Is Tropical Milkweed Bad For Your Butterflies? What You Can Do
Tropical milkweed is a harmful plant that can trick both humans and monarch butterflies, and is contributing to declining monarch populations.
The plight of monarch butterflies is well known. The population of the monarch’s host plant, native milkweed, is diminishing, which makes it difficult for the butterflies to survive. As a result, many gardeners have been planting milkweed to try to help the monarchs. But one type of milkweed that has been advertised as being good for monarchs - tropical milkweed - is in fact a problem for these butterflies.
Before you start planting tropical milkweed seedlings, you need to understand the ways in which this plant upsets the migration of the species.
What's the Difference between Tropical vs. Regular Milkweed?
Not every milkweed species is exactly the same. Tropical milkweed versus native milkweed – exactly what are the differences?
Tropical milkweed (Asclepias curassavica) is an attractive plant, with blossoms and gorgeous green foliage. In mild climates, tropical milkweed doesn’t go dormant. It thrives in spring, summer, fall and winter.
Native milkweed plants, on the other hand, die back after they bloom. They also have flowers and lush leaves, but once winter arrives, they go dormant. This difference proves critical when we consider the relationship of the plants to the butterflies.
The Benefits of Growing Tropical Milkweed in Your Garden
Tropical milkweed is not only an attractive plant, but it is so easy to grow. Compare this to native milkweed which is difficult to propagate. It requires cold stratification of seeds and doesn’t constantly germinate. The tropical variety has impressive blossoms that ornament the garden from June through November, putting on a fabulous display. Tropical milkweed plant care is minimal, and, in warmer areas, it either thrives all year long or returns every year as a perennial.
With all of these benefits, the tropical milkweed plant makes a very good impression on gardeners who want to assist the monarch. You may wonder why you should plant the more difficult native milkweed when this tropical variety is both prettier and easier to take care of. Here’s why.
Gardening tips, videos, info and more delivered right to your inbox!
Sign up for the Gardening Know How newsletter today and receive a free download of our DIY eBook "Bring Your Garden Indoors: 13 DIY Projects For Fall And Winter".
Why Tropical Milkweed is Bad for Monarch Butterflies
But despite all this, tropical milkweed is bad for the monarch population. It interferes with monarch migration and reproduction in several ways.
First, in the north, tropical milkweed grows at the same time of the year as native milkweed. This can confuse the butterflies and make them believe that it is breeding time rather than migration time. For example, in Minnesota, the presence of tropical milkweed prevents monarchs from starting on their normal fall migration to Mexico. While it takes several generations of monarchs to fly north from Mexico, these butterflies fly all the way back to Mexico in one generation. Because this flight requires so much energy, the adults pass into reproductive diapause, meaning that they do not mate. But if the monarchs encounter tropical milkweed, they can break out of their diapause, lay eggs, and stay in the area. When a cold snap comes, the butterflies, caterpillars and eggs will die.
Another problem occurs in mild weather areas where tropical milkweed survives the winters. Monarchs that visit the plants deposit a protozoan parasite called Ophryocystis elektroscirrha (“OE”) on the milkweed leaves. Monarch caterpillars hatching out on the plant eat the leaves together with the OE. Over time, the levels of OE become toxic, which is not true for native milkweed. Although monarchs deposit OE on native milkweed as well, the plant always dies back after flowering, killing off the OE every year. As climate change continues to warm the plant, tropical milkweed may successfully overwinter in more and more locations, enlarging the scope of the OE issue.
Is it Possible to Grow Tropical Milkweed Safely?
There may be safe ways to grow tropical milkweed. This plant can be safely grown in colder-winter areas, since it will die back with the first frost. In warmer areas, gardeners might try growing it in greenhouses. But as the world climate continues to warm, the better, safer option is simply not to plant it and plant native species instead.
Wildlife-Friendly Alternatives to Tropical Milkweed
If you love the look of tropical milkweed but have been convinced not to plant it, don’t worry, there are wildlife-friendly alternatives. If you want a native species that is drought-tolerant, try yarrow (Achillea millifolium). It has lovely yellow, red, pink, or white blossoms. The Zinnia (Zinnia elegans) is another option. It is an annual and there are many cultivars in different colors. Another option is tickseed (Coreopsis), a native perennial with gold and red flowers.
Frequently Asked Questions
Is tropical milkweed invasive?
Yes, tropical milkweed is invasive. It escapes cultivation and establishes in the wild.
Is tropical milkweed a perennial?
Tropical milkweed is a perennial plant in USDA zones 8 - 11, growing as an evergreen in many warm areas. It is an annual in colder zones.
Teo Spengler has been gardening for 30 years. She is a docent at the San Francisco Botanical Garden. Her passion is trees, 250 of which she has planted on her land in France.
-
Beautiful Fall Blooming Shrubs: 7 Flowering Plants For Late Season Interest And Color
While some shrubs fill quiet corners with reliable green tones in autumn, others burst forth with warm, cheerful tones. Try these fall-blooming shrubs for late season hues
By Tonya Barnett
-
Repotting A Thanksgiving Cactus: Your Expert Guide For Thriving Plants
Learn how to repot your Thanksgiving cactus to ensure a happy, healthy houseplant filled with glorious blooms for the holiday season.
By Tonya Barnett
-
How To Grow Native Whorled Milkweed In The Garden
Whorled milkweed is beloved by monarch butterflies, but it attracts other pollinators, too. Click to read more.
By Mary Ellen Ellis
-
Best California Milkweed Varieties For Monarch Butterflies
Click here to learn what the best milkweed varieties for California are.
By Teo Spengler
-
Is Milkweed Plant Poisonous To Pets, People And Livestock?
Butterflies love and depend on milkweed, but the plant is toxic to other animlas. Learn about how to use it responsibly.
By Susan Albert
-
Growing Showy Milkweed From Seed Or Cuttings
Milkweed is a valuable addition to gardens as a magnet for butterflies and other pollinators. Plant it from seed or cuttings, but watch out for the sap.
By Tonya Barnett
-
Milkweed Cutting Propagation: Learn About Rooting Milkweed Cuttings
You may already grow milkweed if you have a butterfly garden. Starting milkweed from cuttings can increase the number of plants you have. For more information, click here.
By Laura Miller
-
How To Grow Balloon Plants: Care Of Balloon Plants In The Garden
Like all members of the milkweed family, the balloon plant is one of the best plants for attracting monarch butterflies. Learn more about adding the balloon plant milkweed species to your garden in this article. Click here for additional information.
By Mary H. Dyer
-
Milkweed Pruning Guide: Do I Deadhead Milkweed Plants
Growing the plants will attract and feed these beautiful butterflies. But you may be asking, “should I prune milkweed.” Milkweed pruning isn’t really necessary, but deadheading milkweed can enhance appearance and encourage further flowering. Click here for more info.
By Bonnie L. Grant
-
No Flowers On Milkweed – Reasons For Milkweed Not Blooming
The sweet nectar of milkweed blooms attracts a wide variety of butterflies, bees, moths and hummingbirds. However, your dream of a garden filled with beautiful winged creatures can quickly become crushed if your milkweed won’t flower. Learn why this happens here.
By Darcy Larum