P. tanacetifolia is a ‘green manure’ and is used to improve the condition of the soil. The bees love it and it grows easily from seed sown directly where it is to flower. This image shows the flowers fully open having extended over the last two to three weeks, they are about to set seed and this is the right time to chop up the plants and dig them in. After a couple of weeks the ground should be ready to plant or sow.
I have also seen P. tanacetifolia used in roadside wildflower plantings by my local council and it looks a picture.