By Jordan Isken, Production Manager
At the winter plant sale this last weekend, one of the most frequent requests from customers was for milkweed plants. The most common species that we grow at TPF, in order of popularity, are narrow-leaf milkweed (Asclepias fascicularis), showy milkweed (A. speciosa), and Kotolo milkweed (A. eriocarpa). All three are essential habitat plants for the western population of the beloved monarch butterfly, and their seasonal winter dormancy is an important cue for the monarchs to stop laying eggs and migrate to an overwintering spot along the coast. In the garden, these milkweeds are not only appreciated as a host to butterflies and insects alike, but they also provide greenery and flowers deep into the heat of the summer before retreating underground again in the fall. Milkweeds apparently love the heat, as the plants do not reemerge until the warmer months of late spring, and the seeds do not germinate until this time either. Due to this winter dormancy, we are unable to sell plants until they have come out of dormancy and, due to germination cues, we must wait to sow the seed.
Alas, it is impossible for TPF to offer California native milkweed plants at this time of year. But I hate to have unsatisfied customers, so below I have detailed exactly how we grow milkweed seed, so that you might be able to start your own this year from
home (with seed purchased from our shop!).
As a grower, I must admit that milkweed is one of the easiest plants that we grow…by far. Its predictable and uniform germination makes it an excellent candidate for first-time seed sowers. The first, CRITICAL step is to wait until we get warmer temperatures. At the earliest, you can sow the seed in March, but germination can be achieved all the way into July (sowing any later than July is risky, as the plant needs to be robust when going into dormancy).
Here at TPF, we sow the seeds into small plug trays, but any container (preferably one gallon or smaller) will work. Start by filling your container with any seed-starting or high-drainage potting medium (typically cactus mixes or anything with added perlite, including TPF’s own custom mix). Dig a small hole about 1/2 inch deep and place anywhere from 2 to 4 seeds and lightly bury. After the seed is sown, give the pot a good soak and make sure to wet the medium entirely. Place your container outdoors in full sun. Allow the surface to dry down before watering again, but keep in mind that your seed is in the top inch of the soil that needs to stay moist, so don’t let it dry down too much. Your watering schedule will likely be every 2 to 3 days. Once the seeds have emerged, they will begin to drink up the water and watering will be more frequent, particularly after the plant starts putting on growth and begins to fill .the pot with roots. If multiple individuals germinate in your pot, you can thin or leave them clustered. Milkweed seedlings don’t seem to mind growing in
Another option is to sow the seed directly into the ground. The instructions above are roughly the same for in-ground germination. You want to find a spot in a sunny location that is not competing with nearby plants (at least until your seedlings are established). Lightly bury the seed and scrape away any mulch or leaf litter that might inhibit the sun from reaching the soil. Wet the ground periodically to ensure the soil stays moist where the seed has been planted.
Of course, if your seed sowing is unsuccessful, you can always buy the plants from us. They are offered late spring all the way through the fall. Be sure to check our online inventory for availability.