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StrategiesforGrowingaHigh‐QualityRootSystem,Trunk,andCrowninaContainerNursery
Companion publication to the Guideline Specifications for Nursery Tree Quality
TableofContents
Introduction
Section1:RootsDefects......................................................................................................................................................................1LinerDevelopment.............................................................................................................................................3RootBallManagementinLargerContainers..........................................................................................6RootDistributionwithinRootBall..............................................................................................................10DepthofRootCollar...........................................................................................................................................11
Section2:TrunkTemporaryBranches.........................................................................................................................................12StraightTrunk......................................................................................................................................................13Section3:CrownCentralLeader......................................................................................................................................................14HeadingandRe‐trainingtheCentralLeader.........................................................................................17BranchDiameter................................................................................................................................................18BranchDistribution..........................................................................................................................................19Form........................................................................................................................................................................20BarkInclusion.....................................................................................................................................................21VigorandFoliarCharacteristics..................................................................................................................22Glossary................................................................................................................................................................23
Appendix..............................................................................................................................................................26
Bibliography.......................................................................................................................................................27
Foreword
ThisdocumentpresentsstrategiestoassistgrowersinproducingtreesthatconformtotheGuideline Specifications for Nursery Tree Quality(Visalia,CA:UrbanTreeFoundation).Thestrategiesarebasedonmost‐recently‐publishedandongoingresearch,combinedwiththeknowledge,skills,andknow‐howofboththepractitionerandresearcher,toproducehigh‐qualityrootsystems,trunks,andcrowns.Asresearchprogressesandnewstrategiesaredeveloped,thisdocumentwillberevisedtoincorporatestate‐of‐the‐artinformation.
Inadditiontobeingofimmediatepracticaluseforgrowers,thisdocumentshouldprovideabasisforfurtherdiscussionamongnurseryandlandscapeprofessionalsandresearchers.ManyofthestrategieshereinhavebeeninpracticeforyearsinnurseriesinCaliforniaandotherpartsofthecountry.Whilethisdocumentcontainsguidelinesbasedoncurrentandongoingresearch,moreresearchisneededtocontinuetolearnwhatmakestreesstableandhealthy.Itisouraimtoencouragesite‐andspecies‐speciZicresearchthatwillbecomethebasisformoreuniformimplementationofmethodsknowntoproducequalitytreesinacost‐effectivemanner.
Weappreciatethereviewofthisdocumentbynurseryandlandscapeprofessionalsandwelcomeyourcomments.Wewillperiodicallyupdatethedocumentasitiscirculated,reviewed,andeditedbygrowersandresearchers.Thisprocessisessentialtoourgoalofdevelopingauser‐friendlymanualthatwillassistgrowersintheefZicientproductionofhigh‐qualitytrees.
Dr.EdwardF.Gilman,Professor,UniversityofFlorida,GainesvilleBrianKempf,UrbanTreeFoundation,Visalia,CA
Copyright©2009EdGilmanandBrianKempf
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UrbanTreeFoundation115S.DollnerAve.Visalia,Ca93291
GuidingPrinciplesforGrowingQualityTreesfortheLandscape
Goodrootsystemsstartinthenurseryatpropagationinthelinerstageandrequireattentioneachtimeatreeisshiftedintoalargercontainer.LargemainmotherrootsshouldgrowstraightfromthetrunkwithoutcirclingthetrunkordeZlectingdownward.Temporarybranchesareimportanttotrunkdevelopmentbecausetheybuildastrongtrunkandrootsystem.Shadetreesgrowninthenurseryshouldhaveastrongcentralleadereveniftheleaderwillbelostatmaturity.Installationcontractorsmustprovidesimplerootandshootpruningtreatmentsatplantingtoensurethatsustainablelandscapesarecreated.
Acknowledgments
SteeringCommittee:DaveCox,LECookeNursery;HaydiBoethingDanielson,BoethingTreelandFarms;ThomasFetch,LECookeNursery;MichaelFrantz,FrantzWholesaleNursery;MarkMarriott,VillageNurseries;JohnServiss,ValleyCrestTreeCo.;SalSoriano,Monrovia:ChrisTerry,DaveWilsonNursery;RogervanKlaveren,GenerationGrowers.
Reviewers:Dr.JimClark,HortscienceInc.;Dr.LaurenceR.Costello,UniversityofCaliforniaCooperativeExtension;SamDoane,J.FrankSchmidt&SonCo.;BruceHagen,CaliforniaDepartmentofForestryandFireProtection,Retired;Dr.RichardW.Harris,ProfessorEmeritus,UniversityofCalifornia,Davis;MarkA.Halcomb,UniversityofTennesseeAreaNurserySpecialistExtension;BruceHammersmith,SkinnersNursery;GordonMann,MannMadeResources;MichaelD.Marshall,MarshallTreeFarm;JohnMelvin,CaliforniaDepartmentofForestryandFireProtection;DaveMufZly,Oaktopia.net;Dr.DanielStruve,OhioStateUniversity;DennisSwartzell,HorticultureConsultants,Inc.;Dr.GaryWatson,MortonArboretum;KeithWarren,J.FrankSchmidt&SonCo.
This document was funded in part by a grant from the California Department of Forestry and Fire Protection.
Section 1: Roots
Rootdefectsthatdevelopduringnurseryproductioncanleadtopoorvigor(Fig.1)andtreefailure(Figs.2bandc)inthelandscape.However,mostdefects,suchascirclingrootsintherootballinterior,canbemostlyeliminatedwithappropriateandtimelymanagementinthenursery.Strategiesinthenurseryshouldfocusonproducingtreesthathavestraightmainmotherrootsgrowingtotheedgeofthecontainer.Installationcontractorsshouldcorrectminorrootdefectsnearthetrunkatplanting,aswellasrootdefectsontheperipheryoftherootball.
Straightrootsgrowingfromthetrunkformastrong,widerootplate(Fig.2a).Treeswithawiderootplatearestableandrequirealargeforcetotipthemover.TreeswithdeZlected,kinked,orbentrootscandevelopasmallerrootplateandrepresentlesserquality.WhenmainwoodyrootsaredeZlectedandnotstraight,theremaybenorootplateandthetreecanbecomeunstable(Figs.2band2c).Atree’sinstabilitycanresultfromthecurvedorbentshapeofthemainrootscombinedwithincreasingcrownsize.Growingtreeswithoutrootmanagementwhenshiftingtoalargercontainersizeoftenresultsinbentanddeformedroots.Sometreesareabletoremainstabledespiterootdeformities,buttheymaylosevigorifcirclingrootsmeetthetrunkandconstrictsapZlow(Fig.1).Areducedgrowthrateoftenprecedestheothersignsofreducedvigorsuchaschloroticfoliageanddieback.
Figure2a.Straightrootsgrowingfromthetrunkformamoreorlesscircularrootplate.TreeswithstraightrootsaremorestablethanthosewithdeZlectedroots.
Figure 2b. Tree failure resulted from circling roots in the nursery container and being planted too deeply. As the circling roots and the trunk grew in diameter, they eventually rested against each other. As a result the trunk was thinner below the soil than it was above. The root growing against the trunk caused this growth constriction (see entire tree, Fig. 2c). Removing root defects during production and at planting can prevent this.
Figure2c.Increasingcrownweightonadefectiverootsystemcausedthistreetofallinawindstorm.
Figure1.Poorvigoranddiebackcausedbystem‐girdlingroots.Treesinthisconditionwillnotreachmaturityinthelandscape.
Section 1: RootsDefects
Section 1: Roots
Likethecrown,qualityrootsystemsresultfromappropriateactivemanagement.Rootballsareoftenshiftedthroughtheproductionprocesswithlittleornocorrectioninrootsystemdefects(Figs.3aandb).
Plantingtoodeeplycanalsocausedefectsattherootcollarintreessuchasmaplesandelms.DefectsonZinishedtreesmaybecorrectableifwoodyrootshavenotbecometoolargeorabundant(Fig.3b).Whendefectsarehiddenandinaccessibleorinvolvelargeroots,correctivemeasurescanbedifZicultorimpracticaltoimplement.Whenrootshavebeenleftuntreatedfortoolong,correctivemeasurescanbetime‐consuming.Theabilitytocorrectoldandseveredefectsdependsontheseverityofdefects,speciesoftree,watermanagementpractices,sizeofrootsthatrequirecutting,andtimeofyear.ItiseasiertoremovetheserootswhentheplantisyoungerthanthetreepicturedinFigure3b.Ideally,rootsshouldbeinspectedanddefectiverootsmanagedateachshifttoalargercontainer,reducingtheneedtopruneheavyrootslater.Itisoftennecessarytoremovesubstratefromthetopoftherootballtoinspectforrootdefects(seeFig.3b).Providedthatthemainrootsarerelativelystraight(seeFig.2a),treequalityandstabilitycanbeimprovedbyremovingkinked,circling,andstem‐girdlingrootsfromthetopoftheball.Rootdefectsshouldberemovedatthepointjustbehindthebendintheroot(Fig.4).Theretainedrootsegmentshouldberelativelystraightandshouldgrowradiallyfromthetrunk.Newrootstypicallygrowfromjustbehindthecutinaradialorfanlikepatternawayfromthetrunk(seeFig.11b).Somenewrootsgrowdown,up,oroccasionallykinkbacktowardthetrunk.Theseshouldbecorrectedatthenextshift.
TopView
SideViewFigure 3a. Root defects are present at each container size: liner, #5 and #15 (Harris et al. 1999).
Figure3b.Substrate(3in.)wasremovedtoexposethetoprootsinsidethecontainer.Amoderateamountofstem‐girdlingrootsgrowingovertherootcollariscorrectable.However,itisinefZicienttoallowdefectstodeveloptothisextent.Itisbesttopreventthisbypruningrootsatearlierstagesandplantingatthecorrectdepth.
Figure 4. Cut defective roots back to the point just behind the bend (A). The retained root segment is straight. Cutting them at a point after the bend (B) is not recommended because the defect remains.
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Section 1: Roots
LinerManagement
Objective:Therootcollarandinsideportionofthelinerrootballshouldbefreeofrootdefects,includingcirclingorkinkedrootsandrootsgrowingupordownthesideofthecontainer(Fig.5).Problem:Inthelinerstage,atree’srootsystemcandevelopinamatterofweeksoncegrowthbegins.Somespeciesdeveloponlyoneortwolargemainroots;othershaveamoreZibrousrootsystem.Often,rootsgrowtotheedgeorbottomofthecontainer,thenbranchordeZlectdown,up,andaroundtheperipheryoftherootball,formingatypeofshell.Withoutmanagement,someofthesesmallrootscaneventuallybecomelargeandwoody,retaintheirdeformedshape,anddevelopintoadefect(Fig.5).Rootdefectsneartherootcollarcanreducethegrowth,vigor,andstabilityofthetree.Thelinerrootballshouldnotbevisiblewhenthetrunkofalargertreeisrockedinthecontainerorplantedintheground.Leftuntreated,rootdefectsthatdevelopatthelinerstagecanbethemostdifZiculttoaddresslaterinproduction.
Practice:Treesandshrubsshouldbeplantedinlinertraysandinothersystemsthatminimizerootdefectsandencouragebranchingoftherootsysteminsidetherootball(Fig.6).AirpruningisespeciallyefZicientatcausingataproottoformbranchroots.Linersshouldbeshiftedtolargercontainersbeforenon‐correctablerootdefectsform.Table1givesseveralmethodsofeliminatingrootdefectswhenlinersareshiftedtolargercontainers.Someofthesemethodsmayworkbetterthanothersforcertainspecies,containertypes,substratetypes,linerstage,timeofyear,andtreeage.
Figure5.Circlingandkinkedrootsoriginatinginalinerpot(left).Circlinganddivingrootsinanopen‐bottomlinerpot(right).Bothtreesshouldbethrownoutbecausedefectsaretooseveretocorrect.ThetreeinFig.7acandevelopthesedefectsunlessprunedandmanagedbeforeshifting.
Figure6.Traditionalpropagationpotsencouragerootstogrowaroundthepotoralongthesidestowardthebottom.Somerootsthengrowbacktowardthesurface(right).Potsthatair‐pruneonbottomandsidesencouragebranchingofthetaprootonseedlingsandcuttings(top),formingsmaller‐diameterbottomrootsandamplelateralsnearthesurface.
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Section 1: Roots
Shaving, pruning, or “peeling off” the shell of roots on the periphery and bottom of the root ball cuts away most defects (Fig. 7). Adequate roots remain inside the root ball in most cases (Figs. 7e and 8). Some liners may be killed by this treatment but it is necessary to remove inferior plants from the inventory and prevent them from failing later in the landscape. Slicing root balls from top to bottom removes some defects but can retain roots oriented downward. Slicing can also leave intact bent root segments that generate new roots, which can grow close to the trunk. Air pruning can be a useful method to reduce root defects. Teasing or pulling roots apart and laying them straight in the substrate of the larger container can also reduce defects if done before roots become too stiff. These and other techniques are designed to encourage roots to grow radially from the trunk (Fig. 2a). Water management is critical after root pruning to avoid severe wilting and stress. Trees should be irrigated to maintain the water requirements appropriate for the species and weather. In warmer and drier weather, the irrigation frequency and volume may need to be adjusted to accommodate the reduced and disturbed root system. Some growers strip leaves from certain trees to enhance survival.
Table1.Methodsofreducingoreliminatingrootdefectswhenlinersareshiftedtolargercontainers.
• Growlinersinpropagationtraysdesignedtoreducedefects.
• Shiftlinersattheappropriatetime.• Scoreorslicetherootballfromtoptobottomin
severalplaces.• Shaveorpeeloffrootsontheperipheryofthe
rootball.• Teaserootsattheperipherysotheylaystraight
inthesubstrateofthelargercontainer.• Pruneoffthecornersfromtoptobottomofcube‐
shapedrootballs.• Removethebottomoftherootball.
Figure7e.Atleft,alinerrootballthatislikelytodeveloppermanentdefectsifnotpruned.Rootsforma“shell”atthesubstrate‐containerinterface.Shavingorpeelingawaytheperipheralrootscanremovedefects,resultinginarootsystemresemblingtheoneatright,alinerrootballwiththesubstrateremovedtoshowalinerrootsystemfreeofdefects.
Figure7a.Inspecttherootball.
Figure7b.Removeperipheralroots.
Figure7c.Continuerootpruning.
Figure7d.Rootpruningcomplete.
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Section 1: Roots
Goodrootsystem:Linerrootballwasshaved(Fig.7)whenshiftedintoa#1container.
Figure8b.Twomonthsaftershifting,rootsthatgrewdownandaroundthesidesofthelinerpotbecamewoodyandgrewindiameter.Thesewoodyrootsretainedtheiroriginalorientation,andmanyofthenewrootsproducedinthe#1containergrewfromthebottomofthelinerrootball.
Figure8d.Twomonthsafterrootpruningandshifting,thenewrootsgrewhorizontallyanddownward.Therootsatthetopofthecontaineroriginatedfromthetopofthelinerrootball,providinggreaterstabilityforthetree.
Figure8c.Sixmonthsaftershifting,themainwoodyrootsthathadbeenoriginallydeZlectedbythelinerpotcontinuedtogrowindiameter.Manyrootsthatgrewnearthesurfaceoftherootballoriginatednearthebottomoftheliner.The#1containerwalldeZlectedasecondsetofrootsup,down,andaround.Someoftheserootswillbecomewoodyandgrowintoasecondsetofdefects.
Figure8e.Sixmonthsafterrootpruningandshifting,themainwoodyrootswereorientedinamorenaturalform.Somemainrootsgrewhorizontally,whileothersgrewdownward.Bothhorizontalandverticalrootsareneededfortreestability.Theinnerrootballwasfreefromdefectssuchascircling,stem‐girdling,andkinkedroots.However,thisplantshouldberootprunedagainwhenitisshiftedtothenextcontainersizeorplantedintheground.
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Poorrootsystem:Linerrootballwasnotrootprunedasitwasshiftedintoa#1container.
Figure8a.FinishedlinerwithrootsdeZlecteddownandaroundthepotformingatypeofrootshell.
Section 1: Roots
RootSystemManagementonLargerContainers
Objective:Therootballperipheryshouldbefreeoflargercircling,girdling,descending,ascending,andbottom‐mattedroots.Mainrootsnearthesubstratetopsurfaceshouldgrowmoreorlessstraighttotheedgeofthecontainer.Problem:RootsgrowingontheperipheryoftherootballoftendeZlectdownandaroundthecontainerwallandcanbecomelargeandwoody(Fig.9a).Largerrootsattheperipheryof#1andlargercontainerscanresultfromarootboundliner,alinerplantedwithpoorrootbranchingordistribution,failuretoroot‐prunetheliner,adominanttaprootorlateralroot,atreeremaininginacontainerfortoolong,andotherfactors.Smallandmedium‐sizedperipheralrootsindicatebetterrootdistribution(Fig.9b).Rootdefectsoftenformontheinterioroftherootballifrootsarenotmanagedateachshift.
Practice:Shiftingbeforenon‐correctabledefectsform,rootpruning,air‐pruning,andteasingapartsmallrootsateachshifttoalargercontainercansigniZicantlyreducerootdefects.Air‐pruninghappenswhenrootsarepurposelyexposedtoairintheabsenceofhighhumidity(Fig.10).Roottipsarekilled,causingtheplanttoproducenewbranchingroots.Growingtreesinanopen‐bottomcontainerabovethegroundair‐prunesbottomrootsandcanreducethediameterofrootsgrowingtowardthebottomofthecontainer.Therootballimprovesbecauseofanincreaseinlateralrootgrowthandamorebranchedrootsystem.Lateralrootsthatareair‐prunedorchemicallyprunedoncontainersidesalsobranch.
Rootpruningcanremovesomeoralloftheouterrootsandsubstratefromthetop,sides,andbottomoftherootball(Fig.11a).Thestraightportionoftherootsontheinteriorisretained.In#3containersandlarger,roughlytheouter1inchofsubstratecontainsmanyofthedefects.Teasingaparttheoutersurfaceoftherootballcanbeeffectiveonyoungtreesofcertainspecieswhenrootsaresmallindiameter(seeFig.12).Thesestrategiesencouragenewrootstogrowradiallyawayfromthetrunk.Noneofthesetechniquesareveryeffectivefortreatingdefectsontheinterioroftherootball.Therefore,itisimperativethatrootsontheperipherybeinspectedanddefectsremovedateachshifttoalargercontainer.Alltechniquesworkbestwhenrootsaresmallindiameter.
Figure9a.Largerootsaregrowingontheperipheryoftherootball.Theseshouldberemovedbyshavingorpruningawaythebentportionoftheroots;however,cuttingrootsofthissizecouldkillsometrees,dependingontimeofyearandwatermanagement.
Figure9b.Smallrootsaregrowingontheperipheryoftherootball.Thisrootballshouldbeshavedwhenshifted.
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Section 1: Roots
ThetreesinFigures8eand9bshouldberoot‐prunedwhenshiftedtoalargercontainer.Shavingworksbestbecauseitislikelytocutrootsbacktoastraightradialrootsegmentattachedtothetrunk(Fig.4).Ashavedrootballwillbesmallerthanitwasbeforepruning(Fig.13).Theremaybeotherwaystocutbackrootssothatretainedrootsarepositionedradiallyandstraightfromthetrunk.Slicingandscoringtherootballarelesseffectivebecause90‐degreebendsinmainrootsoftenremain(Fig.4).Shavingcontinuestheprocessofdevelopingaqualityrootsystemthatbeganwhenthelinerwasappropriatelymanagedwhenshiftedintothelargercontainer.Rootballsshouldbeinspectedanddefectsremovedateachshifttoalargercontainertopreventtheformationoflarge,defectivewoodyrootsontheinterioroftheZinishedrootball.
Figure11a.Shaving,pruning,or“peeling”offtheperipheryoftherootballremovesmostoftherootdefectspresentattheperipheryandbottomoftherootball.
Figure11b.Newrootsoftengrowradiallyawayfromthetrunkinafanlikepattern.Somerootsmaygrowatarightangletothecutroot.
Figure10.Thevalleyoakrootsystemgrowninacontainerthatprunesrootswithair(top)hasmorelateralrootsgrowingfromthetrunkandfewerrootdefectsthanatreegrowninasmooth‐sidedcontainer(bottom).
Figure12.Teasingrootsawayfromtherootballperipheryencouragesrootstogrowradiallyawayfromthetrunk.
7
Section 1: Roots
Figure13a.Rootsmattedatthe#5rootballperiphery.
Figure13b.Ahandsawcanbeusedtoshaveorpeelawaymattedrootsfromtheperipheryoftherootball.
Figure13c.Mattedrootsremovedfromtheperipheryofthe#5containerpriortoshifting.Notethatremainingrootsarestraightandtherootballisslightlysmallerthanitwasbeforepruning.
Figure13d.Threemonthsafterrootpruning,newrootsgrewradiallyfromthetrunkintothe#15containersubstrate.
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Section 1: Roots
Shaving,pruning,orscoringtheperipheryoftherootballcanbedonewithahandpruner,handsaw,machete,diggingshovel,orothersharpblade(Fig.13b).Thisprocessdullssharptoolsquicklybutuniformlyremovesmattedrootsfromtheperipheryandbottomoftherootball(typicallyabout½to1inchon#1,deeperonlargercontainers;Fig.13c).Thetreeisthenreadytobeshiftedtoalargercontainerorplantedinthelandscape.Newrootswillgrowfromthecutrootendsintothesubstrateinthelargercontainerorthelandscape(Fig.13d).Theresultingrootsystemshouldhavefairlystraightrootsgrowingradiallyfromthetrunk(Fig.14bottomand15a).Withoutpruning,deZlectedrootscanbecomewoodyandretaintheirbentform(Fig.15b).Shavingorpruningawayrootsattheperipheryeachtimethetreeisshiftedshouldpreventmanyofthesebentrootsfrombecomingpermanentdefects,whilecreatingamoreZibrousrootball.
Figure15a.Washingthesubstrateawayshowsthatrootballshavingdevelopedagoodrootsystemwithstraightrootsfreeofdefectsextendingradiallyfromthetrunk.
Figure14.Thismaplewasnotroot‐prunedwhenshiftedtothis#15container;notetheabundantrootdefectsatthepositionofthe#3(top).Themaplerootballperipherywasshavedwhenshiftedtoa#15container(bottom).Notetherootdefectsatthepositionofthe#3arelargelygoneandnewrootsinthe#15aregrowingmostlyradiallyawayfromthetrunk.
Figure15b.Washingsubstratefromthetopoftherootballshowsnon‐correctablerootdefectsina#45container.Thesedefectsresultedfromfailingtoprunetherootswhenshiftingfromthe#5and#15containers.
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4
Section 1: Roots
Objective:Thetreeshouldbewell‐rootedbutnotovergrowninthesubstrate.Whenremovingthecontainer,therootballshouldremainmostlyintact.Whentippingthetreefromsidetoside,boththetrunkandrootballshouldmoveasone.Rootdistributionshouldbeuniformthroughoutthecontainersubstrate.Problem:Ifatreeispoorlyrootedorrootsarepoorlydistributed,alargeamountofsubstratecanfallawayfromtherootswhenshifting.Circlingandlargedescendingrootsattherootballperipherythatarenotcutduringtheshiftingprocessmaynotextendradiallyoranchorintothenewsubstrate.Thiscancreateapointofweakness.Whenthetrunkisliftedorrocked(Fig.16,right)thepoorlyrootedsmallerrootballcanpartiallyseparatefromthesubstrateofthelargercontainer’srootball.
Practice:Plantingalinerwithabalanced,branchedrootsystemcontainingampleroottips,andshiftingthetreeattheappropriatetime,combinedwithmechanicalandairrootpruning,helpsensuregoodrootdistributionandaqualityplantwithalonglifeexpectancy(Fig.17).Thesetechniqueshelppreventpoorconnectionsbetweensmallerrootballsandsubstrateinthelargercontainerandoftenencouragemorerootstogrowintothetophalfoftherootball.Figure13dshowshowshavingtheperipheryoftherootballofthesamespeciesshowninFigure16yieldsbetterrootdistributionthroughouttherootball.
Figure17.Rootsshouldbeevenlydistributedinsidetherootball(top).Whenthecontainerisremoved,therootballshouldremainintact(left).
Figure16.This#5rootballisnotwellsecuredtothe#15substratebecauserootsaregrowingfromdeZlectedrootsprimarilyfromthebottomofthe#5rootball(left).Pullinguponthetrunk(right)causesthesmallerrootballtopartiallyseparatefromthesubstrate.
Root Distribution within the Root Ball
10
Section 1: Roots
Objective:Therootcollar(theuppermostmainhorizontalmotherroots)ontheZinishedtreeshouldbewithinthetop1to2inches,andnolargerootsshouldcrossoverthemainroots.
Problem:Treesplantedtoodeeplycandevelopsevererootdefectsattherootcollar.Eventreesofcertainspecies(e.g.,maples)plantedattheproperdepthcandeveloprootdefects.Whenshiftedtoalargercontainerthesedefectsaremoreeasilycorrectedontreesmaintainedattheoriginalpropagationlevelthanontreesplantedtoodeeply.Defectsfromdeepplantingincludecircling,stemgirdling,andkinkedrootsgrowingovertherootcollaroraroundthetrunk(Fig.18a).
Practice:Treesshouldbepositionedasclosetothepropagationlevelaspossibleunlessmainrootsoriginatedeeperthan1inchbelowthesubstratesurface.Ifthelinerisplantedtooshallowly,somesurfacerootscoulddryoutandslightlyimpedetreegrowth.Ifplantedtoodeeply,stem‐girdlingrootsandotherrootdefectsmayform.Whenshiftingorplantingintothelandscape(Fig.19b),substrateandrootdefectsshouldberemovedfromthetopoftherootballontreesplantedtoodeeply.Substratecanberemoveddowntotherootcollarusingwaterorairorbyhand.Defectiverootscanbecutbacktoapointwheretheretainedrootsegmentsareorientedradiallyfromthetrunk(Fig.18).
Figure 19a. The point where the uppermost root grows from the trunk should be positioned close to the substrate surface at each shift.
Figure 18a. A circling root growing over the root collar.
Figure 18b. After removing circling roots, the remaining root segment should be oriented radially from the trunk and straight (Fig. 19a and b).
Figure 19b. Main roots at the top of the root ball should be oriented radially and straight away from the trunk.
Depth of Root Collar
11
Section 2: Trunk
Objective:Developadequatetrunkcalipersothetreecanstandonitsownwithoutanurserystake.
Problem:Earlyremovaloflateralbranchesfromthelowertrunk(4to5feethigh)onyoungtreesslowstrunkcalipergrowth(Fig.20).Thecombinationofstakingfromayoungageandearlyremovaloftemporarybranchesoftencreatesatrunkwithlittleornotaperandatreethatcannotstandonitsown(Fig.21).Thesepracticesleadtoover‐stakinginthelandscapeandtrunkbreakageatthestaketie.TreeswithnotaperaredifZiculttotransportandmanageinthenurseryandinthelandscape.Roots,trunk,andcrowngrowsloweriftemporarybranchesareremovedtooearlyintheproductionprocess.
Practice:Keepingtemporarylateralbranchesalongthetrunkofyoungtreesallowstreestogrowfaster(Fig.22).Thelengthoftemporarybrancheswillvaryaccordingtoyourobjectives.Longertemporarybranchesresultinmorecaliper.Insomecircumstances,itmaybedesirabletoheadtemporarybranchesinordertopushmoregrowthintothecentralleader.However,earlyremovaloftemporarybranchescanresultinatallandlankytree.Headedtemporarybranchesontreessoldtoothernurseriesaslinerstockshouldnotbeconsidereddowngradingfactors.Thelargest‐diametertemporarybranchesshouldberemovedateachpruninginordertokeeptrunkwoundssmall.Temporarybranchesdonothavetoberemovedwhentreesaresoldtoanothernurseryforshiftingstock,thoughitisimportanttocommunicatethistoyourcustomerssotheyknowwhattheywillbereceivingfromyou.Temporarybranchesshouldtypicallyberemoved6to12monthsbeforesaletotheenduser.Temporarybranchesaremostimportantforencouragingcalipergrowthinyoungtrees(#15containerandsmaller,Fig.23left).Theycanberemovedfromoldertrees(Fig.23,right).
Figure22.Leavingtemporarybranchesalongthelowertrunkincreasesgrowthoftheentiretree(left).Thelowertrunkwillbecomethickerandrootswillbestronger,allowingthetreetoholditselferect.Removingtemporarybranchestoosoonweakensthetrunkandslowsgrowth(right).Inmostcircumstances,nomorethan40%ofthelowertrunkshouldbeclearedoftemporarybranches.
Figure20.Goodtaperandcaliperdevelopedbecauseofthemanytemporarybranchesalongthetrunk(left).Removingtemporarybranchestoosoonresultsinpoortrunktaper,aweaktree,andlesstotalgrowth(right).
Figure21.Treesinthenurseryarestakedtoformastraighttrunk.Thispresentsaproblemonlywhenlowlateralbranchesareremovedtoosoonfromthetrunk(left).Whentrunksareaboutthesamediameteratthebaseastheyarejustbelowthecrown,theylacktrunktaper.Thisresultsinaweaktreeunabletoholditselfup(right).
Section2:TrunkTemporaryBranches
12
Section 2: Trunk
Problem:Themarketdesiresastraighttrunkthatextendsupintothecentralleaderwithfewblemishes.Openorclosedpruningwoundsorexistingheadedtemporarybranchesshouldnotbeconsideredblemishesbecausepruningwoundseventuallyclosewithnewwood.
Practice:Notalltreesrequirestaking;however,manyspeciesneedastaketodevelopastraighttrunk(Fig.23).Bamboostakesareapopularchoice,butmanyothermaterialscanbeusedincludingplastic,Ziberglass,andmetal.Thetrunkshouldbesecuredtothestakesnuglytopreventrubbing,butnotsotightthatthetrunkisgirdled.StakesshouldbesmallindiametertopreventbranchdeZlection.LargesquarewoodstakesdeZlectbranches,oftenleadingtoamisshapenoraZlat‐sidedcrown.Thetreecanbestakedfarupintothecrownwithavarietyofmaterials(Fig.24).Thereisnoneedforthestaketobeattachedtothegroundoncethetreecanstandonitsown.
Objective:As the trunk extends up into the central leader (excluding clump forms), it should be mostly straight and vertical without exaggerated sweeps or sharp bends (Fig. 23). Trunks should also be free of large wounds.
Figure23.Lowtemporarybranchesaremostimportantonyoungtrees(left).Lowtemporarybranchesarelessimportantonoldertrees;however,theycanberetaineddependingonthespecies(right).Theycanberemovedpriortosaletotheenduser.
Figure24.Stakedtreesdevelopamplecaliperwhenlowtemporarybranchesaremanagedproperly.Temporarybranchesshouldbecutbackandremovedoveraperiodoftime.Thesebranchesaremostimportantintheearlierstagesofproduction.Stakescanbepulledupthetreetohelpdevelopastraightleadertothetopofthecrown.Branchesandthemainleaderonthetreeinthesequenceabovewereheadedinordertodevelopastraighttrunkandleader.
13
StraightTrunk
Section 3: Crown
Objective:Shadetreesshouldhaveasingle,relativelystraightcentralleader,freeofcodominantstemsorothervigorousuprightbranchesthatwouldcompetewiththecentralleader(Fig.25).ThisdoesnotapplytoplantsthathavebeenspeciZicallytrainedinthenurseryastopiary,espalier,multi‐stem,clump,oruniqueselectionssuchascontortedorweepingcultivars.
Thedevelopmentofahigh‐qualitycrownhingesontheestablishmentofacentralleaderthatisconsiderablylargerindiameterthanallbranches.Somespecieswilldevelopacentralleaderandcrownontheirownandrequirelittleornointervention.Othersrequireregularpruning.Pruningpracticesusedinleadertrainingincludeheading,branchsubordinationpruning,andstaking.Somespeciescanbegrownwithseveralleaders,includingLagerstroemia,Photiniastandards,Albizzia,Arbutus,Chitalpa,Eriobotrya,Malus,Prunus,Salixandothers.
Leaderdominantspecies(excurrentform)
Problem:TreessuchasLondonplanetree(Platanus×acerifolia)willdevelopawell‐shapedcrownwithastrongcentralleaderwithoutmuchintervention(seetheAppendixforadditionalspecies).Treeswithastrongcentralleaderrequireonlyperiodicsubordinationofaggressivebranchestomaintainthecentralleader(Fig.26).
Practice:Reduction,orbranchsubordinationpruning,isanimportanttoolfordevelopinganattractiveandstructurallysoundcrown.Branchesthatarevigorousanduprightcanbekeptfrombecomingcodominantwithsubordinationpruning(Fig.27).Subordinationremovesenoughbranchestoslowgrowthbythedesiredamount.Codominantbranchesshouldbecutbacktolateralbranches,shoots,orbudspointedawayfromthecentralleader.Insomecasescodominantbranchesshouldberemovedaltogether,suchaswhentheyarenearlythesizeoftheleaderorwhentheyclusterclosetogether.
Section3:CrownCentralLeader
Figure25.High‐qualityshadetreeshaveonecentralleader(left).Poor‐qualityshadetreeshavetwoormoreleaders(right).
Figure26.Excurrent(leader‐dominant)treessometimesdevelopgoodstructurewithlimitedintervention.
Figure27.Subordinationpruningreducesthelengthofcodominantbranches(dottedlines)backtoalateralbranchpointedawayfromthetrunk.Thegrowthslowingeffectisproportionaltotheamountremoved.
14
Section 3: Crown
Figure28a.Codominantbranchestypicallygrowasfast,orfaster,thanthecentralleader.
Branchdominanttrees(decurrentform)
Problem:Treessuchaselm(Ulmusspp.),zelkova(Zelkovaserrata),andcamphor(Cinnamomumcamphora)arebranch‐dominant(seetheAppendixforadditionalspecies).Specieswiththisformtypicallydevelopcodominantbranchesthatgrowasfast,orfaster,thanthecentralleader.Thesetreeswillgrowintoaroundorvase‐shapedformataveryearlyage.Thisgrowthhabitrequiresregularpruningtoshortenbranchesanddevelopanattractiveandstructurallysoundcrown.Whentreesofthisformarenottrainedproperlyinthenursery,theycandevelopstructuraldefectsastheycontinuetogrowinthelandscape.
Practice:Branchmanagementshouldbeginearlyintheproductionprocessandcontinueuntilthetreeissold.Regularbranchsubordinationandbranchremovalensuresthatcompetingbranchesgrowmoreslowlythanthecentralleaderanddonotbecomecodominant(Figs.28aand28b).
Branchesinthecrownshouldbelessthanhalfthediameterofthecentralleadermeasured1inchabovetheattachment.Branchtipsshouldbebelowthetipofthecentralleader(Fig.28b).Branchesthatarevigorousmayrequiresubstantialsubordinationtoslowtheirgrowth(Fig.29).Branchesshouldbecutbacktoshootsorbudspointedawayfromthecentralleader.Branchesmayneedtobeshortenedrepeatedlyintheproductionprocess.Inmostcases,codominantbranchesshouldberemovedaltogether,especiallyifupright.
Figure28b.Threecodominantbranchesweresubordinated(reduced)by60to70%toslowtheirgrowthandencouragethecentralleadertodevelop.
Figure29a.Codominantbranchesaretypicallyvigorousanduprightbeforepruning.
Figure29b.Alightsubordinationpruningshowingremovalof30to40%offoliage.
Figure29c.Aheavysubordinationpruningshowingremovalof60to70%offoliage.
15
Section 3: Crown
TreesthatdonotbranchProblem:TreessuchasChinesepistache(Pistaciachinensis),jacaranda(Jacarandamimosifolia)andhoneylocust(Gleditsiatriacanthos)oftendonotbranchontheirownatayoungage(Fig.30;seetheAppendixforadditionalspecies).Treeswithoutbranchesdonotfarewellinthemarketplace.Thepracticeofheadingstemstopromotebranchingwithoutretrainingacentralleadercancreatecodominantbranchesclusteredclosetogether(Fig.31).Thisclusteringisconsideredastructuraldefectbecauseitbecomesaweakpointinthetreeasitgrows(Fig.32).Thestructuralweakpointislargelyduetothelackoffollow‐uppruningandstakinginthenursery.
Practice:Thecentralleadercanbeheadedtopromotebranching;however,thetreeshouldbetrainedwithanewcentralleader(Fig.33).Onemethodoftraininganewcentralleaderusesabamboostaketiedinseveralplacestothetrunk.Thestakeshouldextendwellbeyondtheheadingcut.Afterheadingthecentralleader,severalnewshootsshouldgrowfrombelowthepointwherethecentralleaderwasheaded(Fig.33).Themostvigorousuprightshootshouldbeselectedandpulledtightagainstthestake.Thisshootwillbecomethenewcentralleader(Fig.34).Theheadingcutshouldnotexceedabout¾inchindiameter.
Shootsotherthantheonechosenforthenewcentralleadershouldbeheadedtopreventthemfrombecomingcodominant.Theseshootsshouldbeheadedbacktoabudorientedawayfromthecentralleader.Thispracticecanberepeatedthroughouttheproductionprocesstodevelopafull‐branchedcrown.
Figure30.Somespeciesdonotbranchwhentheyareyoung(seetheAppendixforalist).
Figure31.Headingthecentralleaderencouragesbranching(leftandcenter; from Harris et al. 1999).Poorbranchstructureresultswithoutfollow‐uppruning(right).
Figure32.Thesetreesprobablyfailedbecausetheywereheadedinthenurserywithoutfollow‐uppruning.
16
Section 3: Crown
HeadingandRetrainingtheCentralLeader
Figure33.Headingtheleaderpromotesbranching(lefttoright).Thetopshootistiedtoastakeandtheothersareheadedtopromotebranching.Thisprocesscontinuesthroughouttheproductionprocess(seeFig.34forstakingdetail).
Figure34d.Thepruningwoundisclosedandthetreenowhasanewcentralleaderwithtwobranches.Thetwobrancheswereheaded(notshowninillustration)toslowtheirgrowthandtocreatemorebranches.
Figure34c.Thenewleaderisgrowinglarger.Thepruningwoundisalmostclosed.Thewoodinthenewcentralleaderwillhardenandremainstraight.Thestakecanberemovedoradjusted.
Figure34b.Threebudsdevelopedintoshootsjustbehindtheheadingcut.Thetopshootistiedtothestakewhiletheshootsarestillsoft.
Figure34a.Thecentralleaderisheadedatthepointwherebranchesareneeded.Astake(left)istiedtotheleadersoitextendsbeyondthecut.
17
Section 3: Crown
Figure35.ThisnearlyZinishednurserytreehasgoodbranchsizeinrelationtothetrunkandastrongcentralleader.Sincethesebranchesaresmall,theywillbeeasytoremoveasthetreegrowsinthelandscapeorisshiftedtoalargercontainer.
Objective:Thediameterofallbranchesshouldbelessthanhalfthediameterofthetrunkandthecentralleaderasmeasuredabout1inchabovethebranchunion(Fig.35).
Problem:Brancheslargerthanhalfthetrunkdiametercangrowtooaggressivelyandcompetewiththecentralleader(Fig.36,top).Branchesthataresmallerthanthetrunkarebetterattachedandtypicallydonotcompetewiththeleader.Branchesthatarelargerthanthetrunkhaveaweakerattachmenttothetrunk.
Practice:Brancheswithadiametergreaterthanhalfthetrunkdiametershouldberemovedorseverelysubordinatedtoslowtheirgrowth(Figs.28band29).
BranchDiameter
Figure36.Thebranchontherightislargeinrelationtothecentralleaderandshouldberemovedorreducedinordertoslowitsgrowth(topphoto).Branchesshouldbelessthanhalfthetrunkdiameter,notthesamediameterasthetrunk.Medium‐sizedbranches(seeZinger)canbeprunedmoderatelyinordertoslowtheirgrowth(bottom).Smallerbranchesmaynotneedpruning.
18
Section 3: Crown
Figure38.Thisisanexampleofhowaclusterofbranchescoulddevelopintocodominantstems(left).Thetalleststemtakesoverorseveralgrowtochokeouttheleader.Theclustercausesareductioninthevigoranddiameterofthecentralleaderabovethecluster.Afterselectingthecentralleader,thelargestthreebrancheswereremoved,andtheremainingtwosmallerbranchesontherightwerereducedbyhalf.Thebrancheswerecutbacktoabudpointedawayfromthecentralleader(right).
Figure37b.Atreeisweakwhenmostbranchesareclusteredtogether.NoticethesigniZicantreductionindiameterofthecentralleaderjustabovetheclusteroflargebranches.Thisindicatesthatthebranchesaregrowingmoreaggressivelythanwhatwastheleader.
Figure37a.Thistreehasastrongstructureandwell‐spacedbranchesinrelationtothetrunk.Noticethatthecentralleaderhasauniformtaper.
BranchDistribution
CentralLeader
Objective:Mainbranchesshouldbedistributedalongthecentralleader(Fig.37a)andnotclusteredatafewpoints(Fig.37b).Conifersoftengrowwithmanybranchesclosetogether;inmostcases,thisisZine.
Problem:Clusteredbranchesoftenoutgrowthecentralleader,andthisretardsgrowthofthecentralleader(Fig.37b).
Practice:Whentreeshaveclusteredbranches,theymustbeprunedinatimelymanner,otherwisetreequalityandsalabilitywillsuffer.Acombinationofbranchremovalandbranchsubordinationisrequired(Fig.38).Ideally,thelarger‐diameterbranchesshouldberemovedandthesmallerbranchescutbacktoabudorshootgrowingawayfromthecentralleader.Thispracticewillmaintainastructurallysoundandwell‐distributednurserycrown.Pruningshouldbescheduledtoavoidadverseimpactsfromenvironmentalextremesofweather.
19
Section 3: Crown
Objective:Treesshouldhaveabalancedformandnotbemisshapenbybreakage,wind,pruningpractices,pests,spacing,orotherfactors.Aconsistenttreeformisanimportantattributeforsalesandlandscapevalue.Itiseasierforbuyerstochoosefromablockoftreesthathaveconsistentnurserycrowns.
Problem:Aggressiveoroversizedbranchescancausethecrowntobecomeasymmetricalorone‐sided,whichreducesthesalabilityofthetrees.
Practice:Treeformcanbeimprovedbyreducing,removing,andheadingbranchestocreateauniformnurserycrown(Fig.39).Vigorousbranchescanbebroughtbackintoaconsistentanduniformshape.Treespreviouslyheadedortopped,orthosewithathincrownononeside,canbebalancedbyremovingandreducingbranchesontheheavyside(Fig.40).
Figure39.Thecrownislopsidedontherightsideofthephotoontheleft.Reducingthelargeuprightbranchandheadingsomesmallerbranchesresultsinamoreuniformnurserycrown(right).Ideally,branchesgrowingoutsideanimaginarypyramid(dottedlines)shouldbepruned.
CrownForm
Figure40.Beforepruning(left),thecrownislopsided.Afterpruning(center),thecentralleaderismoreprominentandthecrownisbetterbalanced.Reductioncuts(right,arrow),removalcuts,andheadingcutscanbalancethenurserycrown.
20
Section 3: Crown
BarkInclusion
Objective:Scaffoldbrancheswithbarkinclusionsinthecrownshouldberemovedorseverelyheaded.
Problem:Abranchiswellattachedtothetrunkwhenabarkridgeispresent(Fig.41a).Abarkridgeindicatesthatnormalwoodisgrowingovertheunion.Conversely,barkinclusionsinthebranchunionreducethestrengthofthebranchattachmentbecausebarkandwoodfoldinward(Fig.41b).Thismakesforaweakbranchattachment.Brancheswithinclusionstendtobevigorousanduprightwithnarrowanglesofattachment(Fig.42).Theyshadetheleader,whichcanpreventbrancheswithgoodunionsfromdevelopinghigherinthecrown.Ifnotremovedearlyinproduction,removalcanlaterleadtoadeformedcrown.
Practice:Branchesthathavebarkinclusionsshouldberemovedwhenthetreeisyoungandbeforethebranchbecomesanimportantpartofthecrown.Ifremovalwillleavethecrownone‐sided,thebranchshouldbesubordinated.Brancheswithbarkinclusionsoftenrequireregularsubordination.
Figure41a.Brancheswithbarkridgesonthetopoftheunionarewellsecuredtothetrunk.
Figure42.AunionwithabarkinclusionformsaVshape(seeFig.41b).Theunionisweakandbreaksaparteasilybecausethereisnowoodontopoftheunionconnectingbranchtotrunk.
Figure41b.Unionswithinclusionsareweakandcaneasilybreakfromthetrunk.Thecrackisthebarkinclusion.
21
Section 3: Crown
Objective:Thecurrentyear’sshootgrowthshouldbevigorous(showingvitality)asindicatedbyappropriateshootgrowth(lengthanddiameter)throughoutthecrownfortheageandsizeofthespeciesorcultivar(Fig.43).Treesshouldhavenodead,diseased,infested,cracked,broken,distorted,orotherwiseinjuredbranches.
Thesize,color,andappearanceofleavesshouldbeappropriateforthetimeofyearandstageofgrowthofthespeciesorcultivar(Fig.44).Leavesshouldnotbeundersized,misshapen,tattered,discolored(chloroticornecrotic),orotherwiseatypicalinappearance(Fig.45).
Problem:Treesthathavepoorhealthorlackvigorareoftenshiftedintolargercontainersizesandallowedtoremainintheproductionsystem.Thesepracticesarebadforgrowersandtheircustomers.Shiftingpoor‐vigortreesintothelargercontainersizesshouldbeavoidedwhenpossible.
Practice:Less‐vigoroustreesshouldbeculledandnotshiftedtolargercontainers.Itisimportanttoculltreesthatexhibitpoorhealthandpoorvigorearlyintheproductionprocesstoreducecost.Managementeffortsshouldbefocusedonvigorousplants.
Figure44.Thetreeontheleftdisplaystheappropriateleafcolor.Thetreeontherightispartiallychlorotic.
Figure45.Thistreeshowsscorchedandchloroticleaves.
VigorandFoliarCharacteristics
22
Figure43.Thetreeontheleftshowsverypoorvigorforthespecies,withonly3inchesofshootgrowth.Thetreeontherightexhibitsgoodvigorappropriateforthespecies,with16inchesofshootgrowth.
Glossaryair root pruning. Root pruning done in containers that causes root tips to be killed by exposure to dry air, resulting in several new roots branching behind the dead root tip.
apical. Of or relating to the main upright shoot of a plant.
apical dominance. Inhibition of lateral buds by the terminal bud of a shoot.
branch union. The point where two stems, or a stem and a branch, meet.
branch. A stem that is smaller than the main trunk to which it is attached.
caliper. Trunk diameter measured 6 inches from the ground; if caliper is greater than 4 inches, the caliper measurement should be taken at 12 inches from the ground.
central leader. A continuation of the main trunk located more or less in the center of the crown, beginning at the lowest main branch (scaffold) and extending to the top of the tree. Also referred to as the dominant leader.
circling roots. One or more roots whose diameter is greater than 10% of the trunk caliper circling more than one-third of the trunk.
clear trunk. The portion of the trunk below the crown lacking lateral branches, including the portion of the trunk with shortened temporary branches below the crown.
codominant. Two or more vigorous, upright branches or stems of relatively equal size that originate from a common point, usually where the leader was lost or removed.
crown. The portion of a tree beginning at the lowest main (scaffold) branch extending to the top of the tree.
cultivar. A named plant selection from which identical or nearly identical plants can be produced, usually by vegetative propagation or cloning.
descending roots. Roots that grow to the container wall and down the inside of the pot. Also known as plunging or descending roots.
decurrent species. Species with strong apical dominance and weak apical control. Buds do not elongate in the season they were initiated (strong apical dominance); but, when they do elongate, they have growth equal to the central leader (weak apical control).
excurrent species. Strong apical control but weak apical dominance. Lateral branches are capable of elongating in the year they were initiated (weak apical dominance), but their elongation is under strong apical control.
finished tree. A tree in its final container.
heading cuts. Cutting through a stem or branch just above a live bud that is typically oriented away from the central leader.
included bark. Bark embedded in the union between a branch and the trunk or between two or more stems that prevents the formation of a normal branch bark ridge.
23
kinked root. A main mother root that is sharply bent.
lateral. Branches growing from the sides of the main trunk.
leader. The dominant stem, which usually develops into the main trunk.
liner. A plant in its first or second container.
liner tray. A small container or group of containers designed to hold germinating seeds or rooted cuttings.
main roots. The largest-diameter mother roots typically growing from the trunk or main taproot that form the main structure of the root system.
media. See substrate.
minor root defects. Small-diameter roots circling or crossing the top of the root ball.
peripheral roots. Roots growing in the outer inch of the container root ball sides and bottom.
radial. Positioned around a central point or axis.
propagation depth. Depth at which tree was positioned in the first container or field soil.
photosynthate. Sugar and other carbohydrates that are produced by the foliage and stems during photosynthesis.
reduction cut. Cutting a stem or branch back to a live lateral branch that is typically oriented away from the central leader; also referred to as a subordination cut.
root defects. Circling, kinked, or stem-girdling roots resulting from growing in a container. Roots that deflect up or down once they reach the container wall are also considered defects.
removal cut. Removing a branch back to the trunk, or removing a secondary branch from a main branch.
root ball shaving. Removing the outer substrate and roots on the periphery of the root ball, typically using a sharp blade or saw.
root collar. The base of a tree where the main roots and trunk meet. Also referred to as the root flare.
root flare: See root collar.
root plate. The combination of roots and soil close to the trunk that holds the tree erect in the landscape.
scaffold branches. Large main branches that form the main structure of the crown.
24
shifting. Removing the root ball from a container and placing it in a larger container; also referred to as repotting, bumping up, or stepping up, up canning.
stem-girdling root. A circling, bent, or straight root that touches or rests on the trunk or root flare that can become a permanent root.
subordinate. See reduction cut.
substrate. The mixture of bark, peat, sand, compost, wood, and other materials used in containers to grow plants at commercial nurseries. Also referred to as media.
tap root. The primary, typically large-diameter dominant root that emerges from a seed.
teasing the root ball. Gently pulling roots on the root ball periphery away from the periphery and positioning them more-or-less straight in a radial position in the substrate of a larger container.
temporary branch. A small branch that is temporarily retained along the lower trunk of young trees.
thinning cut. See removal cut.
trunk. The main stem of a tree, beginning at the root collar and ending at the lowest main scaffold branch.
taper. The thickening of a trunk or branch toward its base.
wound. A discontinuity resulting from removal of bark and cambium. Pruning cuts that are not closed over are not considered wounds.
25
Appendix
Selected branch-dominant shade tree species AcaciaBauhineaCamphorCeltisCercisCladrastisFicusFraxinusGleditsiaKoelreuteriaLaurastinus Quercus UlmusZelkova Selected leader-dominant shade tree species AcerAlnusBrachychiton Cedrus GreviliaLiriodendron Liquidambar styracifluaMagnolia grandifloraPinusPlatanusPodocarpusSequoia SequoiadendronTaxodium distichum Selected tree species that do not branch on their own in the nursery DelonixEucalyptus GinkgoGleditsiaJacarandaKoelreuteria PistaciaPyrus
26
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