Optimising Planting Choices for Domestic Gardens & Green Roofs

Thomas Rawson

My 6-week research placement was with both the Maths and Agriculture departments. The main goal was to develop a mathematical method by which to calculate the best combination of plant species to achieve the optimum combination of ecosystem services. For example, if one wanted to cool the air of a domestic garden, but was limited by how much they could spend on plants, what is the best they can do with the money they have?

I was provided with a large data set by Dr Tijana Blanusa containing information on a selection of garden plants. This set covered various ecosystem services and other variables such as water retention by leaves, soil temperature, cost, and plant watering requirements. I then organised this into a more concise format and focused on four plant species. I created a simple linear model that could take into account different ecosystem services. At this point I was advised and guided by Dr Danica Greetham in the construction of a variety of optimisation scenarios and seeking solutions by using the Python programming language to work directly from the data tables I had constructed.

I was able to represent graphically these solutions by showing how the optimal result would vary with respect to the initial constraint. The below picture shows the best one can possibly cool the soil of a garden depending on the amount of money available to spend on plants (from the selected four species).

It soon became apparent that this work would be very relevant to the construction of green roofs, whereby we seek to better insulate buildings by utilising plant life. Most green roofs currently consist of just Sedum, however this research project has shown that a better solution would be to use a combination of plants, the exact makeup of which would depend on resources available and the conditions of the surrounding area.

The entire experience has been an incredibly rewarding one. To be given a chance to exercise the skills I have acquired so far at university has been very enjoyable and provided a wonderful taster of the research process.

Thomas Rawson