What do you think about planting in tyres?

I have some old tyres and because I live in a dry semi-arid climate I thought maybe I would put my little golden wattle and bottlebrush tubestocks into them. But I hear the tyres leach toxic material into the soil, is this correct? They are painted with primer, on the weekend my kid and I were thinking of painting them some colours – would the paint help or worsen the potential for toxic material to contaminate the soil?

I plan on eating the bottlebrush flowers. Am I better off mulching well instead?