This area is intermediate desert, half a mile (about one klick) up, nearly frost free and very dry. We have either one or two growing seasons, depending on how you look at it. Temperatures in mid-summer that go into and stay in the forty degree range cause that. Toms that start in the chilly winter and those that start in mid-summer both grow like weeds and, with shading, escape wilting for the most part, but mid-summer stops most new fruiting on everything. Those that I layer or try to carry over, hoping they will recover in the cooler autumn temps, donâÂÂt do anywhere near as well as fresh plants. I havenâÂÂt found any plants yet that escape the high heat and come up smiling. The cherry toms seem to be best at that, but youâÂÂre asking about slicers. Of the ones you mention, the krim seems to get good talk.

We are still picking ripening tomatoes now in mid-December and have also started seeds for planting out in February, so itâÂÂs a constant cycle with a few months twice a year without toms to eat. I havenâÂÂt been able to get those varieties that claim to be heat tolerant to work as well as super-early determinant types but that may just be technique and location. Pollen death seems to be inescapable.

EDIT:
P.S. Seed age is never a problem if they sprout!

This post was edited by grubby_me on Mon, Dec 8, 14 at 17:22

I agree that in the dead heat of summer it is hard to get tomatoes to do their thing. Growing early and late is the way to go. I have never used shade cloth but many have and say it helps.
I routinely sprout tomato seeds a good bit older than 5 years. If they seem reluctant, then I soak them overnight in water, sometimes with a tiny drop for fertilizer.

Thanks for the reassurance about the seeds' viability. And I've missed early planting now, but I'll try anyway, and also do a late planting at summer's end.

Any ideas on the varieties I mentioned having?

Temperature stops fruit set and ripening if it gets too high, so you have to avoid the temps somehow.

My successful tomatoes have been tiny (Matt's Wild Cherry) or varieties from India (heirloom from one the SO's co-workers from India) or found thriving in Baja California.

One technique that works is to use short-season varieties developed for far north to get in the harvest before it turns hot, or for late-summer planting and an early fall harvest.

Another is to accept that the plants will sulk all summer with little activity and set fruit when it cools off in the autumn.