Toss them all on the pile, root and all.

I have read something about spent tomato plants, that you have to be careful if it has bligh(?). I don't have tomato plants so I cannot say from experience.
Have to wait for more experienced people to chip in.

You can compost that used potting soil, and if your tomatoes showed any sighs of either early or late blight that soil and any plant residue needs to be composted. The disease pathogens of both blights need plant tissue (any of the "Solanaceae" family of plants) to survive and if you compost them and get the temperatue of the compost into the 135 to 150 degree range that will kill the disease pathogens.

kimmsr, if they need plant tissue to survive, how do they survive through the winter? Or in a bed that I haven't grown tomatoes in for two years. I'm really asking because I have bad blight problems that get worse year after year.

Back on topic: I sift out my used potting soil through chicken wire and store it in a bin in the garage. In spring I add 30-50% by volume sifted compost and it's ready to go for a new summer of pots. BUT I don't grow tomatoes in it so I can't say how that would work in terms of blight. But you can certainly throw the entire thing into your compost pile. Me, I would chop up the plant stem, and break up the root ball with a shovel.

IME, the mineral component of "soil" doesn't compost per se. Are these containers filled with mineral soil or more of a potting mixture (peat, bark fines etc etc.)?

I get these rootball and plant stuff all the time but for the most part there isn't a lot of true soil in them. Lottsa peat and other stuff but not a lot of soil. In any event, it all goes into the windrow and it's usually gone by the following year.

Lloyd

Thanks everyone! It isn't a lot of soil but I just hate tossing it and starting all over. So should I just set up a large bin of the soil/roots and toss it every now and then? We do vermicomposting but I could start something else outside as well. Even if I could save 1/2 and mix it with new soil I would be happy. LLoyd, it is potting mixture. Also, for future years, what is the best way to go about this? $ isn't an issue (although it is always an issue!) as much as I hate throwing it out.

toxcrusadr, this from Cornell can help explain what you want to know.

Here is a link that might be useful: About Late Blight

Thanks kimmsr!

I've been saving and reusing my potting soil for 15 years. I keep it in a cardboard lined hardware cloth bin. I amend it heavily with compost (and seaweed) from year to year, and I've had to occasionally buy new potting soil as I expanded my container gardening.

I kept the same soil in my Garlic Chive pot, not even mixing it or adding anything to it & they sprung right back to life, quite green & healthy looking, with just a few days worth of waterings earlier this year. I'm going to do the same thing with them for next year to see how long this soil will last with them, especially since i'm not sure how easy it would be to pull & repot the chives.