I have been collecting native milkweed seeds and growing them. Often I observe a low germination rate from seeds off struggling plants and near 100% with those from healthier garden plants. Both seeds are viable and swell up just fine but the wild ones have problem with root emergence, some even have cotyledons coming off the side with roots stuck. I am wondering if the seed coat is too thick and hard, as the side effect of stress response to tough up cell walls against pests.
It's part of the nature and maybe weathering and digestion by soil microbes will help the seeds germinate. But honestly, I broadcasted milkweed seeds in the past by the thousands and had less than 0.1% germinated. I wasted two years to get the green flowered milkweed to grow naturally so I am intervening this time with indoor stratification and scarification.
As seen in the pictures below, scarified seeds germinated in 3 days evenly, though it took some practice.
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Common milkweed seeds germination test
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Plant seeds with roots and clipped the rest
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Another 2 days later, newly clipped ones germinated
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