In the middle of July 2020, we (Northern Virginia, Zone 7) had a prolonged period during which tomatoes would not ripen. That attracted a lot of attention, locally, because most of us had never experienced that. Questions were posed on our local plant-swap group, and the answer came back that it had been too hot for green tomatoes to ripen.
By mid-July 2020, I was so tired of looking at the same green tomatoes that I hung up some shade cloth, hoping to moderate the temperatures in my tomato patch (Post G11). Not sure that it did much, but it at least made me feel like I was doing something. Maybe it helped, maybe it didn’t.
But summer is always hot in Virginia. What made that July any different from any other Virginia July?
I tried to pin that down a bit further. After reading a bit, and plotting our weather data, the key turned out to be warm nights. If the nights consistently remain above 70 degrees, that’s too hot for the processes that tomato plants use to start their green fruit to ripen. Here are the graphs, originally discussed in Post G22-022. These are actually for Dulles Airport, about 15 miles west of where I live, and likely are a bit cooler than what I actually experienced in my garden.
Source: Calculated from historical weather data from NOAA, for Dulles International Airport.
Weather is not climate. And this one-off non-ripening event was a one-off event. But I think it’s worth noting that computer-based models of climate have long predicted that nights will warm faster than days. (And now, in fact, that’s happening — Google it.) The average differential is small, but, looking at the graph above, it doesn’t take a whole lot to push my area into the no-ripening zone for tomatoes.
This is all by way of warning for my fellow gardeners in this area. Looking at the weeks ahead (see image to the left), in Northern Virginia, we’re commencing a long stretch where temperatures are predicted to remain above 70F. For sure, there is some variation in the predictions, particularly in the further-out period. But after looking at a half-dozen long-term forecasts, the consensus is that, at best, we’re going to get one nighttime low below 70F, between now and the end of July.
The long-term forecasts seem to diverge on the 26th, with some showing a few days of nighttime temperatures under 70 (at Dulles Airport), and others not.
But even if we get a break, that unique one-off event of July 2020 doesn’t seem quite so unique any more. It makes me wonder if this is the new normal. It certainly makes me regret that I only planted my heat-tolerant tomatoes a couple of weeks ago.
What I find so odd about this is that we’re having a string of exceptionally warm nights, but the days aren’t exceptionally hot. Around here, 100F would be an exceptionally hot day, and we’d expect to see only a few such days in any year. But maximum temperatures are going nowhere near that.
So, we’ll see. A forecast isn’t reality. Maybe this (and similar) forecasts have enough upward bias that we really won’t be seeing nights consistently above 70F. But if the forecast above is correct, we’re about to have another mid-July period during which tomatoes ripen slowly, if at all, due to the high nighttime temperatures.
I’m going to ponder this for the rest of the day, and maybe take some action. Maybe not. I could bring in all the tomatoes that have started to ripen, so that they can ripen indoors, and I’ll have a clear indication of whether or not anything that’s green now has started to ripen. Maybe hang a bit of shade cloth over that part of my tomato patch.
But, really, there ain’t much you can do. I guess the real message here is that if your green tomatoes don’t ripen over the next two weeks … nothing’s wrong? Or nothing’s wrong now that hasn’t been going wrong for a long time. And likely will get wronger as time moves on.
Addendum: Picking and documenting.
Here is my patch of early-season tomatoes, the next day, after picking everything that was anywhere near ripe. I’ve circled the most obvious green tomatoes that remain on those plants. A few have just a tinge of color.
If this works out as predicted, I’ll be able to come back in two weeks and take a picture of those same green tomatoes hanging there. That’s as close as I can get to showing cause-and-effect between nighttime temperatures in excess of 70F, and no tomato ripening.
By contrast, the ripe tomatoes I just picked are going to become dried tomatoes, using a combination of a simple solar dryer (during the day) and a Nesco electric dryer (at night). These aren’t ideal tomatoes for drying — you’re supposed to use paste tomatoes, which have less liquid. And these are in chunks — halves of quarters — so they likely will take some days to dry. But I imagine they’ll taste just fine.
The dryer is just a plastic tote with a computer fan for ventilation, and a couple of screened holes for fresh air intake. Description of construction and performance is given in Post G22-015 and linked earlier posts.
