That doesn't look like drooping. It looks like epinasty, which is a turning downward of foliage. Notice how the leaves are still turgid--they're still "stiff" but just curling downward? Wilting from lack of water looks very different, i.e., leaves get thin and floppy and just hang down instead of actively turning down.

Do you keep the soil they're in constantly wet? This sort of epinasty is often a response to roots that are too wet, which causes plants to produce ethylene. Tomatoes are especially sensitive to ethylene and curl down like this in response. In enclosed conditions, you might also have a source of ethylene in your greenhouse triggering this. In fact, tomatoes are often used as the "canary in the coal mine" for ethylene in the greenhouse.

A good rule of thumb is to err on the side of too dry rather than too wet. Also, less frequency of watering is better than very frequent watering.

Don't water your plants on a schedule because no schedule can account for all the conditions that affect soil moisture and plant water needs. Instead, check the soil manually before watering. Dig down a few inches and feel the soil with your fingers. If still moist, don't water yet. If pretty dry, then water deeply and thoroughly and then don't water again until the soil a few inches down is getting dry.

Epinasty may not reverse in already affected foliage, but if the waterlogging problem is addressed and doesn't progress to fungal problems, root rot, nutritional problems, etc., the plants will be fine. Those leaves can still photosynthesize, etc., and new growth should be normal.

Thanks so much gorbelly. I have often been accused of overwatering. I will let them dry out. They do seem worse after my watering of yesterday.!! ): What might cause ethylene in a greenhouse?

I just read your link that said that heaters can produce ethylene. You know, we have had a cold snap, and I have had to heat the greenhouse at night. I will ventilate and hope for the best. Will this permanently hurt my plants? Thanks so much, I really do appreciate your help. I am going out to open the window right now....

I'm not a greenhouse grower, so I don't have a ton of information on that. But common sources are heaters, smoke, rotting vegetation, ripening fruit, etc. I imagine good ventilation is key to avoiding excessive ethylene buildup in a greenhouse and important for other reasons in greenhouse growing as well.

The most likely explanation for the epinasty in your case is overwatering, though.

Epinasty itself won't hurt your plants much. It's most troubling as a symptom of chronic wet feet in tomatoes, as the soggy roots will lead to disease and poor growth over time. When you get to a point where you don't need the heater anymore, I imagine the new growth should be normal, and the plants will be fine.

I would consult your local extension or someone you know who grows in greenhouses to see whether the levels of ethylene in your greenhouse are something to worry about. Tomatoes are very sensitive, and what causes curling in their foliage may not be troublesome to your other plants.

Thanks so much. I will let them dry out, air out, and hope for the best. I really appreciate this.

Just an update - I let the greenhouse dry and air yesterday, and in the afternoon the plants seemed so much improved. The temperature was in the 80's in the greenhouse. This morning, with no added heat the temperature was in the high 40's and the plants were a little "droopy" ( not sure what other word to use). The affected areas were a little limp, but not curling under and were much better than yesterday. I think now I now how to manage this situation and thanks so much. best Peggy

Thanks so much. I will certainly keep an eye.

My plants look great now. Just a touch of the curling left. I have not had to heat since that time that I had this problem, and I really think that that was the problem, because my watering habits have not changed, and the plants are fine now.

Great to know they're doing better!