Dr. Leonard Perry, Horticulture Professor Emeritus
University of Vermont
Milkweeds have many benefits—they are hardy, low maintenance, good in rain gardens as well as in dry soils and during droughts, tolerate deer, the mid-summer flowers attract butterflies and the leaves feed monarch butterfly larvae.
Milkweeds are not weeds at all (a plant out of place that you
don’t want in your garden) unless, perhaps, you have a formal
garden. The common milkweed (Asclepias syriaca) is perhaps
the most common colonizer of gardens and farm fields. In the
latter, this native plant can be a problem, being toxic to grazing
animals and poultry when eaten in quantity. Its cardiac
glycosides make it toxic to humans too but, due to the milky sap,
it isn’t often eaten. Most milkweeds have some toxicity, but it
varies with species.
Native Americans used native species of this plant for a range of
medicinal uses, and taught colonists how to cook and prepare it
properly so not to be poisoned. Uses ranged from skin warts and
snake bites to digestive problems, fevers, sore muscles and its
main use—lung conditions such as asthma, bronchitis and pleurisy
(from whence it gets the common name “pleurisy root”). In fact,
its scientific genus name (Asclepias) honors the Greek god
of healing, Asclepius.
With increased recent interest in pollinators, milkweeds have
gained more recognition as important to a range of pollinators and
particularly to the threatened monarch butterfly. Butterflies
feed on the flowers, but milkweeds are the sole food for their
larvae. The same toxic properties that may harm humans and cattle
protect monarch larvae. By ingesting milkweed leaves, they in
turn become toxic to birds and other predators, so are left alone.
Milkweeds are a plant that, like orchids, has evolved a rather
unique and complex pollination strategy. The pollen is contained
in pollen sacs (“pollinia”) which attach to pollinators when their
feet or mouthparts slip into slits between anther flower parts.
These pollen sacs are then carried to another flower where they
get lodged into similar flower slits. Although the monarch is
most associated with milkweeds, it isn’t one of the most effective
Milkweed flowers are grouped into domed, slightly drooping
clusters (“umbels”) which arise from where upper leaves join
stems. Colors vary with species, but are generally pink, white,
or orange. Depending on region and species, they may bloom from
spring through summer on plants ranging from one to five feet
The flowers eventually produce warty elongated seed pods
(“follicles”), two to four inches long, which turn from green to
tan when ripe and split open. They release many seeds with silky
tails (“coma”), often called floss or silk, which aid in wind
dispersal. This floss often has been used in stuffing pillows, as
insulation for coats, as acoustic insulation, and oil absorbents.
Pods can be harvested and used in decorations naturally, or
Milkweeds grow best in full sun, blooming less and being more
leggy in part shade. Most native species are hardy to USDA zones
3 (minus 30 degrees average winter minimum). They are slow to
emerge in the spring, so require patience and careful attention to
early season gardening around them.
They prefer medium to dry soils, tolerating rocky and poor soils,
except the rose or swamp milkweed (A. incarnata) which
prefers medium to wet soils. Those species that tolerate drought,
once established, do so through deep tap roots. These roots make
most milkweeds difficult to transplant, so place them properly
when planting. If they must be moved, do so when plants are
Flowers are showy, fragrant in some species, and can be used
cut. Plants are useful massed in natural and native plant
gardens, as well as gardens for pollinators, and some species in
rain gardens. In addition to all these benefits, and their low
maintenance with few problems, is their resistance to deer
Milkweeds used to be in their own family, but are now grouped in
the dogbane family (Apocynaceae). There are over 140 species, of
which at least half are native to eastern North America. Most are
rather rare or seldom seen, but there are a handful that are sold
for garden use.
The butterfly weed (A. tuberosa), or orange milkweed, is
the most common species that most know. It has orange flowers in
mid to late summer, eventually reaching about two feet tall and
wide with an open upright habit. Leaves lining the stems are
stiff, long and narrow. With its attractive flowers and all the
other usual milkweed benefits, it was named the Perennial Plant of
the Year in 2017. ‘Gay Butterflies’ is a mix of yellow-, orange-,
and red-flowering plants.
You may find a yellow-flowered cultivar (cultivated variety) of
butterfly weed called ‘Hello Yellow’. In her graduate study in
Vermont, Annie White found that over 90 percent of pollinator
visits to either this cultivar or the species were by bumblebees.
There was a small, but not very significant, preference with
pollinators for the species over this yellow cultivar.
The swamp milkweed, as noted already, prefers more moist soils so
would be good for such sites where many perennials don’t grow
well. This makes it a good candidate, too, for rain gardens and
clay soils. It can grow three to four feet high, and about half
as wide. Flowers in late summer are in pink, white, and mauve.
Common cultivars are ‘Cinderella’ with larger rosy pink flowers,
‘Ice Ballet’ with white flowers, and ‘Soulmate’ with rose-purple
The common milkweed, as noted, is one that colonizes in the
wild—fields, along roads and ditches, and even into natural
gardens. The stout, upright stems reach three to four feet, and
hold pinkish purple flowers from mid through late summer.
A milkweed that isn’t native but is quite colorful with red and
orange flowers, and so is often seen for sale, is the blood flower
or tropical milkweed (A. curassavica). It is native to
South America, so only hardy to subtropical USDA zone 9 regions
where it often self-sows and becomes weedy. In most areas it is
grown as a well-behaved annual flower, getting two to three feet
high, and with blooms through the season. This milkweed is
attractive to hummingbirds.
If you aren’t already growing milkweeds, or would like to add
more, you can start them from readily-available seeds. This may
take some time, but will be cheaper for producing many plants.
Quicker is to buy plants from nurseries.
Return to Perry's Perennial Pages: Green Mountain Gardener Articles-- your reliable source of gardening information for over 50 years.