The plantable sector of the segmental retaining wall industry is now realizing new life. Since 1984, segmental retaining walls have flourished worldwide with a few foresighted entrepreneurs having perfected systems that can be vegetated. While the split face and tumbled textures of the conventional segmental retaining walls are more desirable than the stark, monolithic appearance of conventional concrete poured or cinder block retaining walls, the consumer ?EUR??,,????'??? often the architect ?EUR??,,????'??? wants more. The discriminating owners and design professionals are demanding a soft, natural looking green wall that disappears into the landscape. In order for planted walls to be successful, considerable thought and planning is required in selecting an appropriate wall system. The following paragraphs cover selection criteria for the various aspects of planning for plantable wall systems... ?EUR??,,????'???? Wall drainage - Most wall systems incorporate permeable soils for construction of the reinforced soil system. In some cases, drainage or transition soil is used behind the retaining wall blocks. While not needed for all wall systems, the existence of a granular drainage layer behind the retaining wall fascia can be provided for a variety of reasons including drainage of excess moisture, facilitating compaction near the wall face, and protection against soil loss via piping. For systems that have a planting medium contiguous with the drainage system, it also provides drainage that most plants need and further prevents planted materials from developing ?EUR??,,????'??wet feet.?EUR??,,????'?? ?EUR??,,????'???? Retaining and dissipating moisture - The ability of a wall system to ?EUR??,,????'??retain?EUR??,,????'?? moisture within the planting zone or to ?EUR??,,????'??draw?EUR??,,????'?? moisture from the mass of the retaining structure should be considered during the wall selection process. Conversely, during wet periods, the system must be able to dissipate or drain moisture away from the planting medium. Without the ability to dissipate, retain or draw moisture, the vegetation is likely to dry out, rot, drown, or burn. In any event, the wrong mix results in disaster. ?EUR??,,????'???? Temperature extremes - The face of a segmental retaining wall typically undergoes large temperature extremes. When exposed to direct sunlight, exposed wall fascia blocks can get very hot ?EUR??,,????'??? especially if the fascia units are dark in color. A wall that has been heated by daytime sun can remain hot long after sunset. In the spring, when the heat of the sun is needed to nurture developing plants, the heat absorption properties of the wall may be a welcome phenomenon. The prolonged heat collected by the wall facing during the day and released at night can enhance germination and advance plant growth. ?EUR??,,????'???? Fertilizing ?EUR??,,????'??? Soils placed within the facing units can be ?EUR??,,????'??spiked?EUR??,,????'?? with fertilizer during construction. A time-released, environmentally responsible fertilizer is often chosen. Broadcasting the fertilizer by hand during construction is easy and inexpensive. The longevity and effectiveness of the fertilizer is a function of release rate, composition, application rate, and planting soil composition. Fertilizers broadcast into the planting soils placed during construction have maintained many walls in a healthy green condition for periods in excess of 10 years without follow-up fertilizing or supplemental soil amendments. ?EUR??,,????'???? Irrigation considerations - While it is likely that a drainage system will be provided in most segmental walls, irrigation water should be used sparingly and in such a manner that will minimize the potential for saturating the soils of the wall mass. ?EUR??,,????'???? Attaching irrigation lines to the wall - Where the wall face is too large to irrigate from one line, either vertical or horizontal irrigation circuits can be ?EUR??,,????'??hung?EUR??,,????'?? from the wall face. Attachment of irrigation lines to the wall face can be accomplished by a combination of anchoring methods including supporting on block ?EUR??,,????'??ledges?EUR??,,????'??, anchoring to hooks driven into the wall mass, or other mechanical means of connection to the wall structure. Irrigation attachment suggestions are typically available from the wall provider. ?EUR??,,????'???? Spray, bubble, mist or drip - Spray type irrigation systems perform well on walls that exhibit large face areas. Bubbler type irrigation heads and drip irrigation systems work well where discrete watering pockets can be identified. Mist systems work well where small areas need to be covered. ?EUR??,,????'???? Erosion within facing - Care should be exercised to minimize access of excess irrigation water into the reinforced soils of the wall. For that reason, facing systems which shed excess water to lower facing elements or to the internal wall drainage system are preferred over those that enable irrigation or precipitation moisture to run vertically through the wall unit stack and carry soil vertically through the block units. Facing units without bottoms are highly prone to this type of erosion and hence pose high maintenance risks, not to mention the potential for adverse structural concerns. ?EUR??,,????'???? Irrigation visibility and UV - Face-mounted irrigation lines may initially be visible; however, they will disappear as vegetation becomes established. If UV is deemed to be a long-term concern, UV resistant pipe should be considered. Once established, the vegetation will help to protect the irrigation lines from the degradative effects of UV, thus prolonging the ?EUR??,,????'??rated?EUR??,,????'?? life of the ?EUR??,,????'??naked?EUR??,,????'?? irrigation line. ?EUR??,,????'???? Planting schemes - Planting schemes for fully plantable segmental retaining walls are similar to planting schemes used to minimize the visual impact of conventional, non-plantable walls. In general, wall systems with intermittent vertical planting courses (partially planted wall systems), utilize tall plants near the wall base, hanging plants near the wall crest and fill-in plants elsewhere. In the case of fully plantable walls, hanging species planted near the wall crest are used in conjunction with fill-in species for the mass of the wall. ?EUR??,,????'???? Consider the plants - Local vegetation is typically the planting of choice. Beyond that, the directional exposure of the wall face must be taken into consideration when selecting specific plant species. Considerations such as lighting conditions, growth patterns, root structure, moisture requirements, color, etc. provide a first pass at suitable vegetation choices. ?EUR??,,????'???? Unplanted walls ?EUR??,,????'??? Plantable retaining walls offer maximum aesthetic value when planted. However, they do not NEED to be planted. They will perform the retaining function just fine in an un-vegetated condition. If planting is desired at a later date and the above considerations have been pondered, planting can be conducted at any time after the wall is completed with minimal impact or financial consequence. However, an increase in erosion from the soil pockets may be observed during the first few rain events. With the exception of the facing systems that do not contain a bottom in each block, the erosion from the face will dissipate quickly and likely sprout volunteer vegetation, whether wanted or not. If vegetation is to be discouraged, an appropriate pre-emergent or other plant inhibitor can be applied to the soil planting pockets. ?EUR??,,????'???? Placement of plantings with large root balls near the wall crest ?EUR??,,????'??? While not unique to segmental retaining walls having vegetated facings, deep excavations near the crest of the wall should be avoided. Deep excavations required to accommodate a large root ball may sever near-surface geosynthetic reinforcements. While it is unlikely that such excavations will critically impact the structural integrity of the wall, some local, near-surface wall instability may result. Further, trees and large shrubs which are planted near the crest of the retaining wall will not have the benefit of full lateral resistance during periods of transient horizontal loading such as those imposed by wind. ?EUR??,,????'???? Excavations near the wall crest - If large trees, large shrubs, spas, pools, wall foundations, patio footings or other features requiring deep excavations are planned for post wall construction near the wall crest, the retaining wall can be designed such that the upper layer or two of geosynthetic reinforcement is maintained at a reasonable and practical depth beneath the finished grades of the wall crest. Coordination with project design professionals during design is required to ensure that the potential for excavating through the reinforcement can be avoided. ?EUR??,,????'???? Installation of structures near the wall crest ?EUR??,,????'??? Deed restrictions are recommended to alert existing and future owners that excavations into the reinforced soil mass may encounter structural elements of the wall. Additional considerations are included below. Damage from driving/drilling postholes is typically minimal and not normally structurally significant. However, it is strongly advised that the wall designer and/or geotechnical engineer of record be consulted prior to driving, drilling, or otherwise excavating near the crest of a geosynthetically reinforced segmental retaining structure. Evaluation by the design professionals will be able to determine the most desirable method of supporting structures near the wall crest. Deep linear excavations parallel to and near the wall crest (possibly used for installation of utility lines) may sever geosynthetic reinforcements and hence should never be conducted without prior approval of the wall designer and/or the geotechnical engineer of record. If utility lines must be installed within the reinforced soil mass, they should be constructed such that minimal impact of the geosynthetic reinforcement is affected. A suggestion to minimizing impact includes relocating the collector or main utility lines to a position behind the reinforced soil mass with lateral/feeder/supply lines oriented perpendicular to the wall face. ?EUR??,,????'???? Vectors ?EUR??,,????'??? A green vegetated wall may provide an attractive environment for a variety of vectors including squirrels, mice and birds. While the green, vegetated surface may provide a great habitat for vectors, it also provides a near-natural environment within which predators can hunt. In essence, the natural riparian area and habitat for wildlife is extended by the existence of a vegetated wall. This is arguably a better proposition than the sterile, stark, unnatural surface of a conventional concrete structure. ?EUR??,,????'???? Long-term maintenance ?EUR??,,????'??? Long term maintenance requirements for the planting materials and irrigation system are obvious. Fertilizing will be required infrequently and will be a function of fertilization program. In some cases fertilizing may be required yearly (spray applications) while other programs may require frequencies extending to a decade or more. Irrigation head maintenance is typically conducted on an as-needed basis. However, periodic visual observation (at least yearly) of the operating irrigation system is advisable. While extremely infrequent, broken lines must be dealt with as soon as they are discovered. Maintenance of plant materials includes simply replacing those materials that become overgrown, unsightly, dead, or otherwise undesirable.