While sprayed chemicals would be bad too, we are also worried about the systemic pesticides that are typically used in store bought plants. These plants are grown in treated soil and the pesticides are taken up into the plants tissues to protect them from insect attack and keep the plants looking pretty and healthy for market. These systemic pesticides can last a year in the plant's tissues. Be careful. Many sellers of plants don't even know about this. I've had a few of them call their suppliers and get a nasty surprise.I was washing it for too long because of that worry of the cars. I then stupidly realised that there us more growing un my back garden with more choices aswell. I'd been pulling up the best choices when gardening, So now I've got a pot especially for weeds and clover to grow in. Plus pansies that I've specially ordered that I 100% know they havnt had chemicals sprayed on them.