I can't tell exactly what the cause is, but here are some suggestions that may help:

Cut early in the morning.
Cut before flowers are fully open (you can cut as early as when the buds are just showing color, but the earlier you cut, the smaller the flowers will be).
Cut into water that is no warmer than ambient temperature.
Keep the plants well watered.
Use a cut-flower preservative.
Keep cut flowers in a cool place, out of the sun.
Don't put cut flowers in with any other cut stems that ooze a milky white fluid (milkweeds and spurges are especially bad).

Lots of people have trouble with Moulin Rouge and Strawberry Blonde drooping and dropping petals. I found I didn't, as long as I cut them before they are fully open.
Failing everything else, find out what's in your water - water pH and various chemicals can have a dramatic effect.
DON'T use softened water.

Forgive me if you already know all that stuff. It was everything I could think of that can cause drooping.

Jeanne

Susan,
The answer to your question is right there in your first sentence. You've planted your sunflowers in poor soil and they haven't received enough water. Sunflowers are H.E.A.V.Y feeders. They require heavy doses of nitrogen and lots and lots of water. Feeding and watering at the critical stages of development is crucial to having marketable sunflowers that your customers will come back to purchase week after week. We don't have to say how long our sunflowers last. Our customers tell us; and, they tell the person standing next to them at our table at market.

Cutting early in the morning is humorous to those of us professional growers who cut all day long. Actually, sunflowers don't really care what time of day you cut them. Sometimes we take our utility van out to the field, and cut sunflowers and stack them dry in the van. We bring them up to the barn and put them into plain water. Research has found they do best in just plain water.

This statement is incorrect: 'Cut before flowers are fully open (you can cut as early as when the buds are just showing color, but the earlier you cut, the smaller the flowers will be). The size of the flower is determined long before it is ready for harvest. You cannot cut the sunflower when the buds are just showing color. You have to wait until a couple of the petals are just starting to lift off the disk. We try to catch them at this stage; however, we also cut when the sunflower is fully open.

We grow thousands of sunflowers each season; and, we have alot of competition at market. Our prices are actually higher than the competition. We usually sell out. The competition usually does not. We have a reputation for having the best cutflowers on the market.

Trish

I've harvested them at any time of day also. I just figured they'd do better harvested cool and well hydrated. Trish, you've probably hit the nail right on the head, those plants are probably undernourished and underwatered and therefore stressed before cutting.

Cutting them as early as when the buds are just showing color is something I've learned FROM EXPERIENCE, not from a book or anybody else, although I think I got the original idea from a book or I probably wouldn't have tried it. I've cut them as buds just showing color, many times, into my homemade preservative, and kept them in my house, for various reasons. They always open, within a day or two to as long as a week and a half after cutting, if I cut them VERY young. The size they reach is directly proportional to how young I cut them. Customers I've sold them to have always related the same experience in their houses. Of course the size of the flower is genetically determined, given the correct amount of water and food. With insufficient food, they don't get as big. I've found that to be the case whenever I've planted them in poor ground or haven't watered enough, even if I don't cut them at all. My theory is that cutting when still in bud form deprives the flower of the best light and the best food - no preservative of any sort is the same thing - so although it blooms, it can't reach its predetermined size. In plain water, I can only suppose they would be even smaller or wouldn't open, with no nourishment whatsoever, but I never tried it in plain water. My theory doesn't matter, though, what matters is that it works. It does. I've used it just for myself or for customers who wanted a bouquet that would be at its peak not now, but in a week, or even further out. My house generally doesn't get warmer than 74 degrees or so; I surmise that that helps. Of course, if you want your flowers to be perfect the next day, they should be farther along, with at least a couple of petals lifting, as Trish described. I always tried to put a few buds in each sunflower bouquet as a surprise for later.

Trish, have you ever tried it? With preservative?

Jeanne

Boy, was that question I asked at the end of my last post ever dumb! If you had tried it, you'd already know it works, and that the flowers don't reach full size!

Jeanne

Thanks Jeanne and Trish,
Yes, I was afraid of that. I should have found room for them in my home garden. Will do so next year! All my flowers grew poorly last year, I thought it was due to lack of rain. Now I think it is the soil- even my bulbs that like sandy soil are 1/2 the size the ones at home are. And yet the farmer seems to have no trouble with his vegetables and raspberries!
Trish, I can't even imagine being on the scale that you grow at. Do you employ workers?