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Years ago I bought a packet of butterfly weed (Asclepias tuberosa). There wasn't much information on the planting instructions. I planted the seed and nothing grew. Well, I must have done something wrong or so I thought. Why not try again! And so I did with the very same results. I did find some plants at the local nursery which I purchased. I found that sometimes these plants do not make it the first year. Oh, how frustrating! Now I am finding that the local nurseries may carry more varieties of milkweed seeds and plants.
Here are some of my thoughts and tips on milkweed:
Many varieties of milkweed do not transplant well. They have long tap roots which resist being disturbed. Tuberosa is very resistent to transplanting. Another variety, 'Ice Ballet' swamp milkweed, easily transplants as I have bought it at the local nursery at three feet tall.
'Ice Ballet' Swamp Milkweed
Seeds are another matter. Some need to be stratified. (Tropical milkweed does not need this process.) That is a process of cold treatment. When we think of milkweed growing wild, the plants form pods which contain the seeds and when ripe they split open. The wind blows the seeds to various locations. The seeds keep through the cold winter and sprout in the spring. We can simulate winter. Collect the seeds and store in your refrigerator for the winter. I have heard that 6-8 weeks is all that is necessary. The next trick is getting the seed to sprout. I place the seeds in layers of wet paper toweling inside a tupperware type container for a few days. Check to see if the seeds have sprouted. You do not want these seeds to get moldy. When the seed sprout, you can plant them in the garden or in small pots. Do not grow too big and then plant in the garden. Each variety of milkweed is different, so it is hard to give any guidance on how long to grow a plant
Another method I tried was to soak the seeds in hot water for 36 hours, changing the water with fresh water after 12 hours. Surface sow, light needed for best germination in 1-3 weeks at 75 degrees.
Other suggestions and thoughts:
Milkweed can be grown in pots. I treat these as annuals.
Some milkweed can be invasive in your area, but not in my area.
Tropical milkweed can be grown as annuals in the northern regions.
If you live in a residential area, your neighbors may not want your free blowing seeds. Watch plants for when the pods split and pick before the wind blows them around. As the flowers fade, the seeds form. The plant uses energy to develop the seeds. Early in the summer, I pinch the faded flowers off. I desire more flowers to attract more butterflies. I may leave some seed form at this time. By August I allow more seeds to form if I desire to save seed.
Monarch caterpillars love the tender new growth. I planted some just started milkweed in my garden. They grew to about ten inches, when the monarch butterfly started to lay eggs on these plants. The caterpillars striped these to just stems. The next year these plants recovered and became normal sized.
Be sure to leave space between plants. This will aid the monarch butterfly with access to laying its eggs. They tend to lay their eggs on the undersides of the upper leaves which are the most tender part of the plant.
The eggs are a clearish-white that are no bigger than the period at the end of this sentence. They take anywhere from 3-5 days to hatch depending upon the weather.
It always amazes me how concealed the caterpillars can be.
There is also a moth that lays its eggs on milkweed, tussock moth. I read a book that stated the Grey Hairstreak lays its eggs on the tuberosa.
To attract butterflies, it is best to plant in masses. An area of 5-6 plants of the same variety will be more attractive than just 1-2 plants. The sweet aroma of the milkweed flowers attract many species of butterflies to my gardens. It also attracts many other insects; i.e. bees, wasps, etc.
The best advice that I can give to you is to experiment and see what works for you.