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Asclepias (speciosa)

Derek Tilley
PMC Manager
USDA NRCS - Aberdeen Plant Materials Center
PO Box 296
Aberdeen, Idaho 83210
208-397-4133 x 104

Family Scientific Name: Asclepiadaceae
Family Common Name: Milkweed family
Scientific Name: Asclepias speciosa Torr.
Common Name: Showy milkweed
Species Code: ASSP
Ecotype: Yosemite National Park
General Distribution: Western North America; British Columbia to Manitoba, south to TX.
Propagation Goal: Plants
Propagation Method: Seed
ProductType: Container (plug)
Stock Type: 10 cubic inch conetainer
Target Specifications: Healthy root development filling the 10 ci conetainer.
Propagule Processing: Pods left in a box or on a shop floor will split as they dry. The fluffy haired coma can be removed by vacuuming the hair and seed with a shop vac. The seed will separate out to the bottom of the vacuum while the hair forms an easily removable matt on the top. Seed is then cleaned using an air-screen cleaner with 5.50 mm top screen and 2.35 mm bottom screen and light air.
Pre-Planting Treatments: Seed is stored in cool-dry conditions with temperatures of approximately 10° C (50° F) and relative humidity of 20 to 30%. Showy milkweed seed is often dormant and requires a cold stratification treatment for germination; however this seed collection did not require any stratification for full germination.
Establishment Phase: We used Sunshine Mix #4. No fertilizer is added to the soil mix. Two to five seeds are placed on the soil surface and pressed for good seed-to-soil contact. Seed is lightly covered with approximately 1/8 inch of soil, and the soil surface is kept moist with 20 minutes of daily irrigation from overhead sprinklers for the first 30 days. Day time greenhouse temperatures range from 24 to 29° C (75 t 85° F). Night time temperatures average around 21° C (70° F).
Length of Establishment Phase: 8 weeks
Active Growth Phase: Our seed lot had very high viability and most cones had multiple plants in them. However, as showy milkweed doesn’t produce many lateral roots, we left 3 or 4 plants in each cone in an effort to get a nice tightly packed root system. After full establishment, plants are fertilized once per week with Miracle Grow All Purpose Plant Food (15-30-15). After 30 days the irrigation schedule is changed to 40 to 60 minutes every other day to encourage root growth. We had to trim our plants with an electric hedge trimmer periodically as they grew and began to affect the sprinkler distribution.
Length of Active Growth Phase: 4 months
Hardening Phase: We backed off the water to 60 minutes every 4 or 5 days.
Harvesting, Storage and Shipping: Plants were deeply watered just prior to shipping. Plants were shipped in a 10° C (50° F) refrigerated truck for 2 days.
Other Comments: By the time the plants were scheduled for shipment, they had gone dormant due to changes in day length. Plants turned yellow and began to lose leaves. The roots however should still be good for outplanting.


Tilley, Derek. 2016. Propagation protocol for production of Container (plug) Asclepias speciosa Torr. Plants 10 cubic inch conetainer; USDA NRCS - Aberdeen Plant Materials Center Aberdeen, Idaho. In: Native Plant Network. URL: http://NativePlantNetwork.org (accessed 2021/05/11). US Department of Agriculture, Forest Service, National Center for Reforestation, Nurseries, and Genetic Resources.

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