Soil Mix and Plant Materials for Washington Bridge

Stress resistant plants and lightweight growing substrate mixtures were developed for use on roofs for environmental, economic, and aesthetic benefits as greenroofs. The goal of this study was to evaluate different greenroof plant and substrate combinations to determine if extensive greenroof technology could be modified for low-cost reduced-maintenance bridge and roadside planters designed for the Rhode Island Department of Transportation (RIDOT). Ten plant taxa: "Allium schoenoprasum" L., "Delosperma aberdeenense" (L.) Bolus., "Drosanthemum hispidum" (L.) Schwant., "Jovibarba hirta" (L.) Opiz. 'Emerald Spring' (Syn. "Sempervivum hirta" L.), "Orostachys iwarenge" Hara. (Syn. "Orostachys boehmeri" Makino; "Sedum boehmeri" L.), "Sedum hispanicum" L. 'Immergraunch', "Sedum japonicum" Sieb., "Sedum spurium" Bieb. 'John Creech', "Sempervivum" L. var. Specialty Blend, and "Talinum calycinum" Engelm., and three growing substrate mixtures suitable for greenroofs: Growing Substrate 1 (GS1; 10% field soil, 10% compost, and 80% Hydrocks™), Growing Substrate 2 (GS2; 20% compost and 80% Norlite), and Growing Substrate 3 (GS3: 40% field soil, 20% compost, and 40% Hydrocks™) were evaluated in mesocosms for use in concrete planters for bridge-top plantings. Plant area, plant height, growing substrate water content, temperature, nutrition, and weediness were used for comparison. "A. schoenoprasum D. aberdeenense, D. hispidum, S. hispanicum 'Immergraunch', S. japonicum" were replaced due to winter injury or lodged stems. These five taxa were replaced with "Allium senescens" (Schrad.) Reg. var. glaucum., "Hylotelephium cyaneum" (Rudolph) H. Ohba. (Syn. "Sedum cyanum" Rudolph) 'Rose Carpet', "Sedum kamtschaticum" Fisch. 'Weihenstephaner Gold', "Sedum lineare' Thumb. 'Golden Teardrop', and "Sedum stenopetalum" Pursh. Plants growing in GS2 or GS3 had similar area and height increases and water content, while those growing in GS1 yielded the least increases over two growing seasons. GS2 had less weed growth, greater porosity, and higher nutrient levels than GS3.

  • Corporate Authors:

    University of Rhode Island, Kingston

    Department of Plant Sciences
    Kingston, RI  United States  02881

    Rhode Island Department of Transportation

    Research and Technology Development
    Two Capitol Hill
    Providence, RI  United States  02903

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • Maynard, Brian
    • Castrataro, Nicholas
    • Johnson, William
  • Publication Date: 2006-6


  • English

Media Info

  • Media Type: Print
  • Edition: Final Report
  • Features: Appendices; Figures; Photos; References; Tables;
  • Pagination: 93p

Subject/Index Terms

Filing Info

  • Accession Number: 01044280
  • Record Type: Publication
  • Report/Paper Numbers: FHWA-RIDOT-RTD-06-2
  • Contract Numbers: SPR-228-2252
  • Created Date: Mar 6 2007 6:12PM