Raised Plantings

Review Benefits of Plantings in the ROW and In-Ground Plantings

• Above-ground planting structures allow the integration of other design elements such as seating and lighting
• Raised planters create more substantial barriers from vehicles
• Raised planters provide protection from winter salt spray

Review Key Considerations

Review considerations for In-Ground Plantings

• Plant selection should be sensitive to the limited amount of soil available for root growth in a raised planter. Due to the limited soil volume, plants should be more drought-tolerant and will need to be watered more often
• Determine whether a closed-bottom or open-bottom planting area is required as it will impact drainage design and plant selection
• Soil is less insulated in raised planting beds; freeze and thaw cycles will be more extreme in winter; select plants that are one to two USDA zones hardier to survive these conditions
• Any plantings not maintained by DOT, DEP, or Parks will require a maintenance agreement

• Where below-ground constraints restrict the available soil volume
• Where added height and structure is necessary to provide protection to the space or to the plantings

Review design guidance for In-Ground Plantings

Review Key Considerations: Plant Selection

Review DOT's Planted Raised Median Design Guidelines for further information

Soils and Drainage

• Consider the type of soil that will be used. Specify a soil with optimal water and nutrient holding capacity
• Planting beds should be sufficiently wide and deep to provide adequate soil volume for plants: length and width may vary, but in general planting areas should not be narrower than 3 feet; for soil depth provide at least 18 inches for grass or ground cover, 18 to 24 inches for shrubs, and 18 to 30 inches for trees. The soil depth should also relate to the root ball depth at planting – review Key Considerations: Soils. Exceptions may be approved on a case-by-case basis
• Positive drainage below the planting soil is essential. Any impermeable layers of concrete or asphalt must be removed to provide an open-bottom where water and roots have access to existing soil beneath the planting area. Alternatively, appropriately designed weep holes must be included for a closed-bottom soil area. Open-bottomed raised planting areas are preferred where feasible
• Ensure redundant drainage is included for any closed-bottom soil area to ensure failure doesn't result in water-logged soil that will negatively impact plants

Structure and Topography

• Planting beds should generally be limited in height and maintain visual and physical openness
• Raised structures allow for greater variation in topography
• Raised plantings can be designed to creatively accommodate or incorporate required security measures; consider impacts of security infrastructure (foundations, spacing requirements, etc.) on species selection

Environmental and Planting

• The roots of plants will be primarily within the top 12 inches of the surface, and are thus more sensitive to freeze-thaw cycles in the winter. Carefully select species which are cold hardy to at least Zone 6A. For added insulation, provide adequate mulch (2 to 3 inches) at the time of planting and replenish as necessary
• For closed-bottom soil areas, select plants that can tolerate more limited soil volume, periodic drainage issues, and more concentrated nutrient build ups or deficiencies depending on maintenance practices
• Review the Plant Finder for plants that perform well in the right-of-way. Plants should be selected that do not extend beyond the raised planting area and infringe on the sidewalk or roadway. Plants that cascade over the raised edge may be considered. Plant selection must always be made based on site-specific conditions