- Author: Penny Pawl, UC Master Gardener of Napa County
Spring is in the air and it is time to plant milkweed for the Monarch butterflies. Milkweed (Asclepias) provides food for the butterfly larvae, and its flowers provide nectar for the other pollinators in our area.
Butterfly numbers have decreased because of milkweed removal and the use of pesticides. The Monarchs need all the help we can give them.
If you would like to plant milkweed, choose varieties that are native to our area. They have adapted over time to our climate, soil and conditions.
The two most common natives are A. speciosa (showy milkweed) and A. fascicularis (narrowleaf milkweed). Both types grow in Napa County and are drought tolerant. One came up in a crack in my driveway last summer and survived the entire summer without a drop of water. The only thing it did not have was any butterfly eggs.
One way to plant the seeds is to mimic nature. In a natural setting, the mature seed pods open and wind scatters the seeds. To imitate this process, choose a site where you want the plant to grow, scatter the seeds and push them into the soil with your hand or foot. Do not cover the seeds with soil as they need sunlight to germinate. This seeding method is most effective before the soil and weather warms as the seeds need to go through a cold period to germinate.
If you miss this window of opportunity, you can try another method that I have used successfully. Put the seeds on damp sand in a container with a lid and refrigerate for at least a month.
After that chill period, you can plant the seeds indoors in soil and put them under a grow light or on a heat pad (or even both). If you keep the soil warm and provide plenty of light, the seeds should germinate in a week or so. After they sprout, you may need to increase the light so the seedling does not become leggy. Some growers suggest using peat pots so you don't disturb the roots when you transplant.
You can also wrap seeds in damp paper towels and keep that bundle in a baggie in the refrigerator for a month or so. Then you place the seeds, still wrapped in paper toweling, on the soil with a heat mat underneath. The roots will grow into the soil right through the paper towel. I have used this method several times to germinate tomato seeds.
The water germination method takes a little more labor but also works. Put the seeds in fresh non-chlorinated water warmed to about 80ºF degrees on a heat mat. Twice a day, drain the water and replace with fresh water, checking the temperature with a thermometer. Viable seeds will germinate in 2 to 7 days. Any seeds that don't germinate can be refrigerated for a month and then you can try again.
Some people clip the edge of the seeds with a nail clipper to break the seed coat and make it easier for water to penetrate. Then they place the clipped seeds on damp soil with heat underneath. The clipping takes time so I have never done it.
However, I have propagated both kinds of milkweed in summer using a cloner. To do this, cut a 12-inch growing stem, remove any lower leaves and insert the stem in one of the cloner's holders. Make sure water washes the bottom of the stem. Be patient; it can take some time for the stem to grow roots.
Some native milkweeds spread by the roots and turn up where you don't want them. I have dug up native milkweeds and successfully transplanted them. One fall I dug the roots up, wrapped them in paper towels, put them in a plastic bag and refrigerated them over the winter. When spring arrived I replanted the roots successfully in a new bed in my garden.
I consider all this effort a labor of love. I love to see the baby Monarchs mature and turn into beautiful golden butterflies. Plant some milkweed now and you can help them thrive this summer.
Workshop: Join UC Master Gardeners of Napa County for a “Backyard Compost Workshop” on Sunday, March 26, from 10 a.m. to noon at Hagafen Winery, 4160 Silverado Trail, Napa. Learn about hot composting, cool composting and worm composting. At the conclusion of the workshop, you may purchase a discounted compost bin for $20 (one per household). Register here.
Library Talk: Join UC Master Gardeners of Napa County and Napa Library for a free talk on “Introduction to Companion Planting” on Thursday, April 6, from 7 pm to 8 pm via Zoom. Companion planting uses plant partnerships to create a habitat in which all organisms thrive. Register to receive the Zoom link at
Help Desk: The Master Gardener Help Desk is available to answer your garden questions on Mondays and Fridays from 10 a.m. until 1 p.m at the University of California Cooperative Extension Office, 1710 Soscol Avenue, Suite 4, Napa. Or sSend your questions to email@example.com. Include your name, address, phone number and a brief description of the problem. For best results, attach a photo of the plant. You may also leave a voicemail message with the same information at 707-253-4143.