Table 1.

Design of three types of planting pit used in the experiment.

Type 1Type 2Type 3
Pit dimension (m)1.2 × 1.2 × 1.01.2 × 1.2 × 1.01.2 × 2.8 × 1.0
Soil compositionTopsoilUrban soilzSpecial interlocking root cell systemy filled with topsoil.
Irrigation setupnoneAn irrigation pipe of 895 mm × 3 m length, outside of the root barrier at 200–300 mm depth was installed.Same as Type 2.
Root barrierOnly re-root 300 linear root barriers were wrapped around top of root ball.With linear root barrier a terram 3000 permeable geotextile layer was laid to stop upward root growth.Same as Type 2.
Paving materialFinished off with 100 mm depth of composting mulch.50 mm laying course of 6 mm washed graded aggregate was laid. Finally Marshall ‘Priora’x concrete block paving was used to seal the pit.Same as Type 2.
  • zUrban soil is a mix of 50% sand and 50% topsoil; overall texture is 10%–12% clay, 10%–12% silt, and 75%–80 % sand content.

  • yRoot cell system (Green-tech Ltd, York, UK): Each cell is 250 mm × 250 mm × 90 mm in size, made of recycled high-density polyethylene (HDPE) and has a load-bearing capacity of 80 tonnes per m2, each cell weighs 0.38 kg and has 92% empty space inside.

  • xMarshall ‘Priora’ concrete block: These are special zigzag bordered blocks with approximately 6 mm of gap between each block which allows 1.8 L S−1 m−2 water through them.