I think your're fine with reusing your container mix. -20C would even kill late blight spores.

I never considered powdery mildew to be particularly threatening (the baking soda, canola oil spray I made kept it at bay). Thanks for the advice. I was concerned with the somewhat mild temperatures "something bad" would have already colonized the soil, didn't appear to affect anything, and then would spring out with full strength at the beginning of the year.

@daninthedirt,

Do you find that you need to amend the soil any differently when you grow only tomatoes there for multiple years, or is it the same process you'd do anyway?

I just amend with compost every year. If the tomatoes are sucking anything special out of my soil, the compost is putting it back, or I have loads of it to begin with. I had a soil test done on that bed that year, and it was full of everything.

You can make arbitrary 2-year rules like that if you presume that disease follows your tomatoes around. Doesn't seem to do that for me.

Thanks for the information. :) How much do you usually like to add?

There is a bit of a disconnect going on here :-) You are talking about containers and comments are addressing inground growing - the two are completely different situations!!

I would support the contention that you do not need to switch out the soil mix just as a disease prevention precaution. But container soil does not last forever and some prepackaged mixes barely last a full growing season!! The soil mix collapses and compresses with the need for frequent irrigation and breaks down into smaller and smaller particle sizes that impede drainage and reduce aeration. This not a concern when growing in the ground. So the recommendations ARE to replace the soil mix annually. If that is impractical, then you need to add to it with something that is more textural or durable - bark fines or perlite - in a 50% volume. Not compost!! Compost has no place in a container because it is excessively moisture retentive, breaks down too rapidly and therefore contributes to poor drainage......which may be the cause for many container plant disease problems.

Good that someone here is reading carefully! Yes, for in-ground tomatoes, no need for moving. But for containers, life is a little different. It's not that nutrients are used up (which, for containers, you're adding anyway), but that the soil structure in containers degrades. I will mildly disagree about compost in containers. Works for me as a minor constituent, but should certainly not dominate the mix.

Update:

Well, I have aphid eggs in my soil. They've come out and colonized my pea crop (which is still indoors until the freezing stops). Disappointing but not tomato specific.

I've never understood this 'soil compaction' argument, at the end of the season the medium was 'as high' up the side of the container as it was at the beginning, and it didn't have large gaps around the edges. Drainage was still very good, and the low-water usage plants I had (hot peppers) still needed watering once a week or so, if not less. I might start a new topic on that.

funkyhat

I do not know much about bugs, but read some about aphids - IIRC they do not lay eggs in soil. I do not have lots of info, but here are some of my notes:

..." Aphid sexuality is quite complex, including both asexual reproduction concluding with live birth and sexual reproduction concluding with egg laying. In spring, when hatching occurs, all emerging aphids are female and reproduce asexually, essentially giving birth to three or more clones of themselves every day. As the end of summer approaches, the reproductive strategy of aphids in climates with cold winters shifts and both males and females are produced. After mating, the sexually reproductive females deposit eggs in the protective crevices of plants; safe from harsh winter weather, these eggs hatch the following spring and the cycle begins anew...

...Each of the many aphid species has its own life cycle, but there are some features uniting nearly all of them. One feature most species share is that they are incredibly prolific. Wingless adult female aphids can produce 50 to 100 offspring. A newly born aphid becomes a reproducing adult within about a week and then can produce up to 5 offspring per day for up to 30 days.

An even more amazing feature of life cycles of most aphid species is that reproduction during at least part of its life cycle can be accomplished without the help of male aphids! Babies have no fathers.Young are born from females without the benefit of sexual reproduction, in a process known technically as parthenogenesis. When mother aphids reproduce parthenogenetically, instead of laying eggs they give birth directly to smaller editions of themselves"...

If you are sure there are eggs in the soil, perhaps they are different pest.

They're aphids.