Growing Milkweeds

A monarch caterpillar feeds on Asclepias subverticilliata, photo taken early Septemeber in Chiricahua Mountains. Borderlands has this species of milkweed available for sale.

Milkweed Collecting, Cleaning and Storage:

Collecting milkweed seeds is an involved process: from the persistent observation required to get the timing right on wild seed collection to cleaning the fluffy seeds, milkweeds provide many challenges to the native plant horticulturist! Each seed is attached to a parachute of white floss that gets caught in the wind when pods burst open. We identify and monitor populations for collecting to get the timing right, but additionally use muslin bags as seed catchers tied around a ripening pod. Once covered pods burst, their seeds are trapped within the bag, allowing the collectors plenty of buffer time between the time the pods burst and the seeds are gathered. This is only effective in dry weather: once the rains arrive and the muslin bags get wet, seeds may rot and become inviable.

Ripe Asclepias subverticillata seed pod. Photo by Caleb Weaver

Information about the greater milkweed population is meticulously gathered alongside ripe seeds. Along with the species name, the following information is also collected with each accession: detailed directions to the population, its biotic community, watershed designation, population information, associated species, and abiotic location information. This information is compiled in our computer database and follows each accession of seed along the propagation train.
Seeds are then cleaned in a variety of methods. Small accession totaling a fewer than one thousand seeds can be carefully hand-separated from the floss and seed pods. Larger accessions can be separated from the parachute-like floss using a shop-vac with a filter. Adding the entire collection into a paper grocery bag, and shaking it vigorously, also produces good results.



Cleaning Milkweed Seed: The ShopVac Method

Piles of fluffy Milkweed seeds need to be cleaned, the fluff removed, before propagation.

When collecting milkweed seeds en mass, it is necessary to do bulk cleaning. Research has shown that the seed-dispersal mechanism (white silky fluff) inhibits germination in the seed when still attached. As a result, we have tried many methods to efficiently clean the fluff off of our seeds for propagation.

We purchased a shop vac with a paper filter & slowly feed the seeds into it. This is best done with a helper.

Shop vacs help agitate the seed in an enclosed container and thus are useful for cleaning. The seeds and fluff are slowly fed into the vacuum, where the fluff is caught in the filter and the seeds fall to the bottom. Seeds are removed by hand or poured through a 1/4″ sieve to remove any larger debris.



Seed Storage:

If at all possible, we recommend immediate propagation of the seeds you have just cleaned. Germination will be the best while the seed is at its dispersal stage, maintaining optimal moisture levels derived from the mother plant.

Our seeds are stored in a dry, dark environment guaranteed by desiccant packets that are added to each jar. Seed viability is best in the long run if kept at 40 degrees F and 20% humidity, to limit biotic activity but prevent complete desiccation.

Home storage is best accomplished by sealing seeds in a glass canning jar with a desiccant packet added, and storing in the fridge.



The concept of stratification is to increase germination times and percentages through tricking the seed into believing that winter has come and gone. This involves moisture and cold.

When to stratify: It doesn’t matter when you start stratifying your seeds if you have a cold frame, a warm sunny windowsill, or a greenhouse. If you only have a shadehouse or the seeds need to germinate outside, make sure that you plan for the seeds to start coming up after the last frost date. For example: if your last frost date is in the beginning of April, then start stratifying in November of December.


Ascelpias Glaucescens. Milkweeds can take many forms, but have distinct flowers. Do I need to stratify milkweed seeds?:

If you live in a lower elevation area that never gets very cold or freezes, you don’t need to stratify the seeds. The higher your elevation, the higher the likelihood that you need to stratify your seeds. Currently, BR is experimenting with stratification. The first year we propagated 11 species. We stratified all of them to be on the safe side and they all germinated (stratifying doesn’t seem to hurt the germination rates, it’s so labor and time intensive though, that if you don’t have to, why bother). Mid-elevation species that we’ve experimented with and don’t need stratification include: A. angustifolia, and A. asperula. Asclepias subulata is a low elevation species that doesn’t need stratification either.




Through Winter 2014 the BR Greenhouse grew out thousands of milkweeds (Asclepias) of 11 different species in partnership with Southwest Monarch Study.Step 1: A good rule of thumb when sowing seed is to bury the seed twice its diameter under growing media. The media we use at BR is a half sand, half fine mulch mix. I recommend well draining potting soil for milkweeds and other native plants that need drainage for root development. If you have organic compost or a fertilizer of sorts, a small amount mixed in with the potting soil is ideal in increasing growth and not stressing the plant.

Step 2: Once the roots of the seedlings have reached the bottom of the pot it’s time to transplant them. If you sowed the seeds in the 8” tubes, you can either transplant them out into your garden, or repot them into a bigger pot (a pot with a rooting depth longer than 8”). If you sowed them all together into a seed or gallon pot, I recommend separating them and transplanting them individually into pots and then waiting to pot them in the ground.

Step 3: It is ideal to plant potted plants in the landscape once the fear of frost is over, and during a time when it will be easy to water them. An ideal time in southern Arizona is at the beginning of monsoon season (early July). Definitely keep them well watered though, because in temperatures over 100 degrees, it might only take a day or two to dry out plants that aren’t established in the soil.



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    The mission of Borderlands Restoration is to reconnect wildlife, land, and people in the Arizona/Sonora Borderland region by involving people in restoring the ecosystem on which we depend.

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    299 McKeown Ave, Suite #3
    Patagonia, AZ 85624

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