I'd want to know what's in that "meadow" before deciding on what chemical to use to kill it. To wit, are there valuable native species present in the meadow?

Second,
I know next to nothing about production sunflower growing-for seed/oil, I presume-but there are numerous native species of sunflower that can be good additions to a native planting. I'm just not sure where you're trying to go here. Some (but not nearly all) of the native species of sunflower, at least up here, are Maximillian and the sawtooth sunflower. At least in the case of the latter, it is adapted to fairly wet conditions, and when well-sited, can form large patches, even to the extent of being somewhat thuggish. Nice plants though.

So what are you trying to do, farm sunflowers or add native sunflower species to a meadow planting?

+oM

We bought and subdivided half a farm -- 65 acres in all, with only four homes. We built on the ridge and part of our 20 acres is what I call meadow -- The farmer ran cattle on the property for 40 years before we bought it. We've been mowing the meadow areas. The wild things that I can identify ragweed, blackberries, thistle, and dock. We're not trying to grow commercially, but just to have some pretty areas to see as we drive in our lane, and to feed the local birds -- which may number in the millions, considering how fast I go through birdseed! We're leaving plenty of acreage wild, and where we don't plant, we'll continue to mow. We're planning to try three or four patches, to see what varieties do best. Our soil is not great, and there's no way to water, so the wilder the variety, the better!

I know Roundup will make it easier to plant, but the weeds you listed will always reseed and come back. I'm thinking it might harm the birds to eat tainted seeds. My friend never sprayed or weeded and her sunflowers grew better than mine did in bare ground.

Hostagrams, if you do a search on Helianthus, you will see that the world of sunflowers is wide and varied. There are native species for any area of the country. Rather than me make suggestions-and you see if that's what you want, or if it is native to your area, why not start there and break things down from that list. Without a doubt, there will be species suitable for your intent. And yes, some degree of soil prep will aid germination. Basically, these are big, tough plants, but in order for them to take hold and grow initially, at least some prep work should be done. You could use a variety of techniques so that you end up with bare mineral soil where you want to plant the seeds. This is important, as is the need to not have competing vegetation take over the area too quickly. Sunflowers as a group are more than able to hold their own, but again, the little seedlings need to be given a chance.

I know if I was doing this, I'd kill off whatever weedy vegetation was growing where I wanted my sunflowers via Roundup or its generic equivalents. When done properly, there is no carryover effect whatsoever. That information in post above is wrong. We do this all the time, and at many acres at a time, I might add. It's proven technology. Otherwise, the old cardboard smothering or similar methods will get you there too.

Finally, the sooner you can plant your seeds-realizing again that I don't know where you are-the better. Ideally,a late fall planting gets the seed just the right (tiny) distance into the ground, but if you can get out there now yet, you may be able to broadcast these seeds now. some plant seeds need to undergo a process called 'stratification', which entails a certain amount of time spent cold and moderately moist. Fall sowing is ideal, but as I said above, there are work-arounds.

+oM