Best Practice Tips for Maintaining Milkweed for Monarchs

Best Practice Tips for Maintaining Milkweed for Monarchs

Monarch butterfly caterpillars feed exclusively on milkweed, which Earth Works garden center provides along with best practice tips for maintaining milkweed for Monarchs. As one of the most recognized and beloved of North American native insects, thousands of people provide them habitat and feed them along their migratory path. This is only possible with large amounts of milkweed being available for planting. However, Earth Works also encourages awareness of the benefits of cutting back milkweed in Fall and warm winters to prevent Monarchs from overwintering here rather than joining more healthy populations that migrate back to Mexico.

Monarch Population Decline
Scientists point to a variety of reasons for a decline in Monarch populations, including deforestation, changing agricultural practices, weather extremes, unregulated eco-tourism, fire, and disease.

The good news is that our efforts at providing food and habitat help.
“It is likely that monarch numbers would be even lower without the efforts of dedicated individuals throughout North America, but current numbers show us that we need to increase our efforts,” according to Karen Oberhauser, UW-Madison Arboretum.


monarch butterfly
MBBR Monarch Chart

How the Monarchs are Counted
Monarch population numbers have been assessed yearly since 1994 at the Monarch Butterfly Biosphere Reserve (MBBR) of the National Commission of Protected Natural Areas (CONANP) in Mexico.
Scientists at the MBBR estimate Monarch numbers based on the amount of land the butterflies are roosting on each winter. Since the Mexican overwintering count began, the population estimate of Mexican overwintering Monarchs peaked at one billion in 1996, with the lowest count being 20 million in 2013/2014.


The population numbers have bounced up and down, but mostly down. For instance, the Mexican overwintering Monarch population estimate was up 35% for Winter 2021/2022, but down 26% the prior year. “Scientists estimate that at least 6 hectares is necessary for a sustainable population of eastern monarchs,” according to Monarch Joint Venture. Monarch populations have only met that threshold for sustainability approximately four times in the past twenty years. However, there are growing numbers of Monarchs overwintering in North America that has proved to be unhealthy for them.

Monarchs Milkweed Choices and Preferences
Even though there are over 100 native milkweed species in North America, we are typically only able to supply one or two native species, such as Swamp milkweed, Asclepius perennis due to a lack of commercial growers. The most commonly available species is the Mexican Tropical Milkweed, Asclepias curassavica, as it’s easy to propagate and fast-growing. We encourage homeowners maintaining milkweed for monarchs to provide as much diversity of milkweed species as possible.

A 2018 USDA-funded study found that Monarchs will lay more eggs where they have more milkweed species choices. “It is important to note that monarchs use multiple different milkweed hosts each year throughout their annual cycle,” according to Ecosphere. “Although these milkweed species appear on the landscape in different proportions, monarchs do not specialize on one milkweed species even when both have co-evolved within a smaller region (e.g., eastern vs. western North America). Monarchs from both the eastern and western populations exhibited the same oviposition preferences when given access to milkweed species from both eastern and western North America.”

Mexican Tropical Milkweed
monarch caterpillar

Milkweed Routine Maintenance in the Fall
Native North American milkweed species are more likely to die back in Fall than the Mexican Tropical Milkweed variety that, during warm winters, can continue to produce foliage and blooms.
“Jim Edson, a geology professor at the University of Arkansas, said, “one research project offered five kinds of milkweed to monarchs,” according to the Arkansas Democrat Gazette. “Butterfly weed was least liked and tropical was preferred. But scientists fear that what the monarchs like the most may be bad for them.”

Since the Monarchs enjoy Mexican Tropical milkweed found here, it’s become challenging to get them to migrate back to Mexico. Scientists are concerned that the suitable areas where Tropical milkweed can survive the winter from the Carolinas to California keep Monarchs here year-round. The problem with this is that Monarch populations that don’t return to Mexico have higher infection rates of the naturally occurring protozoan Ophryocystis elektroscirrha (OE), which causes deformities and death.

Rate of Infection & Impacts
According to a University of Georgia study, in the wild, in the western US, about 30% of all wild Monarch butterflies have HEAVY OE spore loads,” wrote Butterfly Fun Facts. “In the eastern US, less than 8% of Monarch butterflies have a HEAVY spore load. In the southern tip of Florida, where Monarchs fly and lay eggs all year, more than 70% have HEAVY OE. Experts estimate that nearly 100% of wild Monarchs in the Miami/Dade area of Florida are infected with OE, from mild to heavy infection. If OE was super deadly in the wild, the southern tip of Florida would not continue to have a large population of Monarch butterflies.”

overwintering locations for monarchs in north america

Scientists Are Seeking Solutions
And although infected Monarchs can spread OE’s spores via any milkweed species, there is still little progress in finding a cure, although, for those rearing them, there are recommendations for reducing the spread. “We have worked out a way to control this parasite that we hope will not be too difficult,” according to Scientists at “Our method requires cleaning up your rearing operation; we have not yet found a way to “cure” a larva once it has eaten the spores, although at the University of Kansas we are continuing to look for such a solution using drugs that have been shown to work on related organisms. We have had limited success with attempts to surface-decontaminate eggs once they have been laid, although this does lower the incidence of the disease. Thus, the only way to solve the problem, and to prevent more releases of contaminated butterflies, is to make sure that the larvae you rear are never exposed to the parasite. There are four steps you will need to take. ” Learn more at Monarch Watch.

Scientists have found OE to be transmitted in three ways: infected females spreading spores onto their eggs, by contact with milkweed that infects others Monarchs, and during mating. “Monarchs that acquire spores as adults are temporary carriers, and themselves do not experience detrimental effects of the parasite,” according to their research published at the National Library of Medicine.

monarch Lifecycle source USDA

We at Earth Works hope this information benefits your understanding of best practices for maintaining milkweed for monarchs. Visit our garden center and speak to staff about the availability of milkweed and the many nectar plants available for them and other pollinators in Northeast Florida.

Happy Gardening!

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