10 Sep Tips to Planting Milkweed for Monarchs
*This post has been adapted from milkweed planting instructions provided by Rich Haydon and Mike Hiler.
Milkweed is the only host plant for monarch butterflies. Adult butterflies lay eggs only on milkweed, and hatched caterpillars eat milkweed and only milkweed. Therefore, cultivating a healthy milkweed population is essential to supporting a healthy population of our iconic western monarch.
There are many species of milkweed. Make sure you’re planting a native species that won’t do more harm than good. At CCC events, we’re handing out showy milkweed (Asclepias Speciosa) seeds.
Showy milkweed is one of our native milkweeds, commonly seen blooming along highways and ditch banks around Yakima County. Besides boosting monarch populations, it has many other benefits:
- Low toxicity compared to other milkweeds, so it’s safer for kids, pets, and livestock.
- Long bloom period (two to three months) and sweet-smelling purple blossoms.
- In addition to monarchs, it attracts pollinators like honeybees, hummingbirds, and a host of other butterflies;
- And it’s easy to start from seed!
Planting milkweed from seed
Milkweed seeds are naturally spread in the fall by wind when its large pods release seed parachutes. To propagate milkweed, we mimic nature. Casting or planting seeds in the fall offers the best chance of success.
Here are a few best practices:
- Cast milkweed over light, well-drained soils that have adequate spring moisture. Showy milkweed prefers wet areas of prairie habitats and moist, sandy soils along waterways, ditches, stream banks, floodplains, and wash bottoms.
- Milkweed does best at the outer perimeter of riparian vegetative zones. Broadcasting seed too close to the riparian center can put milkweed at a disadvantage because it doesn’t compete well with thick riparian vegetative thickets.
- Seeds can be spread any time in early spring, but the site must have enough moisture for the seedlings to germinate and become established before soils dry out in the summer.
- Milkweed plants can tolerate drought, but you’ll want to assure a water supply when the seed is developing in late spring and early summer.
- Milkweed plants have extensive rhizomes and many of the stalks in a milkweed thicket are from a single root system. You can create an edge to a thicket by cutting off this root system, or by working the soil down several inches.
Starting milkweed in containers for transplant
Starting milkweed under controlled conditions can yield greater success than planting seeds directly outdoors. Here are a few best practices:
- Start the seeds in potting soil or in a natural soil that drains well.
- Seed germination rates can be improved by soaking the seeds for 24 to 36 hours prior to planting. You can do this by placing seeds between sheets of thoroughly wetted paper towels. Place the wet towels in plastic bags, but allow air space in the bags. They should be kept warm, around 75 degrees Fahrenheit.
- For planting, thoroughly soak the soil, then let excess water drain. Place the seeds on the soil surface about a half inch apart, then cover with about a quarter inch of additional soil. Gently water the soil surface to dampen the additional soil.
- After seeds have been sown, cover each pot or flat with a clear plastic cover or a plastic bag to keep the seeds from drying out.
- Place the planted seeds under grow lights, in a sunny window, or ideally in a greenhouse with reliable temperature control. Milkweed seeds will tolerate a range of temperatures, but the seeds and soil should be kept moist and warm – ideally about 65 to 75 degrees Fahrenheit. Most seeds will germinate in seven to ten days if adequate moisture and warmth are maintained. Over-saturated soil or excess heat need to be avoided, or the seeds may simply rot.
- After the seeds have germinated, remove plastic coverings from the pots or flats. Seedlings will do best if grow lights are used and the soil is kept moist by bottom watering. The soil should be kept moist, but over-saturated soil will result in fungal growth that can kill young seedlings. Inadequate light will result in weak plants with thin stems subject to disease.
- Milkweed seedlings are ready to be transplanted when they are about six inches tall and should be planted about 12 to 24 inches apart. Ideal transplant sites will have light (not clay) soils that drain well but have good spring and early summer moisture. Depending on the site and weather, transplanted seedlings may need to be watered on a regular basis during their first growing season.
Happy and successful planting!
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