I have milkweed growing in my garden. I planted it towards the middle of this area because I thought it was the same plant that I see growing alongside the highway. I know that they have a very long taproot and don’t like to be moved, but this baby is almost 5′ tall. My question is, would it adversely affect the plant if I pinched off the growth shortly after it makes its appearance in the Spring/Summer in the hopes of getting a bushier, and shorter, plant? I don’t want to do anything that will cause it not to bloom. Additionally, in my research of planting from seeds, it said to put them in the fridge for 3 months before planting. Is this length of time absolutely necessary?
There are many types of milkweed. I'm wondering if you have "common milkweed". It isn't likely to get taller; it will now turn to seed formation. Most milkweed seeds must go through cold moist stratification: the exact length of time varies by species. This is true of many native plants except grasses. If it is too tall, switch to a variety that is smaller. This will work much better than trying to curtail height by cutting the growing tip. Pruning will likely increase suckering which is already a problem with common milkweed. You should grow what is native to your region. Sullivant's and swamp milkweed are less likely to sucker aggressively and butterfly weed is the shortest of the milkweeds. This article gives comprehensive information on propagating milkweed. https://www.monarchwatch.org/milkweed/prop.htm
This website has valuable information on growing a monarch-friendly garden. Monarchs have favorite flowers as food sources; they need these flowers as much as milkweed for egg-laying. https://www.wildflower.org/project/project-milkweed