I know that annual cornflowers are easy to grow, but as an experiment a few weeks ago I sowed half the seeds into normal MPC and half into a 50/50 mix with perite. The seeds have been in a cold greenhouse since. Today I removed some seedlings to give the others room to grow and it was very obvious that the ones grown in the perlite mix had a much better root system.
Left of center Off of the strip
In the outskirts In the fringes In the corner