CMG GardenNotes #631 Tree Placement: Right Plant, Right Place

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1 CMG GardenNtes #631 Tree Placement: Right Plant, Right Place Outline: Tree placement in landscape design, page 1 Trees and energy cnservatin, page 3 Maximizing winter slar heating, page 3 Maximizing summer cling, page 3 Nise abatement with trees and shrubs, page 6 Other envirnmental benefits f trees, page 6 Grwing space, page 7 Rting space, page 7 This publicatin utlines cnsideratins fr tree placement in the hme landscape. The average life f a tree in the landscape is nly eight years due t pr design and planting techniques. Hmewners and landscape designers ften place trees in situatins where trees have little chance t establish and thrive. Successful tree planting and establishment need attentin in these five areas: Functinal design Plant selectin Pre-plant handling Planting techniques Pst-planting care Tree Placement in Landscape Design In landscape design, placement f trees needs careful cnsideratin t functin and design elements. Trees are typically the majr plant structure in a landscape. Trees give architectural frm and rganizatin t space. In landscape design, trees shuld nt be randmly placed arund the prperty. Rather, place trees as specimens, grup plantings, r mass plantings. Specimen trees The individual tree becmes the landscape feature. It is set ff frm ther trees and plant materials by unique spacing, frm, clr, and/r texture. Specimen trees are ften, but nt always, a fcal pint in the design. 63I-1

2 Grup plantings In grup plantings, the trees as a unit becme the landscape feature. Grupings are ften, but nt always, the same species. In grup plantings, d nt mix cntrasting frms. Mass plantings In mass plantings, individual trees lse identity and appear as ne larger unit in the design. A grup planting may grw int a mass planting as trees mature. Trees serve several key rles in landscape design. They ften define space. Their spreading branches create a canpy that frms a ceiling fr an utdr rm. Because we spend a lt f time indrs, peple are mre cmfrtable with this utdr ceiling effect. [Figure 1] Figure 1. Trees create a cmfrtable utdr living space with their ceiling effect. Trees are used t frame and mask views. Vertical views are effectively framed with trees n bth sides. The yard shuld flw int the view. Avid specimen plants that draw attentin away frm the view. [Figure 2] Figure 2. In framing a view, allw the yard t flw int the view. When framing a huse, cnsider trees in frnt and t the sides as well as trees that can be viewed ver the rfline. Fr framing, use the pint f reference frm which mst peple wuld view the huse rather than straight n. [Figure 3] Figure 3. When framing a huse, cnsider hw thers wuld lk at the hme rather than straight n. Trees and Energy Cnservatin Tree placement can play a significant rle in energy cnservatin. Winter sun entering suth-facing windws can effectively heat many hmes. Summer shade n suth- and west-facing windws prvides summer cling. In evaluating shading and heating patterns, be aware that shade patterns change with the seasn and with the latitude. [Figure 4] Figure 4. The shade pattern changes with the seasn and with latitude. 63I-2

3 Maximizing Winter Slar Heating Hmes with suth-facing windws have a great ptential t capture winter slar heat. In the winter, deciduus tree branches intercept 20-55% f the sun s radiatin. Fr winter energy cnservatin, avid placing trees where they wuld shade the windws in the winter, and pen drapes t allw the sun s energy int the hme. Winter shade patterns are large, apprximately 2½ times the mature height f the tree at Clrad latitudes. [Figure 5] Figure 5. Fr hmes with suth-facing windws, tree placement can cmprmise winter heating ptential. Maximizing Summer Cling In the summer, trees blck 70-90% f the sun s radiatin n a clear summer day. When prperly placed, trees can reduce air cnditining demands by 10-30%. Alng the Clrad high plains and muntain cmmunities, where temperatures typically cl in the evening, shading a hme may adequately mderate temperatures withut the expense f air cnditining. [Figure 6] Figure 6. Carefully placed trees can reduce hme cling csts by 10-30%. Evaptranspiratin accunts fr 70-80% f the cling benefit. Under dry cnditins (including water restrictins that prhibit landscape irrigatin) evaptranspiratin shuts dwn, phtsynthesis stps (trees live ff carbhydrate reserves), and the cling effect is reduced. Cmmunity temperatures may rise significantly when landscape irrigatin restrictins prhibit utdr watering. Shading the Huse In shading the huse, there is a 2-3 hur lag time n sun heat hitting the huse and the huse becming extremely ht. Shading pririties at Clrad latitudes include the fllwing: 1. Shade windws n suth and west 2. Shade suth walls 3. Shade west walls 4. Shade air-cnditining units 63I-3

4 Shading Pavement As illustrated in Figure 7, a paved area stres apprximately 50% f the sun s energy. In cmparisn, a grass area nly stres 5% f the energy and uses 50% fr evaptranspiratin, resulting in a cling effect. This cling effect is nly peratinal when the grass has water fr active grwth. Figure 7. The sun s energy Anther imprtant cling technique is t shade pavement and ther heat-string materials like the pati and driveway. Als, minimizing paved surfaces helps keep the living area cl. [Figure 8] Figure 8. Fr cling, shade heatstring areas and minimize heat-string surfaces. Trees and ther plant materials may als be used t shield the living space frm stred and reflected heat. [Figure 9] Figure 9. Use trees t cl the air between the heat-string surface and living space. Shading Streets Older cmmunities with tree-lined streets are nted fr the pleasing, inviting surrundings that street trees create. Shaded streets are 10 F t 40 F cler. 63I-4

5 Hwever, street trees are ften predispsed t pr grwth and limited life spans due t pr sil cnditins. Tree rts can generally spread under a sidewalk int pen lawn areas beynd. Rt spread under a street is dependent n the sil prperties created during rad cnstructin. When the planting strip between the street and sidewalk is less than eight feet wide, tree health, vigr, and life span will be reduced. In mst cmmunities, planting strip width is set by the city rdinance in effect at the time f develpment. An effective alternative fr tree-lined streets is t plant trees in the lawn eight feet in frm the street. This may give trees a better sil envirnment fr rt grwth, resulting in imprved tree vigr, grwth, and lngevity. In this situatin, trees are als less likely t be hit by cars r damaged frm rad repairs. Eliminating the narrw planting area between the street and sidewalk is als an imprtant water cnservatin technique as the mw strip is difficult t irrigate efficiently. Nise Abatement with Trees and Shrubs Tree and shrub hedgerws (planting belts) effectively abate nise pllutin. T be mst effective, place the hedgerw clse t the nise surce away frm the living area. The hedgerw shuld be twice as lng as the distance frm the nise surce t the living space. T be effective, the hedgerw needs t be dense. A few trees and shrubs here and there d little t abate nise. [Figure 10] Figure 10. Fr effective nise abatement, place plant belt next t nise surce. Other Envirnmental Benefits f Trees In a study by the USDA Frest Service, the 16,000 street trees in Frt Cllins, Clrad, cntribute $2.2 millin in envirnmental benefits. The cmmunity frest has many imprtant benefits, including: Energy saving frm heating and cling Nise abatement Carbn dixide reductin In a Sacrament Califrnia study, the carbn sequestratin frm the cmmunity frest mre than ffsets the inputs frm human activity. Air-pllutin abatement Hydrlgy (strmwater runff) Prperty values The USDA Frest Service evaluated the benefits f cmmunity frests. Fr each dllar that a city invests in a cmmunity tree prgram, large trees return $1.92 in envirnmental benefits. Medium-size trees return $1.36, while small trees return $1.00. T maximize envirnmental benefits, the gal in cmmunity frestry is t have 63I-5

6 50% f the land cvered with tree canpy. That is, if we were t lk dwn frm an airplane, trees wuld cver 50% f the area. Here in the west, we have a great need t plant mre trees in ur cmmunities. In wded cmmunities, the need may be t thin the frest. T maximize the benefits f ur cmmunity frests, hmewners and cmmunity leaders need t recgnize that the primary benefits ccur frm large trees. We need t enhance effrts t prtect and maintain large trees. We need t plan fr large trees in landscape design. Small specimen trees may add t the landscape design, but large trees prvide significantly mre envirnmental benefits. We need t plant trees in situatins where they have the ptential t reach a mature size with lngevity. Grwing Space Size is a primary cnsideratin in tree selectin. Trees shuld fit in the available grwing space withut pruning. This is f primary cncern under utility lines as the utility has the right-f-way. Frequent pruning required t keep utility lines clear adds t ur utility rates. As discussed previusly, envirnmental benefits are significantly greater fr larger trees. Cnsider large tree species whenever the space allws. With prper structural training, large trees have minimal ptential fr strm and wind damage. Hmewners ften desire fast-grwing trees. Hwever, fast-grwing species are typically mre prne t insects, diseases, and internal decay. Fast-grwing species typically have shrter life spans. Rting Space Rting space shuld be a primary cnsideratin in tree selectin. The mature size, grwth rate, and lngevity f a tree are directly related t the available rting space. Many trees in the landscape are predispsed at planting t a shrt life and limited grwth ptential due t pr sil cnditins and limited rting space. Figure 11 shws the relatinship between rt space and ultimate tree size. Fr example, a tree with a 16-inch diameter requires 1,000 cubic feet f sil. On a cmpacted, clayey sil, rting depth may be restricted t 1 ft r less, and spread wuld be an area 36 feet in diameter. Anything less will reduce tree size, grwth rates, vigr, and lngevity. [Figure 11] Figure 11. Ultimate tree size is set by the rting space. 63I-6

7 Tree rts can generally crss under a sidewalk t pen lawn areas beynd. The ability f rts t crss under a street depends n the rad base prperties. A gd rad base des nt typically supprt rt grwth due t cmpactin and lw sil xygen levels. The rting area des nt need t be runded; it can be abut any shape. Trees can share rting space. Trees in Planters Trees are ften placed in planters and ther sites with limited rting ptential. If the rts cannt escape the planting site (rt vault) int ther sils: 1. Rt grwth slws when the rt vault area is filled. 2. Tree grwth slws. 3. Tree declines. 4. Rutine replacement is required. The average life f trees in sidewalk planters and ther restricted rt vault sites is 8 years. Hme gardener and landscape designers need t understand that with restricted rting space, grwth ptential, and lngevity are reduced accrdingly. Authrs: David Whiting (CSU Extensin, retired) with Carl O Meara (CSU Extensin). Artwrk by David Whiting; used by permissin. Clrad Master Gardener GardenNtes are available nline at Clrad Master Gardener training is made pssible, in part, by a grant frm the Clrad Garden Shw, Inc. Clrad State University, U.S. Department f Agriculture and Clrad cunties cperating. Extensin prgrams are available t all withut discriminatin. N endrsement f prducts mentined is intended nr is criticism implied f prducts nt mentined. Cpyright Clrad State University Extensin. All Rights Reserved. CMG GardenNtes may be reprduced, withut change r additins, fr nnprfit educatinal use with attributin. Revised Octber I-7