TruGro Amends Heavy Clay Soil on UNT Campus

The new Business Leadership Building on the University of North Texas campus is an integral part of their business school. At 180,000 square feet, this structure accommodates four times the number of students than the old building and contains traditional and “smart” classrooms, multimedia learning laboratories, distance learning facilities, a café, study and tutor rooms, and offices for faculty and administrative staff.

The project received gold-level LEED (Leadership in Energy and Environmental Design) certification, which means it met strict standards for design and construction. The landscape was one element of this certification process.

The UNT landscape management staff are big proponents of the EarthKind Environmental Landscape Management System as it pertains to heavy clay soils. This system seeks to improve the growing characteristics of clay with the addition of expanded shale and compost. The expanded shale helps to promote drainage, air exchange and microbial production while the compost provides a fertilizer source. Both products help to retain moisture beneficial to the plant roots. When used with native plantings, this system has proven to reduce irrigation and maintenance costs.

The Process

Consulting with the university horticulture director, the landscape architectural firm of Caye Cook & Associates established a system to rejuvenate the turf and landscape soils. The general process included:

  • Excavation and stockpiling of the best quality topsoil for reuse.
  • Weed removal treatment and grubbing.
  • Loosening all compacted soils to a 10” depth by ripping and tilling.
  • Removal of all non-soil materials (construction debris, buried waste, rocks, vegetation)
  • Re-compaction to industry standards.
  • Placement of 2” of original topsoil along with a few inches of a screened “black soil” and tilled into the 10” loosened clay soil profile.
  • Placement of 3” of expanded shale and tilled into topsoil/loosened clay soil profile.
  • Placement of 3” of a well-aged vegetative based organic compost and tilled into the expanded shale/topsoil/loosened clay soil profile.

Amended Soils Benefit Environment

The amended soils reduce watering by allowing irrigation and rainfall to infiltrate deeper into the profile where less evaporation and drying occurs. Deeper roots are better suited to filter storm drainage and the added air and pore space contributes to less runoff and discharge into storm drainage systems. Expanded shale will improve drainage and, when combined with an organic amendment, provides a long term organic fertilizer to landscape plantings. Caye Cook & Associates designed a drip irrigation system along with a week block and mulch to hold moisture and restrict the growth of weeds. A landscape design rich in native and locally adapted plants rounded out the strategy to reduce annual irrigation and maintenance costs. A second story roof-top garden at the Leadership Building used expanded shale with washed concrete sand and compost in their large container plantings.

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