Growth Characteristics of Common Milkweed

Seed dormancy of common milkweed ( Asclepias syriaca L.) is broken by a few days of moist low-temperature after-ripening. The duration of low-temperature after-ripening of the seeds is temperature dependent. Seedling emergence is best when the seeds are planted 1 to 2 cm deep and extremely limited when planted 6 cm deep. Seedlings have the capacity to produce new shoots if clipped in the 1 to 1¾-leaf pair stage and multiple shoots if clipped in the 2 to 2½-leaf pair stage. All seedlings reaching the 4 to 4½-leaf pair stage before clipping produced new shoots.