Tomato-Ripening Voodoo

Q: What’s the best way to get tomatoes to ripen on the vine?

A: Sing very loudly in the garden (bawdy songs are best). Soon, you’ll see them start to blush.

OK, what can we really do to get our tomatoes to ripen? Well, it would seem—as the old joke hints—not much.

It turns out, tomato ripening is all about the one thing we outdoor gardeners can’t control: the weather—yes, the very temperature of the air.

But it’s not exactly the story I would have expected for a crop so often described as a heat-lover: Numerous online extension reports and bulletins say the optimum temperature range for ripening tomatoes is 68°F to 77°F.

That’s lower than I thought! (And now I know what to wish for!)

"The further temperatures stray from the optimum, the slower the ripening process will be," says Rosie Lerner, a consumer horticulturist with the Purdue University extension. "And, when temperatures are outside the optimum range for extended periods, conditions may become so stressful that the ripening process virtually halts."

(Look around online and you'll see nearly this exact language parroted from extension to extension. A North Carolina State University article regarding commercial tomatoes puts the optimum ripening range even lower, at 65°F to 70°F.)

Lerner goes on: "Tomatoes do not produce lycopene and carotene, the pigments responsible for ripe tomato color, when temperatures are above 85°F. So, extended periods of extreme heat cause tomatoes to stop ripening."

Indeed, according to this Colorado extension bulletin, tomatoes aren't so much heat lovers as they are terribly cold-intolerant, especially in chilly springs: "Tomatoes grow best at uniformly moderate temperatures between 65°F to 85°F."

I needn't yearn for 90-degree hot days to ripen my tomatoes any more, apparently.

But … I won't be singing to my fruit either.

As a longtime tomato-obsessed gardener, I use the following four tricks instead. Do they work? I can only report, anecdotally, that I always had ripe tomatoes by September in Seattle when I lived in Seattle (not the easiest climate for tomatoes). And things seem to be on track in my Minneapolis garden this year, too, despite a late start.

1: To boost success and reduce disappointment—and waiting—I mostly grow cherry tomatoes such as Sun Gold (above, my first of the season), Sweet Million, Indigo Rose (below). (I leave the slicers to the farmers market vendors.)

2: I lay down red plastic mulch. Developed jointly by the USDA and Clemson University in South Carolina, this wispy plastic-bag like material "reflects far-red light wavelengths" and "helps tomato plants grow faster and produce more abundant crops."

I am not sure it if it aids ripening, but I've used it for about 10 years and it at least inhibits weeds and helps retain soil moisture. Online reviews are quite positive, too.

I place old ceramic tiles around the edges to keep the so-called mulch from blowing away. Tiles, like stones, reflect light and lasting warmth, a bonus in Minneapolis, where we don't regularly see daytime temps over 90°F anyway and our nights often dip below 65°F.

3: I remove late-season blossoms and newly formed fruit. By the time we reach late August, it's unlikely that immature flowers and fruit will deliver edible tomatoes. I hate to kill babies of any sort, but this reportedly focuses plants on mature fruit. More important, perhaps, it keeps plants from taking over the yard and it increases air circulation. (Note: All season long, I remove or tie back foliage that threatens to touch the soil. This prevents the spread of disease or late blight.)

4. I reduce watering to about once a week, if that in August and especially September, not allowing the plants to wilt, but not indulging them like I do earlier in the year either. This classic Pacific Northwest advice might be derived from old wives tales—like so much of gardening advice—but as a hard-core overwaterer, I happily adhere to it. (I'm too tired to water in September anyway!)

What voodoo do you do to turn so-many green orbs into bursts of red delight?