Biological Erosion Control With Vetiver Grass On A Steep, Dry Fill Slope

~ Level 3 – Design & Implementation ~

Level 3 – Biological Retaining Wall & Natural Stone Pathway

Location: Thousands Oaks, CA

Project Details: This dry, inaccessible, fragile fill slope was progressively eroding towards the foundation of the house with each passing year when we first visited. The slope is directly south-facing and very steep (55-60% grade), making it largely impassable and dangerous to work or move on. Between ground squirrel activity, the family dog, and occasional human traversing of the slope to a lower gate to take the dog for a walk, the slope was de-vegetated except for a few small patches of Aptenia.

Needs: The primary needs of the design were to stop the erosion from progressing further towards the house, to create a safe way to access the slope and to create a beautiful backdrop to the back deck space. Secondary needs included maintaining some visual privacy between the deck and the public hiking trail adjacent to the property (needed view screen at least four feet high) while also maintaining the big sky view to the South and West (no large trees).

Constraints: Water is an increasingly scarce resource in Southern California, so any plantings had to be geared to low-to-no summer water. Between drought hardiness and the need to halt erosion, deep-rooted or mat-forming root types were the only types of plant considered. Limitations on watering frequency also dictated that a drought-hardy plant be used.

Looking up at the hillside before starting the stone pathway.
Mid-slope looking across. Soils were sandy and full of concrete rubble.
Looking downslope where the pathway is going to meet the level yard. Green flags mark proposed rock pathway.

Work Performed

  • Natural stone pathway installed to provide safe and aesthetically pleasing cross and down slope access. Stones were gravity-glued (fitted to place and anchoring one another).
  • Seven lines of vetiver planted on contour at 4″ centers to create biological retaining wall effect.
  • Automated irrigation system for vetiver establishment and maintenance installed.
  • Follow up seasonal vetiver cuts to help all plants establish evenly.

Project Install Video

Vetiver Grass After 6 Weeks

Vetiver Grass After 15 Months