Upper Pitt Street, Liverpool

With the increasing popularity and demand, in many cases as part of the planning conditions, for green roofs and rain gardens, Green-tree offers a wide range of lightweight green roof and podium substrates, as well as rain garden and bioretention soils, all using our ever-popular British Standard manufactured soil as a base.

In this instance, as Liverpool had no previous experience using rain gardens as a “green solution”, it was proposed to create a test area to demonstrate what could be achieved.

Working in partnership with the Sports Turf Research Institute (STRI Ltd), Green-tech supplied three different bioretention blends for testing:

Blend 1 is the standard Green-tree bioretention mix, featuring screened silica sand, green compost and blown clay particles. This provides sufficient permeability to avoid waterlogging, while at the same time providing enough nutrients and organic matter for the shrubs and other vegetation.

Blend 2 is Green-tree’s High Performance bioretention soil, which has been improved to allow a greater percolation rate, whilst maximising the ability to sequester pollutants from the surface runoff.

Blend 3 is an experimental custom soil containing brick fragments, that in theory should aid permeability, whilst improving filtration. It will be interesting to see how this performs against the more traditional mixes.

The performance of each bed will be monitored by Liverpool City Council, in collaboration with the University of Liverpool and The Merseyside Forest organisation.

The various testing parameters will include:

Water flow during storm events and the velocity of discharge.

Using moisture probes to monitor both moisture and temperature levels between the beds.

How the different soils affect: vegetation, pollinators, water quality (and pH levels) and air quality

Pictures courtesy of Martha Redman STRI, Juliet Staples LCC, Dan Dean Photography