Plants→Milkweeds→Tropical Milkweed (Asclepias curassavica)

We have to grow Tropical Milkweed as an annual here as it dies out in the winter. Still, it is well worth it to plant the Tropical Milkweed each year, as once it starts blooming, it just continues to bloom all season long. And those flowers are bright and very pretty. It is a host plant for Monarch caterpillars.

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Tropical Milkweed (Asclepias curassavica) is a larval host plant for the Monarch and Queen butterflies, and an important Monarch Way Station plant. It is an excellent source of nectar for late season butterflies and moths, drawing a variety of pollinators. Hardy in zones 9-11, it will grow to full height and bloom prolifically in a single season in cooler zones. Look for Monarch eggs on the leaves!

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Asclepias curassavica is poisonous to humans and it is deciduous in zone 8a, but it comes back from the roots in spring.

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Beautiful plant that does well here in Tennessee and attracts butterflies galore. Will die to the ground after hard frost or freeze. Easy to collect seeds from the large pods when they split open.

Milky sap from broken leaves or stems can cause severe eye irritation.

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In the warmest zones, 9b-11, plant can reach 6'x4' and remains evergreen. In Dec 2011-Jan 2012 there were 75-100 monarch cats at different instars feasting on a huge plant in my yard - Texas Gulf Coast.

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Ophryocystis elektroscirrha (OE) Protozoan Parasite

Milkweed when planted in warm environments like southern Texas and the U.S. Gulf Coast doesn't die back in the winter like native milkweed does. When presented with a place to lay their eggs year-round, many monarchs don't bother making the trip to Mexico at all. Year-round tropical milkweed presents an even more direct threat to the butterflies. Milkweed hosts a protozoan parasite called Ophryocystis elektroscirrha (OE). Caterpillars ingest the parasite as they feed on milkweed. When they hatch from their chrysalises, the butterflies are covered in spores. It's a debilitating parasite. Infected monarchs are much weaker than their healthy counterparts and don't live nearly as long. In fact, if an OE-infected monarch tries to migrate, it will probably die long before it arrives in central Mexico. The migration is vital to keeping OE under control in the North American monarch population. Migrating "weeds out some of the sick monarchs every year," preventing them from passing the parasite along to their offspring. What's more, it gives the monarchs a chance to leave behind contaminated milkweed plants, which then die off during the winter. When the butterflies return in the spring "they start over fresh" with new, clean milkweed. But if the monarchs aren't migrating, and the tropical milkweed isn't dying off, OE never goes away.

There is some good news. Nearly all tropical milkweed in the southern United States is in gardens. A way to reduce the contamination: CUT THE MILKWEED DOWN TO THE GROUND IN NOVEMBER BEFORE THANKSGIVING. CLEAN YOUR TOOLS BEFORE CUTTING AND AFTER CUTTING WITH A RATIO OF 1 PART BLEACH TO NINE PARTS WATER TO DISINFECT YOUR TOOLS TO PREVENT CROSS CONTAMINATION. By cutting the milkweed down before Thanksgiving, you will prevent the contamination.

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Scarlet Milkweed is an evergreen perennial that does well in full sun to partially shady locations of the garden. It has beautiful orange/red blooms in the summer months that attract butterflies. Scarlet Milkweed is also a larval host plant for the caterpillars of the Monarch Butterfly.

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Tropical milkweed grows very well in my zone 7 Maryland garden as an annual, may self sow a bit. Easy to root from fall cuttings and can be kept inside over winter that way, and will grow quickly once planted back out. Monarch caterpillars do love it. Can get aphids some years, watch for aphids if you bring in seedlings or cuttings over winter..

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I read this recently in a local paper. "Tropical milkweed becomes a problem when planted in temperate areas where it does not die back in winter. A protozoan parasite of monarch butterflies (Ophryocystis elektroscirrha or OE for short) can travel with monarchs visiting the plants and become deposited on leaves. When caterpillars hatch and start eating the plant, they ingest the OE. High OE levels in adult monarchs have been linked to lower migration success in the eastern monarch population, as well as reductions in body mass, lifespan, mating success, and flight ability."
I assume this also applies to Southern California.

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