Sunflowers are probably the easiest and most commonly available native plant in North America. This year I'm once again participating in The Great Sunflower Project and I've just planted the seeds they sent. Of course I'm not one do anything simple, so along with the annual variety of Lemon Queen they sent, I've also planted a few others. "Annual variety" is in bold because there's also a perennial variety that turns more into a bush.
Mammoth Sunflowers are the tallest variety I've planted. The seed packet says it gets 12 feet tall, online sources say 8 to 10 feet tall, from experience though I can say 6 to 8 feet is more accurate. That's not to say they don't get 12 feet tall somewhere but I've never had it happen here. These were planted in the back. The seeds are edible too! Not just by gold finches, you can eat the seeds. Any sunflower that has white stripes on the seeds are meant for eating. The smaller black seeds are meant for oil production but birds love them all the same. You get a lot of seeds in these packets.
Great American Giant Hybrid is the second one planted. The seed packet says 8 feet tall but online sources tell me 16 feet. I grew these last year and they were about 6. I planted these infront of the Mammoth Sunflowers but did so in a fan effect, not a row. This way if they do get big they're not blocking the view of the other variety behind them. Not a whole lot of seeds in this packet but still enough to plant a bunch.
Lemon Queen was the last variety of sunflowers and went right in the front. This will make them easy to see for the study and I have a nice big oak tree to plant a chair and watch. They get 5 to 6 feet tall, have a wonderful yellow flower.
Mexican Sunflowers, though not native and not in the same genus, are very pretty. I'm not planting them this year but I was amazed by them last year. A tiny seed to an annual plant (dies after a year) somehow turns into a 4 x 4 or 6 x 6 bush loaded with wonderful flowers that are the most intense Orange color I've ever seen in a plant. Gold Finches don't eat the seeds to this one, but I have found caterpillars eating the flowers. Don't worry though because they have tons plenty of flowers.
If I had the space to continue planting in this garden a row of Zinnias would have gone down followed by either Coreopsis, Cosmos, and or Marigolds. I believe these are all good companion annuals. Coreopsis attract beneficial insects. Cosmos are good for pollinators. Marigolds don't do much besides get eaten by rabbits. I have never see bees on them, nor butterflies or hummingbirds as they're so frequently advertised for but at least they fit the color scheme.