As long as ya got that stack in the garden, might as well use them to grow ya some 'taters in next spring Paul. Start with one, fill it up with dirt and some seed 'taters. When the sprouts get up 8 inches or so, throw another tire on and fill it with dirt. Keep repeating till yer out of tires.
Wait until fall then just kick the stack over and you'll have more 'taters than ya can swing a cat at.