University of Minnesota

Finding, Collecting, and Growing Milkweed

Finding and Collecting Milkweed

Common milkweed, A. syriaca, growing at a park in Minnesota. (Photo: Wendy Caldwell)

Most milkweed species grow particularly well in disturbed areas, so start by looking in the following places: roadsides, pastures, along railroad tracks, bike paths, highway medians, agricultural field margins, vacant land, cultivated gardens, and parks.

When collecting milkweed foliage to feed to caterpillars, it is best to pick the entire plant (check for other invertebrates first to ensure that you don't take any unexpected critters home with you). You can pick several days worth of milkweed and keep it in a plastic bag in the refrigerator. Wash it in water before using it. Milkweed stays fresher if you keep the end moist by wrapping it in a wet paper towel and then covering it with aluminum foil, or use florist water tubes or soda bottles. Potted plants can also be purchased from your local nursery, but make sure that they have not been treated with systemic insecticides before feeding them to your monarchs (ask the grower if you aren't sure). 

If you plan to grow your own milkweeds, or add milkweeds to your current site, you can collect seeds when the milkweed pods are ready to burst (this occurs in the fall in the northern U.S.). Once you have collected seeds, remove them from the pods and store them in an airtight container in a cool and dry environment (such as a basement or garage) until you are ready to use them. It is best to include a moisture remover (i.e. Silica gel) in your seed storage container. If the seeds are moist for a long period of time, they will start to rot and eventually die. Seeds collected in the Northern US will not germinate without cold stratification. 

Growing Milkweed

Milkweed being cultivated in a greenhouse (Photo: Chip Taylor)

Most seeds of temperate plants should be vernalized (cold treated); this ensures a higher germination rate than if seeds are sowed without this pre-treatment. Many of the southern species, such as tropical milkweed, will grow without cold-treatment. The most successful means of milkweed vernalization is through stratification. By stratifying, or subjecting seeds to a cold/moist environment for a short period of time, you simulate the conditions of a seed's natural break of dormancy that occurs when the seeds spend the winter in the ground. To stratify, first obtain a substrate. Peat has been found to produce the best results, in addition, peat/clay also work well. Secondly, moisten the substrate with water and place the seeds in the cold soil. Store the seeds in a dark place (a refrigerator crisper works well) with a temperature of approximately 5°C for a minimum of 3 weeks up to 3 months.

To allow for natural stratification, sow collected seeds directly into a mulched bed in the fall and the seed will germinate the following spring.

If you have grow lights or a greenhouse, it is best to start your milkweed seeds indoors a couple of months before you are able to transplant them outdoors. We fill the seedling trays approximately ¾ with potting soil (light, well-drained soils work best for most species) and scatter 3-4 seeds per cup and then cover the seeds with an additional ¼ inch of soil. The soil is then fully saturated with water and placed either in a sunny window or directly under the grow lights; they need a lot of light and warmth to germinate and grow. It's best to keep the temperature at 26/24°C day/night with a 16-hour photo phase. Keep the soil moist, but don't overdo it. If the seedlings are too wet, fungal growth can occur and kill the seedlings. The seeds will take approximately 10 days to germinate. Once there are 4 true leaves on the seedlings (the seedlings will be approximately 3 inches tall), the plants can be transplanted into your garden. Most milkweed species do best in full sunlight, so choose an open area with lots of sun. Plant the seedlings 1-2 feet apart. The seedlings should be watered frequently; mulch can be used to help hold in the moisture around the plants.

For indoor use, plant the seeds just beneath the soil surface using a rather deep pot, as they have a long taproot. Once the plants are in the seedling stage, fertilize once a week. To encourage fullness and more leaves, you can pinch off the top set of leaves (when there are at least two sets of leaves) to promote branching. It takes at least a month for the plant to be ready for the larvae to eat. Once the plant is big enough, you can simply place the entire plant, pot and all, into the cage. After the larvae have eaten the leaves, simply cut the plant off about two inches above the soil and new shoots will grow in 3-4 weeks.

When planting seed outdoors, keep in mind that all plants have optimal soil temperatures for germination, which makes propagation a little more difficult. It is best to plant the seeds as early as possible, but make sure that you plant after the last frost.

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