You're not growing the A. tuberosa with enough sun and/or not lean and mean enough.

What do you mean "lean and mean enough"?

They are under a 300 watt grow light and all the other plants are thriving. The ones I planted are in full sun with zero shade all day.

Low water, low fertility....lean and mean.

That could be it in both cases. When I had my yard landscaped the landscaper setup my drip system to run for 1 hour twice a day, the ground was soaked. Also this was in soil I amended with compost.

As for the potted plants, I used Miracle Grow potting mix amended with compost. I assume the Miracle Grow had slow release fertilizer.

I attached a photo, from it you can see how well the Curassavica is growing vs the Tuberosa. I am assuming the Curassavica is more friendly in fertile soil?

That's about par for the course in greenhouse conditions (and greenhouse soil)...don't worry about them...plant them out this fall and they'll be fine next spring.

I'd really recommend don't keeping tuberosa in pots over winter...they go dormant and rot easily.

Curvassica as you should know...is a tropical and will not make it through frost.

Hmm, so I bought the Curvassica seeds off eBay, the seller stated they were from zones 5-9, I didn't realize they wouldn't overwinter.

You said you don't recommend keeping the Tuberosa in pots over winter, how do you think the Curvassica will handle it?

Is there another milkweed that you would recommend that would overwinter fine?

Curvassica is a tender tropical and grows like a weed, I'm sure you can keep it in a pot with enough warmth and light.

The native milkweeds, other than maybe incarnata, swamp milkweed, don't like pots...esp when dormant and tend to either A) dry out and die if you don't water or B) rot if you do. Best advise is transplant them into the garden in September, be sure to harden off carefully.

Your mileage may vary...

I agree with everything dbarron says and would just add to it. These two plants have totally, completely, enormously, almost opposite needs and habits, except that they both want sun and plenty of it. Tuberosa is a long-lived perennial of the temperate zone IF it has well-drained soil. Over-watered or in poorly drained soil, it will suffer root-rot. You cannot keep it in a pot, it has to be planted out in your zone.

Curassavica is a tropical species and will not overwinter for you except in a greenhouse or greenhouse-like conditions. It likes lots of water and it exhausts nutrients rapidly, so probably needs feeding to prosper. The eBayer who told you it was hardy to your zone was way off base.

As to your original question, why is tuberosa small and falling over while curassavica is tall and erect, that's partly because of light (not enough for tuberosa) and mostly because of habit. Curassavica always grows straight up and erect, and it grows, as dbarron says, like a weed, maturing in its first year to flowering and fruiting (in fact, it does so half-way through its first year). Tuberosa is one of the slowest species of milkweed to mature, never flowering in its first year, often taking up to three years to reach maturity. But tuberosa, if you give it a good sunny spot with decent soil, will reward you for a lifetime, whereas curassavica will evaporate within a year or two.

I am debating on keeping some of the Curassavica in my basement over the winter and planting it in spring, I hear the monarch cats love it over any other milkweed. Also I hear that monarchs look for fresh growth when laying eggs, so I may just start some of these every year for spring planting. I won't be able to keep them all, I have around 70 plants.

I have around 30 Tuberosa and bought another 21 orange in pots and am trying to find 21 of the Hello Yellow variety. I also have some seeds for Incarnata, Speciosa and Syriaca, I am thinking of putting out some seeds in winter as I understand they need cold stratification.

My main concern is that I don't have wonderful soil, it is mostly clay/silt. Will the Tuberosa work out well in this soil or should I switch focus to another variety?

Try mixing some builders sand into the area where you will plant the tuberosa. It will allow for better drainage plus perhaps raise the growing area a bit. Tuberosa is probably the least picky of milkweeds regarding soil EXCEPT it does require good drainage. I have seen lovely Tuberosa growing on steep banks in the wild, without benefit of water or nutrients, other than rain and whatever nutrients the native soil provides. Very hardy milkweed if needs are met. Since you have the plants already started, if it were me, it would be worth the effort to amend the soil and plant them out. If they become established, you will be rewarded with a long spell of blooms each summer. Pinch them back following the first flush of blooms and you will get a second round of blooms if your growing season is long enough.

Second year Tuberosa started from seed:

{{gwi:84806}}

Many types of butterflies adore the nectar

Mary

The A. tuberosa plants I started from seed this spring were very floppy in my yard, an area that gets full sun, no shade at all. I'm pretty sure it's the soil -- a silty clay loam I had previously amended with compost. I used some rocks to prop them up (the stems themselves are fairly stiff, they just tend to bend down near the base) and they looked okay.

We'll see if they survive the winter (could be a problem if it's a wet one) and how they do next year. I've got them surrounded with grasses, mostly prairie dropseed, with the idea that the grass will help keep them upright in the future as it fills in.

I've seen a few adult monarchs around them recently, the first I think I have ever seen in my yard.

Once my a.tuberosa seedlings got into the ground, they straightened right up. I have 2 flats hardening off outside and they are very floppy. I'm going to hurry up and plant them, hopefully they'll be happier.

For anyone searching this forum for milkweed/monarch info, I want to remind people that monarch experts are warning against planting the tropical milkweed. There is much debate on this issue, but I think we should proceed with caution when it comes to tropical milkweed.

If you are planting milkweed for monarchs, please consider using species native to your area. There are milkweeds for different soil types and conditions--though most do best in poor soil.

For people growing tropical milkweed in non-tropical areas, advice from the monarch enthusiasts is to cut it back in winter. It does provide food for monarchs.