The seedbed should be kept moist until germination. As the seedlings become established, it is important to avoid watering too much or too little. A light watering each day until roots are well established (7-10 days), preferably in the morning, should be sufficient.
The plants are ready to be transplanted when they are about 3-6 inches in height. Before transplanting, acclimate the plants to outdoor conditions for a few days by placing them in a sheltered location during the day and then bringing them indoors at night. The seedlings should be planted 6-24 inches apart depending on the species (check the back of your seed packets for information). Newly transplanted plants should be watered frequently. Add mulch around the seedlings soon after planting. The mulch holds in the moisture and minimizes the growth of competing weeds. The seedlings should be fertilized 2-3 times during the growing season if using water-soluble fertilizer or once a season if you utilize a granulated time-release formulation.
When small seeds are sown, they are often mixed with sand or fine soil to have better seed distribution. However, this method does not completely prevent crowding of seedlings and thinning will be necessary. Thinning provides more space between plants, increasing the amount of light reaching the plants and the air circulation around them. Seedlings may need to be thinned several times beginning 1-2 weeks after germination. Without proper thinning, you will end up with weaker plants.
Growing Milkweeds from Cuttings
All milkweeds are perennials and some can be grown from cuttings. Cuttings provide a way producing new plants in a relatively short time and it avoids some of the difficulties of starting plants from seeds. To start cuttings, cut the stems underwater, then coat the bottom of the stem with a strong rooting hormone. The stems should be placed in sand, vermiculite, or potting soil that is kept continuously moist. Cuttings can usually be transplanted in 6-10 weeks. Survival is best when cuttings are made from green stems (1/3 inch diameter) obtained from plants fertilized two weeks earlier.
Preparation of the Seedbed
If you are gardening for the first time, it is wise to consult with your local county extension agent to see if your soil needs to be enhanced (amended) with soil additives before planting the seeds.
If you have a choice, light soils are better than those with heavy clay. Well-drained soils are generally best but there are some species, e.g. A. incarnata (swamp milkweed) and A. sullivantii, which do well in saturated conditions.
Milkweeds can be propagated from seeds, cuttings, and, in some cases, from root divisions. This account will deal with storage, treatment and planting of milkweeds seeds and will briefly touch on propagation from cuttings.
11. 1-2 months after your seedlings have sprouted next spring, pinch off extra plants (or consider transplanting) to achieve ideal spacing for your specific milkweed. The Ascelpias viridis (spider milkweed) plants will be spaced 1.5 to 2 feet apart.
Fall planting is a great way to get your perennial milkweed varieties started, since the seeds will need cold stratification…and Father Winter takes care of this naturally! Consider planting milkweed varieties that are native to your region for best results.
5. Repeat this process for each seed you are planting.
10 Simple Steps for Fall Planting Milkweed
Warm weather milkweeds, which are annuals for most of us, do not require this cold treatment. These varieties include tropical milkweed, swan milkweed, goose plant, and giant milkweed.
7. Cover the seeds with the already-moist soil. You can place a few inches of straw or leaf mulch over the area to keep the soil from drying out.
Measuring between holes: Make the letter L with your thumb and forefinger. Use the distance between the tips of each digit for approximate spacing. Seeds can move over winter and some won’t germinate so exact spacing now is a waste of time.
If you are buying seeds from a vendor, they should have instructions telling you whether cold stratification is necessary. If not, search for specific milkweed pages on this site or consult with Mother Google.