However, Asclepias tuberosa seeds will break dormancy after time. Our seeds have already broken dormancy and will germinate readily within a week or two after planting – no cold stratification needed.
Asclepias tuberosa Native Plant Range
USDA, NRCS. 2016. The PLANTS Database (http://plants.usda.gov)
To plant the seeds, press them into the surface of the soil and barely sprinkle them with about 1/16″ of dirt since light helps with their germination. Use about 2-3 seeds per final plant. Plants should be spaced about 18″ apart.
Use of Butterfly Weed in a Butterfly Garden
Asclepias tuberosa is a native milkweed to most of the US with the exception being the Northwest. It is a perennial and is hardy in zones 4-9. Some resources include zones 3 and 10 as well in its hardiness range.
Monarch butterflies use many different varieties of milkweeds to feed their caterpillars. Butterfly weed is one that they will use but it is usually not their first choice. In general, if there are other varieties in your garden they are likely to lay eggs on them first.
There will be sporadic blooming during the first year if planted in the spring but the following summer will yield much stronger, blooming plants. You can also start seed in the summer and plant in the fall for summer blooming plants the following spring. Butterfly Weed is late to come up in the spring so don’t give up too soon if it is not up early.
This is one plant that can tolerate a wide range of soil conditions from medium to dry moisture levels. It needs good drainage and is drought tolerant. This is a great milkweed for a sunny dry area. Butterfly weed prefers full sun but will do well in part shade.
Preferred growing conditions:
Milkweed (Asclepias) seeds germinate best under warm soil conditions. The seeds need a cold, dormant period, known as stratification, to germinate.
Dry stratification is done by placing dry seed in the refrigerator for 30 or more days. A more effective strategy is to moist stratify them by mixing seed with moist (not soggy) sand in a zip-lock plastic bag and place them in the refrigerator for 30 days. After 30 days of cold moist storage, the seed’s natural chemical germination inhibitors have dissipated and are ready to sprout.
Planting Milkweed Seeds:
To determine if a plant is sufficiently cold hardy, the USDA created numbered zones indicating winter low temperatures; the lower the zone number the colder the winter.
Asclepias (Milkweed) are sun loving plants that are essential perennials for monarch butterflies providing food for caterpillars and nectar for adult butterflies. They bloom from mid-summer into early fall and, with their milky sap, are resistant to rabbits and deer.