We changed the plastic that was on the tires to horticultural cloth. It doesn't get as warm as the plastic, as it lets air circulate, and water through. We still have to take the covers off when we water - which is every day now.
The second radish (road rash) crop is up, with the first rapidly dissapearing. Today we are waiting for a couple of truck loads of sand to spread over the clay to start getting the "big garden" going. If we can get it planted by June we should be ok. I might still use the tire method in the garden. Just use one tire, right on the garden soil, and keep it covered while the cuttings start. The tires really help keep the heat in. We will use row covers for the cabbages and turnips.
On a 'nother topic. I think my dog may have a drinking problem. She's starting to think the world revolves around her and the other day we found her in a stupor among the tires: