It is now time for the fourth and final phase of my 2022 tomato strategy, heat-tolerant tomatoes.
I outlined the overall approach in Post G21-001. There, among other things, I listed the varieties I’m planting. To recap, the goal is a continuous supply of tomatoes all summer long, with a large batch of paste tomatoes for producing dried tomatoes.
I have an additional goal of minimal effort. So, no staking (a.k.a., the sprawl method of tomato cultivation, Post G22-018). No spraying — if they die, they die. And minimal pruning — just enough to keep them confined to their garden beds.
Slacking off this year is my informal test of whether or not the additional yield from careful cultivation is worth the additional effort. I suspect that a lot of the more labor-intensive gardening approaches you read about are for people with space constraints, trying to maximize production within a small garden area. I don’t have that problem, so maybe I’ve been putting in a lot of extra labor for no good reason. If I can keep myself supplied with tomatoes, with a low-effort approach using more tomato plants, that’s the way I’ll go from now on.
I have planted:
- Some early-season/cold-tolerant tomatoes, planted in early spring. These have all been setting fruit for weeks. From the looks of it, I ought to begin harvesting ripe, golf-ball-sized tomatoes in the next couple of weeks. These should be small plants, and I’m growing them in standard tomato cages.
- A large number of paste tomatoes. These were partially mown down by deer. Most seem to have recovered. I replanted those that didn’t and added another bed of them. I’m growing these on woven black plastic, no staking, no cages. They’ll just grow where they grow.
- A handful of heirloom varieties with reputation for excellent taste. I started these soon after the paste tomatoes, but these should take longer to ripen. These are being grown over traditional (e.g., straw) mulch, no staking, no cages.
So far, these have all satisfied the #1 criterion for garden plants, failure to die. Even most of the ones that were munched by the deer have come back. That said, the early-season and high-taste-heirloom tomatoes are already showing signs of leaf diseases. I am doing absolutely nothing about that, other than cutting off and discarding the occasional yellowed leaf.
Tomato strategy, Part 4: The summer 2020 experience.
Everybody knows that tomatoes can’t tolerate frost and don’t like the cold.
But most tomato varieties don’t like excessively hot weather either. As a consequence, if you live a warm climate, your tomatoes may take an extended late-summer vacation. Little new fruit will be set, and existing fruit will take a long time to ripen. Both of which will continue until temperatures fall.
That lack-of-ripening happened around here in 2020, and it seems to have caught a lot of people in this area by surprise, me included. The only solution available appeared to be to shade your tomato plants to keep the peak temperatures down (Post #G12, July 21 2020). That appears to work, some.
Apparently that’s a well-know technique in very hot parts of the country (e.g., Texas). But it’s definitely a novelty around here (Zone 7, Virginia).
And that’s kind of odd, because, on the face of it, Virginia ought to be plenty hot enough to prevent tomatoes ripening in most summers. And yet, that seems to be a rare enough occurrence that it caught a lot of people by surprise.
The normal explanation of tomato ripening and temperatures is that production of key ripening chemicals in tomatoes begins to slow or stop at high temperatures. Depending on the source, tomato ripening stops entirely at 85F or 90F, and ripening slows above roughly 75F. These are not unusual daytime temperatures in Virginia in the summer. If that’s the whole story, how do we ever manage to get ripe tomatoes around here?
In contrast to 2020, when there was an extended period where tomatoes did not ripen, I had no problems in 2021. That was, in fact, my best-ever year for tomatoes.
Here’s where it gets odd: That contrast is all about nighttime lows. Comparing my local weather data for 2020 and 2021 (June to September), daytime peak temperatures were not all that different. No surprise, summer days are hot here in Virginia. That’s the top graph below.
Source: Calculated from historical weather data from NOAA, for Dulles International Airport.
What does appear to be different about 2020, however, is a long string of nights when temperatures stayed above 70F. (These data are from an airport about 15 miles west of here, and likely some small urban heat island effect keeps my temperatures a bit higher than what is shown on the graph).
And, if I look hard enough, I can find hints that it’s the combination of warm days and warm nights that leads to total inhibition of tomato ripening. The U. of Minnesota extension service says this:
Once we start to get some cooler nights, tomatoes will again have some hours in their ideal ripening temperature range, allowing for tomatoes to fully ripen and redden.
Assuming that’s accurate, that seems to fill in the picture for why we had a stretch of non-ripening tomatoes in 2020. Hot days are normal around here. What put the tomatoes on hold was a prolonged period of hot nights, in addition to those hot days. Best guess, if there’s any significant time period in which temperatures fall into that ideal-ripening zone, tomatoes will ripen. It’s only when temperatures stay too high around-the-clock that ripening totally ceases.
Tomato strategy, Part 4: Heat-tolerant tomatoes.
Returning to the present, even if ripening does not cease, hot weather slows down tomato production considerably. To a close approximation, new fruit isn’t set, or sets a low rate. In addition, most sources agree that excessive heat leads to inferior fruit.
But some tomato varieties are more heat-tolerant than others. At least, by reputation. Google it, and you’ll see a lot of recommendations for heat-tolerant tomatoes. You’ll often see the same set of recommendations, which I suspect comes not from original observation, but from people effectively re-posting existing lists.
That said, this Mother Earth News article is a good introduction, with references to some more formal research on this issue. University of Alabama extension service provides estimates of 72F nighttime and 85F daytime as the upper limit where most tomatoes will set fruit. Extended periods with temperatures exceeding that will generally result in no fruit set in most tomato varieties.
The upshot is that I started some seeds for two varieties of heat-set tomatoes today. That’s Arkansas Traveler and Floradade. If they stick to the schedule, they’ll be flowering and setting fruit from mid-July forward, which is when most of my other varieties will be stressed from the heat. With any luck, these will pick up the slack in overall tomato production during that period.
