Interesting, and sad. I hadn't heard this. I have only native milkweed on my property, but the numbers of monarch butterflies I've been seeing are at record lows. I saw only two or three last year. Migratory species are the hardest hit because they have to run the gamut across farmland sprayed with roundup and other toxic chemicals.

I thought this potential problem with the tropical species was only true of areas where it does not die back but continues to flower throughout the Fall and Winter.

In any event, I saw my first Monarchs yesterday in my yard (Zone 7/NJ). My "butterfly plants" include purple coneflower, black-eyed susans, large Buddleia bushes, Swamp Milkweed and, in about a month, the Tropical Milkweed.

Two years ago, I planted ONE of the tropical ones and now, every year, they are all over the front yard! The plant itself dies back some time in November after the first frost, but apparently the seeds are cold hardy and survive just FINE. I can see some might consider it weedy, but the flowers are gorgeous and the butterflies seem to love it!

I've been raising Monarchs for nearly 10 years and my property is a Monarch Waystation and yes I've heard this about tropical milkweed. There may be problems growing in the southern zones where Asclepias curassavica is perennial but not here in zone 6 (in my experience).

Our season just isn't long enough - often the tropical milkweed doesn't even have enough time to produce mature seed pods, before it's killed with a hard frost. What's more, as soon as it gets cold at night the Monarchs are out of here pronto (usually around late Sept/early October). There is no chance whatsoever they are going to hang around because of the tropical milkweed.

I grow common, swamp, purple, and orange (butterfly weed) milkweeds and it is a finicky genus - not all species do well every year, it is a target for insects, and it randomly dies back, so I grow a fair amount of the tropical because it attracts egg laying females to the garden. I then collect the eggs and raise them on whatever cuttings are doing well, the caterpillars are adaptable, and if I've got a lot of hungry 5th instar caterpillars to feed, will sometimes collect extra common milkweed cuttings from wild sources.