How to get milkweed to germinate

I won’t lie, milkweed is a pain to get started. Once its germinated and a seedling, it’s an easy keeper. But it takes some knowledge to get there! Here are my tips from many a failed attempts over the years. Numerous seeds were tossed in this learning process! Cheers for a more successful experience than I had! And for context, I am in USDA Zone 6b.Getting started: Anatomy of a Seed
The most familiar characteristic of milkweeds is that its seeds are dispersed by the wind using a fantastic plume of fibers. This fluff is often called a “parachute” in grade school and a “coma” in botany.

Did you know?

In World War II, Americans collected milkweed seed pods for the fluffy down, called “floss” in these newspaper articles, which were used for life preservers and aviation jackets.

Calgary Herald
29 Aug 1942

Norfolk Virginian-Pilot 18 Sep 1942

The Salt Lake Tribune 21 Jun 1942

The San Francisco Examiner 10 May 1942

The pointed end where the fluff was located is the business end of the seed. It is where the embryonic root (the radicle) will push out of the seed coat. A plant growth hormone (auxin) will align the radicle to the gravitational pull thus this early taproot will seek the ground and water. Likewise, auxins and exposure to light will extend the hypocotyl, eventually emerging from the seed coat as the young plant stem with the seed leaves (cotyledons).

Getting Ready: Seed sorting
Open your seed package and check out your population of seeds. Look for fat, thick, large seeds where you can see the outline of the embryo. These are the best candidates for producing viable plants.

Pollination for milkweed flowers is dependent on insects, thus it is not surprising that some of the seeds are not plump or large. This is because that ovule was not fertilized by pollen. These seeds are not viable and may be discarded.

Some seeds may be folded. This happens when the seed is drying. Don’t worry about flattening them out. However, if the seed is broken and the embryo exposed, it is no longer viable. Seed breakage is common in the mail. Discard any with broken seed coats. If only the outer wing is broken, then the seed should be okay.

A mature milkweed seed

A mature milkweed seed

Crinkled and small seeds

Crinkled and small seeds

Non-viable seeds (trash)

Non-viable seeds (trash)

Stratifying Your Seeds
When milkweed seeds are fully ripe and dry, the embryo goes into dormancy. If you are planning to store seed for a longer period of time, such as until the spring, store the seeds in your freezer. This is called dry stratification and works for some seeds. I store mine either in a zipper plastic bag with seed envelopes in them or transfer to recycled glass bottles with a secure lid.

Milkweed requires moist stratification. Like with peas, water “wakes up” the embryo which is then waiting for cooler temperatures. Unlike for peas, sometimes this process takes several months for milkweeds. My last batch I started in September and achieved widespread germination in April.

I’ve found that moist stratification can be successfully achieved in one of two ways:

Fall Direct Sow
I’m sowing out a number of hardy annuals, bi-annuals and perennials this fall. If the first hard frost hasn’t happened by November 18, I am pulling everything out and putting my 2023 crops in the ground! For all of my fall planted direct sow seeds, which are able to be individually picked up (larger seeds), here is my process:

  1. Soak in room temperature water over night. This is to make sure that the seed gets fully wet.
  2. Identify and CONFIRM where you are planting your milkweed. These plants do not like to have their roots disturbed.
  3. Prepare your soil with organic matter (compost) but no additional fertilizer or manure. Milkweeds aren’t fans of quality soil! The goal is that there is good soil structure and that the ground is aerated for the young roots.
  4. Using your thumb, make a small indentation where you plan to plant a seed, set the seed on its side or with the pointy end going into the earth. Lightly cover with seed (¼ soil). Or simply scatter the seeds and cover with ¼ inch of soil.
  5. OPTIONAL: My biggest factors for failure are squirrels disturbing my seed beds and slugs. From my work with hellebores, I’ve learned to put down a light covering of chicken grit (oyster shell bits) over my seed beds. It discourages the squirrels and the slugs seem to leave them alone.
  6. For milder climates, you may see a seedling emerge before the hard frosts. For colder climes, a seedling will likely emerge as temperatures rise above freezing.
Napkin method
This method is borrowed from some great advice from online videos! Thanks to gardeners before me that figured out this trick.

  1. Insert one fast-food napkin laid out flat into a plastic sandwich size zipper bag.
  2. Label the bag with the name of the seed, the date you are starting them, and any other information you would like to record. Sharpies do work for this. Or use an oil-based permanent marker.
  3. Dampen the napkin with a squirt bottle. Do not over moisten the napkin. If water runs out, its too much. Make sure the whole napkin is saturated with water.
  4. Insert your seeds. Make sure that they don’t overlap so that you can easily see root development. Bonus: Get them all pointed in one direction to help you figure out which side to watch!
  5. Zip up the bag and make sure it is sealed and airtight.
  6. Place the napkin flat in the refrigerator. Do not put into the freezer as the embryo will go into dormancy until the temperature is above freezing. To save space, consider taping it to the underside of a shelf.
  7. Wait and check on them. Some seeds will germinate in several days. Other seeds won’t germinate for several months. Be patient! I give up after my last, last frost date which is Mother’s Day.
  8. Once a root is visible, remove the plantlet from the bag. Do this many times to remove each seed as it germinates. I recommend using blunt end tweezers to carefully remove the seed. Do not grab by the plant structure. Instead, gently grab the brown seed case.
  9. Plant outdoors if the temperature is above a daily low of 32 degrees OR plant into a 2 inch pot (or soil block) using moist unamended potting soil. These seedlings will do great in an unheated greenhouse.
  10. Plant out once you are past your last frost date, although I plant young milkweeds out with my early crops around St. Patrick’s Day.

Thyme in a Bottle is a tradename of Searfoss & Associates. Copyright 2022. All rights reserved.

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