Asclepias tuberosa – Butterfly Weed – 2017 Perennial Plant of the Year

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By David Graper

SDSU Extension Horticulture Specialist and Director of McCrory Gardens

With all the ”buzz” about bees and butterflies, why not celebrate an excellent plant known for its ability to support insects and birds and serve as the primary caterpillar food for a beloved North American native butterfly? The Perennial Plant Association is proud to announce Asclepias tuberosa as its 2017 Perennial Plant of the Year.

Hardiness: USDA Zones 4 to 9

Light: Butterfly weed grows best in full sun.

Soil: Grows best in well-drained soils and it is drought tolerant.

Uses: Butterfly weed is a perfect selection for full-sun meadow or prairie gardens as well as formal to semi-formal urban gardens. Flower arrangers may use them as long-lasting cut flowers.

Unique Qualities: Asclepias tuberosa plants are butterfly magnets. Flowers are a nectar source for many butterflies and leaves are a food source for the monarch butterfly caterpillars.

Maintenance: Butterfly weed is subject to no serious insect or disease problems. Deer usually avoid butterfly weed.

Commonly known as butterfly weed, this long-lived and striking perennial is native to the continental United States (except for the northeast) along with the Canadian provinces Ontario and Quebec. With vibrant orange/red/yellow flowers that seem to jump out, butterfly weed is a great addition to a sunny garden with average to dry soils. As the common name suggests, these plants are butterfly magnets.

They also have a medicinal history as treatment for pleurisy, a common ailment in early colonial times, causing wheezing, coughing and great pain due to the inflammation of the pleura round the lungs. Asclepias tuberosa reportedly was so effective in treating this ailment it earned another common name, pleurisy root.

Butterfly weed is a member of the Apocynaceae, or milkweed family. This family includes plants with a milky sap poisonous to most insects. Unlike other milkweeds, Asclepias tuberosa contains little sap. The leaves are 2-5” long, more or less alternate, growing closely together and spiraling up the stem, hairy, un-serrated, lanceolate, sessile or lacking leaf petiole and appearing attached to the stem. Leaves are dark green on top, lighter green beneath. Stems are hairy and branched near the top with flat clusters (umbels) of many showy flowers in late spring through mid-July.

Butterfly weed flowers are easy to recognize because of their “5 up & 5 down” appearance. Each flower has 5 colorful petals that hang down, and 5 upright curved petals called hoods, each possessing one horn. Horns are more or less orange, erect, sickle shaped, inward curved, and formed within the hood. When cross-pollinated a dry fruit forms. This dried fruit, also called a follicle, opens along one side to disperse the seeds. It is 4 to 5” long and only 1⁄2”to 3/4” wide, with a smooth surface. Initially green, they mature brown and split open to release the seeds. Deadheading Asclepias tuberosa is recommended to prevent reseeding, keeping the plants more attractive and promoting a second push of color later in the season. However, the open seed pods are decorative in the fall and winter garden.

Asclepias tuberosa makes excellent, long-lasting cut flowers. Cut stems when more than half the flowers are open; buds do not open well once the stem is cut. Searing the cut end is not necessary to prevent sap from seeping out of the stems. Instead, cut flowers have a good vase life if they are immediately placed in warm water after cutting and either placing stems in a refrigerator for 12 hours or transferring the stems to cold water. This process eliminates what little sap may be produced.

Mature plants do not transplant well so proper siting is important. Young plants develop from a single central stem but with age plants will tiller (develop shoots) at the base, sending up multiple erect stems from a large taproot extending down a foot or more. Due to the taproot, division is difficult but can be done in early spring before new growth begins. Butterfly weed is hardy in zones 4 to 9 and reaches 2 to 3’ high with about a 2’ spread. Don’t cut back in late fall; rather wait until early spring. Mulching young plants prevents frost heaving. Be patient since butterfly weed is slow to emerge in the spring.

Butterfly weed is often grown from seed. Experts report 50-80% germination if fresh cleaned seed is used. If germination does not occur after 3 to 4 weeks provide a 2 to 4-week cooling period. Collected seed will result in flower color variation. To ensure color, purchase seed from a reputable source. Propagation through root cuttings can be used to ensure quality from forms showing merit. Cutting back once, early in growth cycle, will promote compact growth.

Since Asclepias tuberosa is a native prairie plant, butterfly weed is quite comfortable in meadow gardens, native plantings and wildlife sanctuaries but is finding its way into more formal to semi-formal urban gardens. Plant in large masses, for an unrivalled display of eye-popping orange flower color. Butterfly weed pairs well with summer blooming Phlox, Hemerocallis, Liatris, Echinacea, Salvia, and most of June/July sun loving perennials. Another bonus is that deer will leave Asclepias tuberosa alone!

Many bees, wasps, ants, butterflies and beetles visit butterfly weed as well as hummingbirds. All members of the milkweed family serve as larval food for the Monarch butterfly (Danaus plexippus), Queen Butterfly (Danaus gilippus) and the Milkweed Tussock Moth (Euchaetes egle). Let them munch on butterfly weed and you will be rewarded with these “flowers of the air.”

This article was reprinted from the Perennial Plant Association. Visit their website for more information on this and other perennials.

A few other milkweeds to try in your garden

By David Graper

SDSU Extension Horticulture Specialist

Butterfly weed (Asclepias tuberosa) is the 2017 Perennial Plant of the Year, a plant that is certainly deserving of this honor. But there are many other types of milkweeds, additional members of the Apocynaceae family, that a gardener might want to consider adding to their garden as well. There is also a huge diversity of other members of this family that make very interesting house plants.

One of my favorites is another milkweed, native to Great Plains, Asclpeias incarnata, the swamp milkweed. Don’t let the swamp milkweed name discourage you from trying this plant, you do not need a swamp to grow it, since it is a very adaptable plant. While it prefers average moisture conditions, it can tolerate periods of dry weather as well as some occasional standing water. It too is perennial but generally not as long-lived as butterfly weed.

Swamp milkweed grows taller, generally 3 to 4’ in height and does not spread out as much as butterfly weed, usually only about a foot. The flowers are pink and white and are produced mid-summer to fall, mostly at the ends of the upright stems while butterfly weed tends to produce flowers along gently arching stems. Swamp milkweed has a fibrous root system which makes it easier to transplant, but it is very easy to propagate it by seed as well. All sorts of butterflies and bees will flock to the flowers and Monarchs will readily use this plant as a food source for their larva.

Deadheading is recommended to keep the plants from spreading seed around the garden but I like to leave a few, just to keep some fresh new plants growing up. I also think that the opening seed pods are quite attractive as they expose their seeds and little fluffy attachment that allows the seed to be carried a great distance before it settles to the ground. If you end up with too many seedlings next spring, just pull out the ones you do not want or dig them up and share them with a friend. Swamp milkweed grows best in full sun to part shade.

Common milkweed (Asclepias syriaca) was once an abundant plant found in road ditches, fence rows and CRP land across the Midwest and Great Plains. But reductions in CRP acreage as well as the removal of fence rows has dramatically reduced its numbers. Many believe that the marked decrease in Monarch butterflies is directly tied to the reduction in common milkweed populations. Like butterfly weed and swamp milkweed, common milkweed can be utilized in the garden. However, gardeners need to keep an eye on it since it spreads by rhizomes that will allow the plant to spread quite rapidly in the garden, given the chance. Common milkweed has a much coarser texture than the other two milkweeds with leaves that are about 4 to 5” long and about 2 to 3” wide. The stems are also quite large, allowing the plant to grow to 4’ or more. The rounded umbels of pink flowers begin to develop in mid-summer and will continue up until frost. Common milkweed can produce a lot of seed, so once again deadheading is recommended.

Of the three milkweeds, common milkweed probably would best be used in a more naturalized setting that has a bit more of a wild look. Its spreading habit can be troublesome in a more formal setting as new plants pop up from the thick rhizomes beneath the soil, making them a little difficult to manage. But if you had some area at the back of your lot where you could let a few plants “do their thing” the Monarchs and many other nectar-feeding insects would appreciate it.

Another interesting plant to try in your garden, that is also in this family of plants is Gomphocarpus physocarpus. It has many common names including balloonplant, balloon cottonbush, bishop’s balls or my favorite, fuzzy balls. I suspect that you have already gathered from all those common names that the plant produces something that looks like a ball or balloon, which in this case are the fruit, another follicle, similar to what we see in the other milkweeds. In fact, the species name physocarpus means “bladder fruit”.

Gomphocarpus is native to Africa and not hardy in our area, but it makes a great annual plant if you are looking for something that will grow 4 to 5’ tall with a 2 to 3’ spread, attract butterflies, be a food source for Monarch caterpillars and create a point of interest when you invite your gardening friends into your yard. The white flowers begin to appear in late summer and continue into the fall. The fuzzy, round, follicles usually grow to about 2” in diameter and may eventually ripen, split open and release seed if they are not damaged by frost before that time. The fruiting stems may also be cut and used as dried materials for fall bouquets.

There are many other plants related to the milkweeds described here, including members of the sub-family Asclepiadaceae. We see most of these being grown as house plants in our area. Watch for an upcoming article in which I will describe a few of my favorites of those that are easy to grow and have very interesting flowers as well.

Milkweed in bloom. iGrow photo
Swamp milkweed folicles releasing seed. iGrow photo
Swamp milkweed flowers. iGrow photo
Butterfly weed folicles. iGrow photo
Comphocarpus fruit. iGrow photo
Butterfly weed. iGrow photo