Notes on Butterfly Plants

We like to see butterflies in our gardens, that is some butterflies, particularly bright, colorful butterflies like the monarch. It’s the caterpillars that we don’t like, the ones that feed on our plants. Luckily for the monarch, the caterpillar stage only feed on weeds, that is, they feed on milkweed, typically common milkweed (Asclepias syriaca), a plant that’s essential to the survival of the monarch butterfly.

It’s not a plant that’s typically grown in suburban gardens, although it would help reduce the decline of the monarch if there was a milkweed plant in every backyard. Since it’s not considered particularly attractive as an ornamental plant, it’s unlikely to happen, but A. syriaca is only one of a number of milkweed species that appeal to the monarch.

In my garden, I have swamp milkweed, which has narrower leaves than common milkweed and grows to about a meter and a half with lots of pink flowers. This species favours medium to wet soils and is well suited to a rain garden or low area, although it wasn’t troubled by last summer’s long dry spell in my garden.

I grew another milkweed species a couple of years back from seed, Asclepias curassavica, a tropical milkweed commonly known as blood flower. This was a pretty plant with showy red/orange flowers and a nice addition to the garden at the time, but it’s not hardy in this area, dying completely over winter. When grown in warmer regions to the south where it can be invasive, questions have been raised about its impact on the monarch. It can act as a host plant, but it’s believed the growth habit of producing new foliage throughout fall and winter can result in continuous breeding on the same plants, ultimately affecting the natural migration patterns of the monarch. They don’t feel the need to leave for Mexico as they should.

There have been calls for eradication of tropical milkweed, but research is still underway to determine the impact of removing a plant that regardless, does provide essential food. Since tropical milkweed can’t survive beyond fall, it’s presumably an acceptable annual plant for our gardens in the north.

Better still, there is another milkweed species we can grow that will attract and feed monarch butterflies. It’s not a major host plant for the monarch larvae, but the flowers provide essential nectar for the adults and it also attracts other butterflies, hence its common name, butterfly weed (can we stop calling them weeds?).

This species is Asclepius tuberosa and like the tropical milkweed, it has similar orange/red flowers. Better still it is hardy to zone 3, making it tough enough to easily survive winter here. Plant in full sun and it will grow in a bushy shape to about knee height. Once established this plant is drought tolerant thanks to a deep taproot. A deep tap root means it isn’t easily moved, so choose carefully when deciding where to place it. This is such a well-respected plant that the Perennial Plant association has chosen it as the 2017 Perennial Plant of the Year.

If you’d like to learn more about attracting monarchs and other butterflies into your garden, there’s an excellent book by local author Thelma Beaubien. It’s called Gardening for Butterflies: Attracting, rescuing and raising butterflies.