Milkweed Collecting, Cleaning and Storage:
Cleaning Milkweed Seed: The ShopVac Method
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.
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.
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.
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.
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.