410 or call 202-720-5964.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914 in cooperation with the U.S. Department of Agriculture.Stanley R. Johnson, director, Cooperative Extension Service, Iowa State University of Science and Technology, Ames, Iowa.

Pinch toremovepart of

the candle