The quality of imported topsoil used on a project very often comes down to a project's Topsoil Specification. It details what should and should not be in the topsoil. The topsoil specification therefore needs to include the technical elements that will ensure an effective growing medium is provided.
The most functional specifications are those that list which properties the topsoil should possess prior to turfing, planting or seeding. These normally include:
- Visual examination - soil structure, consistency, foreign matter, etc.
- Particle size analysis (texture) and stone content
- pH and salinity values
- Major plant nutrients
- Organic matter content
- Potential contaminants (e.g. heavy metals, hydrocarbons, cyanide, phenols)
The values set against each property will vary depending on the required performance of the topsoil. There is a tendency to use the same specification for every landscape project regardless of climate, plant species, programme or construction constraints. Usually some modification to a 'template specification' is required for each project and often it is appropriate to have more than one specification if a variety of different 'landscape habitats' are to be established e.g. tree pits and wildflower grassland.
Once you have issued a specification, stick to it and do not be persuaded to change it on price alone.