posted 14 years ago
I used to grow pumpkins (among other things) for a living. that includes C. pepo, C. moschata, and C. maxima. usually about fifteen acres each year. we started planting a few sunflowers in the pumpkin fields more for eye candy than anything else. it ended up improving the growth of the pumpkins.
during the middle of the day, the pumpkin leaves would always wilt, even if there was plenty of moisture in the dirt. we looked into it, and it turns out that the Cucurbita genus suffers from photosaturation. that is to say, if there's too much light hitting the leaves, they can't really take it and sort of shut down until the sun isn't so direct. so during the middle four or five hours of the day, they weren't photosynthesizing or growing at all.
when we added the sunflowers, though, they provided just a little bit of shade for the pumpkins. it was just enough to keep the pumpkins going strong right through the day without the wilting. so though they were getting less sun, they actually grew more. there weren't a lot of sunflowers. maybe one sunflower to five to ten pumpkin plants. and these were the big sunflowers.
so, I won't argue that sunflowers don't exude allelopathic substances, but in some cases they're still a good idea.
on the other hand, there's no reason it had to be sunflowers in with the pumpkins. they looked good, and folks liked them, and they're easy to grow. corn probably works just as well or better and is probably an easier crop for most folks to use. many other plants could fill the same role with different useful products.