Arboretum Paths: Growing Mississippi native milkweeds
Published 7:00 am Wednesday, February 28, 2018
By Patricia R. Drackett, Director and Assistant Extension Professor of Landscape Architecture
The Crosby Arboretum, Mississippi State University Extension Service
This spring is the third year the Crosby Arboretum will be conducting trials of native Mississippi milkweed at the MAFES South Mississippi Branch Experiment Station in Poplarville. The plants will again be trialed in the Crosby Arboretum’s pollinator garden and in area gardens by Pearl River County Master Gardeners.
This year, we will primarily be growing native milkweed from seed collected last year in our coastal Mississippi region. Each year we’ve learned useful information through the trials, so we can better inform local gardeners of the native milkweeds best suited to the conditions of their home landscapes.
For best results, grow milkweed from locally collected seed. However, it can take years to find populations of native milkweed, and to return at the proper time of the year to collect seed. And, it is important to not skip the critical step of subjecting the seed to wet, cold conditions, called “cold stratification”. Even our coastal milkweeds benefit from refrigeration for a minimum of three to four weeks.
At the Poplarville Experiment Station, the milkweed is grown both in field conditions, and in the greenhouse in containers. Surprisingly, some of the species flourished when container-grown, suggesting opportunities for using them in small-scale gardens, for example, on a patio.
The milkweed field trials began in spring 2016 as a result of increased visitor inquiries at the Arboretum the previous spring. They asked about the appropriate native milkweed species for the home garden, in response to widespread media coverage of the previous winter’s record low populations of monarch butterflies overwintering in Mexico.
Gardeners are urged in articles and books to grow their region’s native milkweeds rather than the commonly available, invasive, tropical milkweed (Asclepias curassvica).
However, native milkweeds are not commonly available from commercial growers. And only about a third of the seventy or so species native to the U.S. are considered significant monarch host plants. One of the most widely available native species, butterfly weed (A. tuberosa), is surprisingly not a preferred monarch host plant, as it has unpalatable hairy stems and low concentrations of cardiac glycosides.
Seed of the orange butterfly weed has been available for decades. Varieties include the yellow-blooming variety, ‘Hello Yellow’, and one with a range of colors called ‘Gay Butterflies’.
Wholesale nurseries are reluctant to grow milkweed, even with its recent popularity, due to its attractiveness to insects such as aphids and milkweed beetles. Aphids in particular can be a serious issue as they can be transferred to other plants. Milkweed needs to be grown without pesticides to be a useful host plant for monarch caterpillars. Even small amount of the chemicals can remain in the plants for many months, resulting in the death of feeding caterpillars.
Home gardeners will have the best success growing native milkweeds if they will learn about the species common to their region – their cultural preferences and growing habits. Keep in mind that the milkweed suited to grow in a typical garden bed may not be the best to plant in natural areas.
Just like people, every milkweed species is different. Some may be found in the wild as a single specimen, while others may grow in large groupings. Do you wish to plant native milkweed to fits your environmental conditions, or are you looking to grow it in your garden bed?
The three best performing species in 2017 were Aquatic Milkweed (Asclepias perennis), found locally in the mucky soils and shady areas along rivers and streams, Swamp Milkweed (A. incarnata), suited to sunny garden beds, and Whorled Milkweed (A. verticillata), a colonizing species found in dry fields.
Green Antelopehorn (A. viridis) also colonizes and is found growing in fields in similar, dry conditions.
Monarch caterpillars need to consume a lot of milkweed, so provide large quantities, obviously those species of milkweed that either will colonize or perform well in a regular garden bed.
A poster that illustrates the fifteen most common Mississippi milkweed species, along with a table of their preferred environmental conditions, is available on the Crosby Arboretum website.
Other posters on the website summarize the results of the last two years of trials. Finally, a “Mississippi Milkweeds” Facebook page has been created to help facilitate the exchange of information. Visit soon!
Prescribed fire demonstrations are potentially available at the Arboretum on Thursdays and Fridays from 10:00 a.m. to 2:00 p.m. for the next few weeks, weather permitting.
The Crosby Arboretum is located in Picayune, I-59 Exit 4, at 370 Ridge Road and is open Wednesday through Sunday from 9 AM to 5 PM. For more information, see www.crosbyarboretum.msstate.edu.