Please be on the look out for an invasive plant that’s flowering at the moment, called Red Valerian, or Centranthus ruber(sometimes the flowers are white). It sets seed very quickly and the seeds are wind-dispersed so they spread like wildfire. It has been a problem on some of the slopes of the mountains on the Peninsula for a few years, and now I see it appearing in people’s gardens in this area.
The plant can be pulled out if small, but when mature the roots can be as big as a bunch of carrots, and then pulling tends to just break the stem off. If it can’t be dug out, a herbicide has to be applied. At the very least, remove the flowers as soon as possible and dispose of them in a plastic bag with your domestic refuse, or burn them after your next braai. The roots are capable of cracking walls over time.
See these links for full details –
http://www.capetown.gov.za/en/EnvironmentalResourceManagement/publications/Documents/Enviroworks_Jun12.pdf
http://www.capetowninvasives.org.za/edrr/target-list
