In the previous issue of Conifer Corner, I introduced the ...

y Dr. Bert CreggIn the previous issue of Conifer Corner, Iintroduced the Cupressaceae or cypress family.This family consists of evergreen trees andshrubs that are characterized by having flattenedor scale-like leaves. It includes a wide variety oftrees that are important in landscape, forestry,and conservation systems. Last time I discussedmembers of the Cupressaceae that are commonlyreferred to as “cypresses” or “false cypresses”such as the genus Chamaecyparis. In this issue I’llpresent trees and shrubs that are often referredto as “cedars” or “redcedars”. This includes thegenera Thuja and Juniperus, which, botanicallyspeaking, are not true cedars (see sidebar).32 The Michigan Landscape

Thuja: One of the remnants of myforestry training is that I still referto Thuja plicata as Western redcedarand Thuja occidentalis as Northernwhite-cedar, although I’ve been aroundhorticulturists long enough that I’vebecome conditioned to using arborvitaeas a common name. Interestingly, thecommon name arborvitae (meaning “treeof life”) comes from the fact that NativeAmericans taught early French explorersto use foliage from Thuja occidentalis toprevent scurvy. By almost any measure,the number of arborvitae cultivars in thenursery trade is staggering. The AmericanConifer Society Database lists over 150cultivars of Thuja occidentalis and MichaelDirr Lists 40 cultivars of Thuja plicata.The vast number of cultivated varieties isa testament to great variability with thetwo species as well as their relative easeof propagation by rooted cuttings. In thetrade arborvitae are often distinguishedsimply by cultivar and frequently littleattention is paid to whether a cultivar isT. plicata or T. occidentalis although Dirrsuggests that T. plicata is superior from anornamental standpoint.September/October 2004Thuja plicata: In its native rangewestern redcedar is a massive tree. TheNational Champion western redcedaris over 150' tall and nearly 20' indiameter. This species is highly valuedfor its decay resistant lumber and iswidely used for shakes and shingles. Thetree is referred to as the cornerstone ofNative American culture in the PacificNorthwest. Native Americans used thetrunks of western redcedar for dugoutcanoes and pounded the tree’sstringy bark smooth for clothing andeven diapers for their infants. Whiletoday most parents prefer Pampersto pounding bark, there are manyT. plicata cultivars that are used inlandscaping.‘Elegantissima’: This cultivar is ratedas an intermediate grower by theAmerican Confer Society (6"-12"per year). Chub notes: “This is anupright form that is doing very well atthe Heartland Collection in Clinton,Iowa.” (Zone 5)‘Virescens’: Another T. plicata withan upright habit; dark green tree withan elegant form (Variously listed asZone 4 or 5)‘Excelsa’: Another of Chub’s favoritesthat is doing well at the HeartlandCollection (Zone 5)Thuja occidentalis: Easternarborvitae or northern white-cedaris the eastern cousin of T. plicata.The main range of northern whitecedarextends through the southernpart of the eastern half of Canadaand the adjacent northern part ofthe United States. In Michigan thisspecies occurs throughout Michigan’sUpper Peninsula, in the northern halfof the Lower Peninsula, and along theLake Michigan shore. As mentionedpreviously, this species includes a widearray of cultivars that range in sizefrom dwarf conifers to large trees andspan the range of forms from creepingto columnar. A note of caution, manypopular globe forms of arborvitae suchas ‘Golden Globe’ and ‘Rheingold’ areattractive landscape plants when youngbut often have trouble withstandingsnow-loads as they get larger. Many ofthe upright forms will hold up betterthrough years of Michigan winters.‘Degroots Spire’: This columnarform can be planted as a singlespecimen or used in narrow situationsfor screening. (Zone 4)‘Smaragd’: The trade name is oftenlisted as ‘Emerald Green’. This isa dark green, upright to fastigateform. Chub notes: “This is the onlyarborvitae to crack my list of 25favorite conifers.” (Zone 4)‘Hetz Wintergreen’: Conical,narrow, upright, robust growing, withcompact bright green foliage; tendsto grow with a strong central leaderwithout special training; excellentyear-round screen (Zone 3)‘Sunkist’: Striking bright yellow togolden; fast growing, dense, broad,conical plant; one of the best in thiscolor class; Chub notes: “It’s a dandy.Train to a single leader.” (Zone 3)‘Holmstrup’: Upright, intermediategrower (6"–12" per year); mediumgreen color; Chub notes: “Needto keep this as a single leader whenyoung. If you let it do it’s own thing,you’ll have trouble with heavy, wetsnows.” (Zone 4)‘Recurva Nana’: Dark green witha mounding form; Chub notes:“One of the best. Less problem withsnow loads than many of the globeforms.”(Zone 3)Juniperus: This genus includesabout 50 species, 11 of which arenative to North America includingEastern redcedar (Juniperusvirginiana) and Rocky Mountainjuniper (J. scopulorum). Both speciesare commonly grown in conservationnurseries and they are important treesfor conservation forestry plantingssuch as windbreaks and living snowfences. Eastern redcedar wood is highlyvalued for its scent and decay resistance.And, of course, juniper berries areresponsible for the characteristic flavorof gin. Although named cultivars of J.virginiana and J. scopulorum have beendeveloped, most of the Junipers in thelandscape trade are exotics.Juniperus squamata‘Prostrata’: Prostrate, groundcoveringform with blue foliage that33

eventually mounds in the center;Chub notes: “This has proven one ofthe best prostrate forms of junipers forthe Midwest because of its resistanceto Phomopsis tip blight.” (Zone 4)Juniperus horizontalis: Thisspecies includes nearly 60 cultivars butmany begin to look shabby with agedue to Phomopsis blight.‘Blue Rug’: This is a nice blue-green,ground-hugging juniper for spillingover rocks or as a perimeter plant.(Zone 3)‘Mother Lode’: Bright yellow groundhugging form; excellent groundcover;relatively low-maintenance onceestablished (Zone 3)‘Venusta’: Striking prostrate form(Zone 5)Juniperus chinensis: Often fastgrowers; Chub notes: “Be careful withchinensis, they often get too big andcan overwhelm a landscape.”‘Saybrook Gold’: Gold colorof the new growth is set againsta background of green and goldvariegation on older needles; slightorange cast to the winter color;(Zone 4)‘Robusta Green’: Versatile anddurable landscape plant for accent,windbreak or screen for narrowspaces; irregular columnar form;(Zone 4)Juniperus communis‘Effusa’: A spreading juniper withshiny foliage that grows 15"–18" tall;(Zone 3)‘Compressa’: Very narrow uprightform; slow growing (1"–6" year); agood choice for rock gardens; (Zone4)Juniperus sabina‘Calgary Carpet’: Compact,spreading evergreen with attractivesoft green foliage; excellent lowgrowingaccent shrub; (Zone 3)‘Skandia’: spreading, denselybranched ground cover useful forborder or rock garden accent; verydurable in the landscape; holds itsbright green color well throughwinter (Zone 3)True Cedars. Although many membersof the family Cupressaceae are commonlyreferred to as cedars, botanically speakingnone of them can truly call themselvescedars. True cedars (genus Cedrus) areneedled conifers that are actually membersof the pinaceae family. Cedrus species arecharacterized by needles borne on shortshoots in tufts of 20–30, much like larches.The genus includes four species: deodarcedar, which is a popular ornamental inEurope and milder parts of the US suchas the Pacific Northwest; Atlas cedar(Cedrus atlantica), Cypress cedar (Cedrusbrevifolia) and Cedar of Lebanon (Cedruslibani). Cedars are large stately treesand their foliage gives them a uniquecharacteristic. Unfortunately, cold wintertemperatures limit the use of true cedarsin Michigan. A subspecies of Cedruslibani (ssp. stenocoma) is hardy to zone 5and there is a wonderful, large specimenat Hidden Lake Gardens in Tipton,Michigan.Thuja occidentalis ‘Degroots Spire’Justin “Chub” Harper is widelyknown as one of the leading experts ongarden conifers in the United States. TheHarper Collection of Dwarf and RareConifers at MSU’s Hidden Lake Gardensis nationally recognized. Each “ConiferCorner” includes Chub’s notes on hisfavorite (and not so favorite) conifers.34 The Michigan Landscape