for background information and some disclosure , reference is made to the above - specified u . s . pat . no . 4 , 019 , 279 , issued apr . 26 , 1977 . said patent is hereby incorporated by reference herein . in the present specification and claims , the words &# 34 ; inner surface &# 34 ;, &# 34 ; inner side &# 34 ;, etc ., of a panel or barrier denote that side closest to the tree whose roots are being guarded against . conversely , the &# 34 ; outer surface &# 34 ;, etc ., of the panel ( or barrier ) is that side farthest from such tree . it is preferred , but not essential , that each panel be identical to each other panel . in the panels described in the present specification , such is the case . as shown in fig2 each root - control barrier panel p is square or rectangular , and may be horizontally or vertically elongate . each panel p is formed of such material , and has a thickness such that , it may not be penetrated by tree roots . preferably , each panel is a sheet 10 of synthetic resin having a thickness of about 0 . 080 inch . one side of the sheet is preferably devoid of protuberances , while the other side of each panel has a plurality of spaced vertical ridges ( ribs ) 11 . preferably , the ridges are spaced about six inches apart , are 0 . 060 inch thick , and extend perpendicularly to the surface of the panel for about one - half inch . the inner surface of each panel is smooth . in the best mode , there are horizontal ledges 12 disposed between ridges 11 and spaced vertically relative to each other . such ledges are ground locks adapted to be engaged by tree roots , on the upper surfaces of the ledges , so that the tree roots prevent such ledges and thus the panel from moving upwardly in the earth . reference is made to u . s . pat . no . 5 , 070 , 642 , which is hereby incorporated by reference herein . each panel has a height , preferably , of about twelve inches , or about eighteen inches or more . preferably , each panel is injection molded of polyethylene , or polypropylene . as shown in fig6 each end of each panel is formed integrally with a vertical channel 13 and vertical double - flange 14 for use in connecting adjacent panels p together . the flanges 14 and channels 13 are associated with connectors 16 in the form of two channel - like elements that , in the preferred embodiment , are secured to each other at a living hinge 17 . stated otherwise , two substantially closed channels are connected to each other at a living hinge 17 and are adapted to be slid simultaneously over the double flanges 14 of adjacent panels 13 , to connect the adjacent panels together in a manner such that the panels may be selectively in the same plane or different planes . reference is made to my copending patent application ser . no . 07 / 682 , 581 , filed may 8 , 1991 , which application is hereby incorporated by reference herein . referring to fig7 another end connector construction is shown which does not have any capability of permitting the adjacent ends of panels p to get out of the same plane . this connector , numbered 18 , is an extrusion formed of two substantially closed channels having a rigid wall 19 therebetween and forming part of each of the channels . as best shown in fig2 - 4 , a double rail 21 is molded integrally on the upper edge of sheet 10 , in parallel relationship to the longitudinally axis of the connected panels p . double rail 21 has an upper cross - member 22 and a lower cross - member 23 separated by a vertical web 24 . web 24 lies in the same plane as that of sheet 10 , whereas each cross - member 22 , 23 lies in a horizontal plane perpendicular to such vertical plane . each cross - member 22 , 23 is formed of two coplanar flanges , one extending to the right from vertical member 24 ( fig4 ), and the other extending to the left therefrom . as shown , the outer edges of each cross - member are rounded . in the preferred embodiment , the width of each upper rail or cross - member 22 is 3 / 8 inch . the lower rail or cross - member 23 has the same dimension . the vertical distance between the underside of upper cross - member 22 and the upper side of lower cross - member 23 is 1 / 4 inch . the vertical thickness of each rail or cross - member 22 , 23 is 0 . 060 inch or 0 . 070 inch . these dimensions are given by way of illustration , not limitation . channels 25 are formed on each side of vertical member 24 , since member 24 ( preferably ) has the same thickness as that of sheet 10 whereas each cross - member 22 , 23 has a width greater than the thickness of web 24 or of sheet 10 . referring next to fig1 the combination of the invention further comprises a sidewalk 26 or other static structure ( hardscape ) which is supported in the earth 27 in spaced relationship from a tree 28 that is growing in the earth 27 . tree 28 is of a type having roots 29 capable of growing beneath sidewalk 26 and lifting and / or cracking it . the panel p is disposed vertically in the earth , with the lower surface of lower cross - member 23 resting upon the upper surface 31 of the earth ( namely , at grade ). then , as shown in fig4 upper cross - member 22 is disposed a predetermined short distance above lower cross - member 23 . upper cross - member 22 performs the various functions stated above , namely sun protection so as to retard greatly deterioration of the synthetic resin , protection against trimmers , prevention of cutting of the feet of children , etc ., etc . lower cross - member 23 seats on the grade surface 31 and acts as a stop to determine the precise elevation of the panel p in the earth -- making sure that the upper cross - member 22 is at the same desired elevation above grade 31 . very importantly , the lower cross - member 23 insures that surface - growing roots remain at or below the surface ( grade 31 ) in almost all cases . for example , referring to fig4 if a root 29 from tree 28 goes into a region of sheet 10 of a panel p adjacent a rib or ridge 11 , the root 29 cannot turn upwardly because of cross - member 23 , but will instead turn downwardly to grow down in the region where ridge 11 meets the inner surface of sheet 10 . only when the root grows downwardly to the bottom edge of the panel p may it grow horizontally beneath the panel . however , it is then so far beneath the sidewalk 26 that enlargement of the root over time will not lift or damage the sidewalk . as another example , and referring to fig5 a root 29 from tree 28 engages sheet 10 at a region spaced a substantial distance from a ridge 11 . the root will then turn laterally and grow along the sheet 10 toward a ridge 11 . the root may turn horizontally in either direction , but regardless of which way it turns it will grow into a ridge 11 . as it grows toward a ridge , it may grow upwardly as shown in fig5 but will then engage the underside of lower cross - member 23 instead of , in some cases , growing above grade 31 . eventually , the root engages a ridge 11 and grows downwardly as shown in fig5 . if an occasional root 29 grows above lower cross - member 23 it will merely enter that channel 25 which is facing tree 28 . it will grow along the channel 25 until eventually it dies , being prevented by the upper cross - member 22 from penetrating to the side of panel p remote from tree 28 . in the absence of the present invention , the upper horizontal edge of a series of connected panels was typically slightly above grade . such edge was fully exposed to ultraviolet radiation from the sun , and its exact elevation above grade varied substantially because there was no positive ground - engagement and spacer means to determine the elevation precisely . such upper edge of prior - art panels looked very insubstantial to the home owner or city - employed arborist who contracted for the job . on occasion , the barrier may have been even more insubstantial than the arborist or home owner believed , because a fraudulent installer could cut the strip of connected panels in half horizontally ( along generally the horizontal axis of the connected panels ). in such a situation , and unless the arborist or home owner dug into the earth at spaced points along the elongate strip of panels , there was no way of telling whether or not the full uncut panel was present in the earth or whether the thing present was just about half a strip . it is emphasized that if a string of panels not incorporating the present invention is cut in half horizontally , there are two clean uncut edges . one is the upper , and the other is the lower . thus , it was possible for a fraudulent installer to take the upper one of the cut half - strips and embed it with the clean upper edge uppermost . simultaneously , he could take the lower portion of the cut strip and turn it over and embed it so that the uncut lower edge became the upper edge and was visible above ground . with the present invention , on the other hand , it does no good for any installer to cut any string of panels horizontally , because there is only one rail 21 and that is above the ground where it is readily viewed . let it be assumed that a sidewalk 26 ( for example ) is already in place . a narrow trench is then dug along the edge of sidewalk 26 , to the desired depth such as twelve , eighteen , or twenty - four inches . if a tree ( such as tree 28 ) is already in place and has roots that extend beneath the sidewalk 26 , the trench - digging operation is so conducted as to cut the tree roots and thus achieve desired root pruning . if no tree is already in place , a subsequent step in the method comprises planting a tree or trees in the earth 27 on the side of panel p remote from the sidewalk 26 , but sufficiently close to the sidewalk that ( in the absence of the panel p ) roots from the tree would grow beneath the sidewalk . a substantial number of panels p are then connected together by the connector elements 16 shown in fig6 . the narrow trench is then backfilled with earth up to the grade level 31 and is compressed as by being packed . the operation is so conducted that the lower surface of lower cross - member 23 is at grade 31 as shown and described relative to fig4 . by reference to the grade level in the original soil adjacent the narrow trench , the operator can readily see what the grade should be after the trench has been backfilled -- namely , it should be the same as the original grade . by grasping the upper cross - member 23 at appropriate times during the backfilling or packing operations , the operator readily adjusts the elevation of the string of connected panels p so that the lower cross - member 23 is resting on grade 31 . except as specifically stated below , the apparatus and method of the second embodiment are identical to what is described above , and shown in the drawings , relative to the embodiment of fig1 - 7 , inclusive . thus , relative to the second embodiment only those elements that are different from the embodiment of fig1 - 7 are shown and described . except relative to the differences , the statements made above ( prior to the present subheading ) are applicable here also , and are therefore incorporated here by reference . the differences are shown by fig8 and 9 , which illustrate portions of the apparatus of the second embodiment . elements in fig8 and 9 which &# 34 ; correspond &# 34 ; to elements in fig1 - 7 are given the same reference numerals , except followed in each instance by the letter &# 34 ; a &# 34 ;. this is done without prejudice to the fact that most of the elements of fig8 and 9 are different from those of fig1 - 7 . the embodiment of fig8 and 9 is the preferred embodiment . upper cross - member 22a and lower cross - member 23a are each on one side of sheet 10a . stated otherwise , cross - members 22a , 23a extend inwardly from sheet 10a and from web 24a . preferably , the amount of such inward extension is about equal to the full widths of cross - members 22 , 23 as shown in fig4 . thus , the groove 25a between the cross - members 22a , 23a ( fig8 and 9 ) is substantially deeper than either groove 25 ( fig4 ). each ridge or rib 11a preferably extends up to upper cross - member 22a , as shown , being integral therewith . there is , as illustrated in fig8 preferably no channel adjacent flange 14a . in performing the method using the embodiment of fig8 and 9 , previously - described method steps are performed , following which the root - control barrier is embedded in the earth 27a to the depth of the lower surface of lower cross - member 23a -- which act as a stop means . upper cross - member 22a then shields lower cross - member 23a and one side of web 24a from the sun , and performs the other advantages functions described above . the lower cross - member being relatively wide , it is especially effective in preventing a root , such a root 29a , from growing above grade 31a . any root that does get above the lower cross - member 23a enters groove 25a , soon engages a ridge 11a , and dies . it is emphasized that the panels are so oriented that the cross - members 22a , 23a extend toward the tree 28 whose roots are to be guarded against . the foregoing detailed description is to be clearly understood as given by way of illustration and example only , the spirit and scope of this invention being limited solely by the appended claims .
a tree root - control barrier system formed by a plurality of panels having vertical ridges thereon . then panels are embedded in the earth between a sidewalk and a tree whose roots are to be controlled . upper and lower cross - members are provided on the panels at their upper edges , and perform various functions including sun protection , protection against lawn trimmers , protection against the growing of tree roots above the ground , and others .