Could chemicals used for lawn care remain in milkweed seeds?

Question

I want to use the milkweed in raising monarch butterfly caterpillars. A neighbor has offered seeds from her milkweed, but the adjacent lawn has been treated with various substances by their landscaping company. Could any fertilizer, herbicides, etc. remain and affect the plants grown from these seeds which would make them unsuitable for the caterpillars?

Answer 1

There is no fast answer to this question. We can assume the plants were not sprayed directly. How far are the milkweed from the lawn? Lawn herbicides are typically contact herbicides so a light coating is all that is needed. I don’t think much makes its way to the milkweed roots. However, some weed killers remain in the soil for up to 18 months. These are mostly for agricultural use. The amount of herbicide that makes its way to plant seed would be very small amounts; however, a caterpillar is very small too.
Milkweed seeds are available from mail-order native plant nurseries. There are over a dozen types of milkweed. Make sure to use seeds of types native to your region. These will be the types that monarchs in your region are looking for. Follow this link to find a source for your native milkweeds. https://xerces.org/milkweed-seed-finder/
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/how-long-does-weed-killer-last-in-the-soil.htm

Answer 2

Thanks for this; I don’t think I’ll take the chance with the neighbor’s seeds. We do have a nursery nearby that is a monarch way station and sells “safe” seeds.