The Asclepias genus, a group of herbaceous plants, is well documented in North America. Over 100 species grow in disturbed habitats such as agricultural areas and roadsides. However, not all of these species are desirable plants for the garden. Two attractive species that grow well in gardens are Asclepias curassavica (tropical milkweed) and A. tuberosa (orange butterfly weed). Orange butterfly weed is native to the United States and is hardy in USDA Zones 3-9, while tropical milkweed is native to South America and is hardy in Zones 9-11. The thumbnail photograph on the right depicts tropical milkweed.
The Plight of the Monarchs
Gardeners know that the monarch population is in serious decline. To begin with, some of the forest the monarchs depend on for overwintering in Mexico has been cut for timber. Bad weather, spring droughts, dwindling supplies of wild milkweed, and other factors also contribute to the decline. Urban and suburban spread, genetically modified and herbicide tolerant crops, along with widespread pesticide use have caused the loss of an estimated 2.2 million acres of potential milkweed habitat according to Monarch Watch. In addition, the parasite Ophryocystis elektroscirrha (OE) infects a significant number of the monarch population with deleterious effects.
Gardeners as a group are aware of the plight of the monarchs, and we try to help. We head out to the nearest nursery and purchase whatever milkweed is available. Most likely we will find Asclepias curassavica or tropical milkweed. This milkweed is easy to grow, and its fibrous root system grows well in containers and transplants readily. Tropical milkweed is showy in our gardens, and it attracts monarchs as well as the native milkweeds. While it is perennial in Zones 9-11, gardeners north of these zones grow it as an annual.
Native Butterfly Weed
Well established patches of native butterfly weed are treasures. Gardeners lucky enough to have a few established clumps of Asclepias tuberosa already know that it lasts for years and becomes thicker and showier every year. It’s the “getting it established” that presents the difficulty. While A. tuberosa is not necessarily hard to start from seed, it is best planted where it is to grow and left alone except for thinning out seedlings if too many sprout. Plants started from seed take two to three years to produce flowers, and they do not transplant well.
Native orange butterfly weed (Asclepias tuberosa), on the other hand, can seldom be found in garden centers. To begin with, it takes two or three years for the plants to flower when started from seed. Nurserymen are often unwilling to invest time in a plant that takes so long to become sellable. In addition, a long tap root makes it hard to grow and hold in containers for an extended time. Below are three photographs of Asclepias tuberosa. Mouse over the pictures for specific identification or cultivar names.
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By the time the plants bloom, they should be well established, and the patient gardener who took the time and made the effort to grow these plants from seed can sit back and enjoy the results of their efforts and rest assured they have contributed to the monarch butterflies in a positive way. Butterfly weed will flourish in poor, dry soils, so it is an excellent choice for gardeners with well-drained soil who do not relish watering plants frequently. Asclepias tuberosa is hardy in Zones 3-9, so it can be grown throughout the United States and parts of Canada on favorable sites.
My next article for Dave’s Garden will discuss this topic in more detail. Much controversy exists in the arguments about which milkweed to select for your garden. Even the experts present opposing opinions. It is a topic deserving serious investigation by the experts in the field and close study of their results by everyone. All of us have the monarchs in mind and want them to continue to grace our planet. Let’s resolve to find answers to complex problems and work toward solutions—for ourselves, our planet, and for the butterflies.
Other articles about milkweed on Dave's Garden include "Got Milkweed? -- Attracting Monarch Butterflies to Your Landscape" by Mrs_Ed and "Milkweeds: Which one's for your garden?" by Sallyg. Both are informative and have additional information about milkweed and monarchs.
Thank you to Gabrielle for her photographs of 'Gay Butterflies' and Asclepias tuberosa and to Aphthona for the photograph of 'Hello Yellow'.