What is this plant growing in my garden?
Your plant is probably Erechtites hieraciifolia, American Burnweed. You may want to compare some photos from the internet.
I was hoping it was lobelia siphilitica.
They look incredibly similar when immature. If you have some reason to suspect they are lobelia (Are some nearby?), it's possible it is lobelia. We'd recommend that you let it grow for a while. As the plant matures, it will be increasingly obvious which one it is. For one thing, burnweed will be very tall and produce flowers that never seem to bloom, but pop open as mature seeds. Don't let it get that far.
Hopefully it will be lobelia!
yes, thank you I will. It will be wonderful if it is lobelia siphilitica a native plant that will attract hummingbirds!