The words "heat", and "cold" mean different things to different people. When I lived in the PNW, people were dropping in the streets when the temp cracked 90F. Down here, anything below 90F on a summer afternoon is a cold wave. Hands in pockets, etc. So I could imagine that these varieties had some value for people living in Chicago or Bangor. That's correct that "heat tolerant tomatoes" used to be a bigger deal than it is today. I think that language used to have some marketing value, before folks figured it out.

Memories Dan; I used to live in southwest Virginia. The mayor of Bluefield use to ( maybe still does) set up lemonade stands on the main drag and hand out free lemonade whenever the temp cracked 90. Here 90 is a hot day only when it occurs in January.

Given the propensity of "heat tolerant" tomatoes that really don't make the grade, I wonder if it would be more instructive to publish lists of "heat INtolerant tomatoes". As in, if you live in the south, don't dare plant these!

I'm not sure, but I think it's the night time temps that matter. Not sure where I read this (perhaps a seed catalog) - but tomatoes will only fruit if night time temps are less than 75. Does anyone know for sure?

I've heard that too. Now, I'm not sure that a tomato flower can tell the difference between day and night, but I suspect the issue is the highest temperature for effective pollination, and the lowest temperature is always going to be at night.

I believe that high temperatures make the pollen sticky and
non-violable. The question is whether low temperatures can undo that
stickiness. If the daytime temperatures are high enough to actually permanently damage the pollen, low nighttime temps are not going to lead to any fertilization.

Heat tolerance is fine, and it's not the heat, persay, that I'm worried about, but it's bug and disease tolerance that's the real problem here.

I think there's something to the nighttime temperature theory. Here, 90+ daytime temperature is very common July-October (100+ is not uncommon, here and there). However, we normally have relatively cool nighttime temperatures (50-60-70ish), even during the hot months. I haven't noticed that much of a slowdown in production during the hot months - there will be some but no complete shutdown. Also wondering if "dry heat" vs humidity makes a difference?

High humidity is the bane of tomatoes (and other vegetables) as fungal diseases run rampant.

Humsi, that's a good observation. I suspect what that means is that it's not the high daytime temperatures that prevent pollination. Rather it's the lack of any temperatures below 75F that do it. So nighttime temps are probably indeed the deciding factor. Also of interest is that to the extent that daytime high temperatures mess up the pollen, they recover their viability at low temperatures.

Of course, in many climates, including mine, nighttime temps just drop down to the dew point, at which point the humidity is 100%.

Certainly when it comes to pollen stickiness, high humidity makes it worse. That's well understood.

If this is all true, I wish garden writers would get this straight. Of course, much gardening journalism today is just viral, where someone says one thing so everyone else does too. Not a lot of independent thinking out there.

I contend with 100 degree plus days most of the summer. It is a dry climate though so I don’t have to contend with the fungal diseases. To combat this and get good yields I’ve come up with a few keys.
Plant where they get afternoon shade
Drip system
3” or more of mulch
Also I plant a lot of early varieties as early as I can and it seems like most cherry tomato varieties still produce in the high heat.

Well, shade, mulch, and irrigation won't affect the air temperature, and it's the air temperature that we're talking about here. What are your evening temps like?

Another thing I do is go for an early summer crop and an October crop.

I don't mean to change the subject but I have a question and can't figure out how to post on this group anymore it has changed. Has anyone here heard of a tomato called 'Polish Nights' ? Apparently it is a black type tomato from Poland or some place like that. Pictures show seedlings have a leaf shaped much like a bell pepper leaf. The tomatoes are colored much like Cherokee Chocolate.

I don't think shade is to be ignored. A shade cloth even with high temps could make the difference. In the south of my country people grow tomatoes all summer at temps that often go often above 100c and very warm nights (in greenhouses with 40-50% shade cloth). It's an extra stress, also the plants will lose serious amount of water in full sun. They also mostly use hybrids.

Good point. I know some people who have to use shade cloth due to too much sun and heat. I even heard one Italian gentleman claim that where he is from in Italy, tomatoes are considered a shade plant due to the extreme summer climate there.

A few places advise 50% shade cloth to encourage pollination in high heat, and make the interesting point that pollination tends to occur between 10am and 2pm. Never heard that before. Can that be right? To the extent tomato pollination is induced by shaking blossoms, and to the extent that it's usually more breezy in the daytime than at night, I guess there might be something to that.

But I have a bed that doesn't start to get sun until 12:30pm, and my tomatoes there don't fruit any later than in a full-sun bed. Also, I'm not aware that the latest tomatoes I get tend to be in shady parts of the plant.

It is true that sunlight on the blossoms will make temperature on the blossoms higher than air temperature, but ...

If there were such slicing size tomatoe,it might corner the market in Texas(I'd buy it). Cherry size always produce's farther into summer than others. Were it not for the fact that decent tasting tomatoes won't ship,some entrepreneur could ship toms North in early season and South later on. One without ethics could heavly market a plant or seed purported to produce through July,August and September then skip town before folks realized they were scammed. There have been millions of "cottonless"cottonwood seedlings sold that rained tons of cotton when mature.

I'm sure there are decent-tasting oxhearts that would work for shipping.

Heat-tolerant tomatoes don't necessarily produce a lot of tomatoes in the heat—they just can produce any at all. Most of the heat-tolerant tomatoes I've tried will produce a few fruits when the weather is between 90° F. And 116° F. in my area (with cooler nights than average and semi-arid air), but there are only a few I've found that are prolific in the heat. Sweet Orange Cherry, Galapagos Island (my version of it), Early Girl F1, Chocolate Pear, Husky Cherry Red F1, Pink Berkeley Tie Dye, and Matina are some of those that have produced the most in the heat for me. Historically, though, stuff that does well in Texas doesn't seem to do that well here and vice versa.

You might try Pruden's Purple and Creole in Texas and see how they do. They're not small. Creole could ship well (not PP, though).

Sweet Ozark Orange is a good one that might actually do decently in Texas (I think I've read a favorable review from a Texan), and it does well here. It's very firm if you don't let it ripen too much (but it can get pretty soft if you do). It's too late for me to be able to say how heat-tolerant it is, but one of its parents is supposed to be heat-tolerant.