Starting Asclepias tuberosa From Seed

For years I had problems growing Asclepias tuberosa. The germination was irregular and the few plants I got failed to thrive, sputtering along and then dying after a year or so. Even when I tried buying 3" pots they never did well for me. Most of the time if I fail with something a couple or three times I just give up - there are plenty of other things I can grow really well so why sweat the failures? I felt this way about butterfly weed until I saw one growing all by itself out in the middle of an empty lot on (of all places) Research Park Drive. It was the nicest butterfly weed I had ever seen, thriving among a bunch of weeds and grass and apparently unfazed about getting mowed over every 6 weeks. Surely it can't be that finicky if it grows well under those conditions! This was a few years ago and I decided to read up and figure out what I was doing wrong.

The germination problem partly stemmed from inconsistent directions. Some catalogs say to just plant the seed, no special directions. This is what I had tried before. Stokes Seeds , which usually provides detailed and accurate germination information, says to press the seeds into the soil without covering them, pre-chill the planted seeds at 34-40F for four weeks, and then warm them up to 65-70F and expose to light. On the other hand, Norman Deno, who is usually considered the final authority on how to start anything from seed, says to pre-chill but that the seeds do not require light and should be covered.

I ordered the seeds from GeoSeed and had planned on following Deno's directions but forgot to start them early enough to pre-chill. I figured the seed wouldn't be good the next year so I just planted them in a flat, and this time they came up like radishes! The seed source may have made the difference, maybe it was luck, I don't know.

When looking into the "failure to thrive" problem I found that Asclepias tuberosa is taprooted and does not transplant well. Alan Armitage writes in Specialty Cut Flowers, "If the taproot is broken the plant takes two years to recover - if it survives". Armitage suggests transplanting the seedlings into 4" pots by the time the second set of true leaves appear and then later gently moving them again into the field. I didn't have time or space to deal with 50 4" pots so instead I decided to plant the tiny seedlings directly into their final positions in the field. I had to fuss with them a bit, keeping an eye on the weeds and watering, but most of the little plants survived. The following year I was finally rewarded with a bed full of robust Asclepias tuberosa that bloomed profusely and even re-bloomed later in the summer. I liked them so well that I decided to start some more this year. I'm going to start some with the pre-chill method and some without and will report how it goes.

Asclepias (milkweed, butterfly weed)

Asclepias is the genus of the butterfly weeds or milkweeds. I grow three different species of them for cut flowers, two perennial and one annual. All bear their flowers in clusters. Close up the individual flowers look very similar but they are all useful because they are different colors and bloom at different times.

The first perennial milkweed is Asclepias incarnata or swamp milkweed, which bears rounded clusters of white or pink flowers in mid to late June. The flowers have a sweet, vanilla or candy-like fragrance. It is fairly mild, it won't knock your socks off, but it is still pleasant. I know nothing about butterflies but they do seem particularly attracted to flowers with this type of scent. Asclepias incarnata is native to this part of North America but I have never seen it growing wild.

The second perennial variety, Asclepias tuberosa, is another wildflower native to this part of the country. It has brilliant orange flowers and you occasionally see it growing along roadsides. The flowers are borne on pointy clusters and appear in July. If you like the combination of orange and purple/blue flowers (one of my favorites), then you could try pairing this asclepias with blue balloon flowers (Platycodon grandiflorus). I have not written about balloon flowers yet but they bloom at the same time as the asclepias, and both are long lived and do not require division.

The annual milkweed I grow is Asclepias curassavica. The flowers are bicolor yellow and red with bronze stems and leaves. The flowers are borne in loose clusters and if cut for the house or deadheaded will re-bloom until they are killed by frost. Of all these milkweeds, this is the one people most often ask me about. These will frequently self-sow a bit in the garden but have never been a pest.