I grow both hybrids and open pollinated (some of which are considered heirlooms).

Most any tomato will crack if given too much water by irrigation or rain but some are less prone then others. Most hybrids won't get concentric cracking but they can still get radial cracking from the stem end. Some open pollinated that have been less prone to cracking for me this year are Rebel Yell, Orange Jazz, and Girl Girl's Weird Thing.

Picking at first blush can diminish the cracking substantially.

I'm really not sure if cracking is a heirloom issue at all. Sweet 100 is a hybrid cherry, and the others are OP full size. Cherries are less likely to crack. Large tomatoes are more likely to crack. I mean, hybrids are really just crosses between what you call heirlooms. Do you have any better evidence that your cracking problem is due to tomatoes being heirlooms? As to keeping full sized tomatoes from cracking, Lone Jack has good suggestions.

"Do you have any better evidence that your cracking problem is due to tomatoes being heirlooms?"

No. I just thought that due to the thinner skins (of the ones I have, anyway) and non-uniformity of shape, they would be more prone to cracking.

But again, I don't think thinness of skin or non-round shape is a property of an heirloom/OP tomato. You might want to start selecting thicker skinned and round tomatoes, and not worry about whether they are heirloom/OP. That is, you may just have evidence that thin skinned and non-round tomatoes are more prone to cracking.

Hybrids can be bred for numerous traits...production, heat tolerance, disease resistance, uniformity, or even resistance to cracking.

I like a mix of OPs and hybrids, and cracking is a concern in my area. Supersonic (VF) is popular locally for that reason. But on the OP side, there is a variety called Ruth's Perfect that you should try before giving up.

I try a different variety or two every year but my mainstays are Sudduth pink BW and Cherokee Purple. I tried Cherokee Chocolate this year and saved the seeds, it was pretty good. I have yet to find a hybrid that fills my salad bowl with juice, they all seem a bit more mealy textured than the heirlooms.

As for them cracking, yep, not nice, but for me it only occurs when it rains as the tomatoes are near ripening on the vine. Timing is of the essence to get them picked just before or just after a rain hits. It's also helps to pick them before watering the plants even if they just have a hint of turning ripe. If they're picked at least half ripe they ripen indoors a-ok. Happy Harvest

Agree with the others who have pointed out that cracking isn't relevant to choice between heirloom or hybrid nor to thin skins or not.

They can all crack if water and drainage aren't well managed and/or if they are left on the vine too long. Preventing cracking is one of the primary reasons so many recommend picking at color break and finish ripening inside.

So make your decision on more relevant issues like flavor (the primary criteria for many), disease resistance, amount of production, etc.

Dave

Note that "cracking", which is usually the term for a little self-sealing perforated slice around the stem, is common in many tomatoes. They just do that. No big deal. "Splitting" is when you get a big slice down the side, and poor water management is usually to blame. Fruit rot results. Note that container-grown tomatoes are harder to manage water in, and may be more prone to showing splitting. Splitting is something that happens when the soil is drenched, like with a mammoth rainstorm OR poor drainage in a container.

I raise 1 heirloom...Suddeth Strain of Brandywine...Fedco has a select strain of that one. Mostly I raise hybrids for...yes, less cracking. Try Gurney Girl Best for an explosion of non crackers.

<Well, I didn't realize the cracking was primarily a water issue, so thanks all for educating me on that!>

IME cracking/splitting can happen when there is an increase in water available to the plant, esp. during a hot, dry growing period.

Think back to your watering schedule/routine to figure if the plants were suddenly getting an increase in water from a rain storm.

If that's not it then picking early may be of help.