I was curious if planting milkweed would really bring in a monarch. Hadn't seen one since I moved in 3 years ago. Planted swamp milkweed and butterfly weed this spring. Worked great, lots of caterpillars and monarchs already on just 8 plants. They just needed a reason to visit.
I planted mine in full sun, rich soil and watered it nearly every day. Really took off and they are over 3ft tall with a thick trunk. Next to them I planted butterfly weed. They are bushier and smaller but the monarchs lay their eggs on them, and then when they mature they move to the swamp milkweed. I have seen over a dozen monarchs now and they've been prolific with the eggs. Will expand this patch next year for sure! Good luck.