Butterfly Garden Plant Profile: Milkweeds

I thought I would try something new, and start profiling each of the plants (or plant groups) in my butterfly garden as a complement to some of the more macro-level discussions I started with. There seems to be no better place to start than with the milkweeds (Asclepias sp.) Plants of this genus are the only hosts for North America’s most iconic butterfly, the monarch. They also attract a wide variety of other insects, for a variety of reasons. Several species are native to the mid-Atlantic, and a few others grow well here. I haven’t found any of these on lists of invasives, so I have chosen to include a sampling of both native and non-native species in my garden. I can confirm anecdotally that monarchs will readily use all as host plants and that many species will take nectar from the natives and non-natives alike.

IMG_4139
common milkweed

Common milkweed (A. syriaca) is a native plant with lovely spheroid clusters of white-and-pink flowers. It can grow 5-6 feet (or more?) tall in good conditions. This is one of the first plants I started in my garden for perhaps obvious reasons. I have seen it in action hosting monarchs, milkweed tiger moths, swamp milkweed leaf beetles, small and large milkweed bugs, red milkweed beetles, and more. Seemingly every pollinator will make a stop at the flowers. It is fairly easy to grow from seed, especially if cold-stratified first. It seems to handle relocation well. This plant will thrive in moist but well-drained soils, but in my experience it will tolerate most conditions. I am always nervous about cutting back plants mid-season, but because monarchs prefer young leaves and breed in Maryland later than milkweeds emerge it is good practice to do so. The milkweeds can handle it.

IMG_4670
swamp milkweed (amid some partridge pea)

Swamp milkweed (A. incarnata) is quite similar. As its name suggests, it does prefer things a little bit wetter. Mine hasn’t taken off quite as well as the common milkweed, but it does return each year. Its flower clusters are smaller and not the same near-spherical shape, but do tend to a brighter pink. The leaves and seed pods are narrower. Other than the wetness, the same plant care notes apply to swamp milkweed. I know it hosts monarchs and the swamp milkweed leaf beetle and I suspect the other insects mentioned above can eat it as well. It’s a great alternative to common milkweed for a wetter space.

Asclepias tuberosa
butterfly weed (with oleander aphid infestation)

I am still trying to establish some butterfly weed (A. tuberosa). I had read that this species can take a little longer than the others to get going, and this is proving true. Butterfly weed has bright orange flowers and clear (as opposed to milky) sap. So far none of my seedlings from previous years has survived – I don’t know if I have been choosing the wrong location, experiencing a run of bad luck, or something else, but I will keep trying. The orange would really be a nice accent to the rest of my garden’s color pallette. It’s also reportedly a great nectar plant for many pollinators, and since biodiversity is my ultimate goal any native plant that fits the host/nectar profile is a plant I want.

The Maryland Biodiversity Project lists nine additional species (plus two subspecies of swamp milkweed) as Maryland natives. Some appear to be quite rare, and others are limited to the coastal plain. The remaining few species are on my list of potentials for future plantings – clasping milkweed (A. amplexicaulis) looks particularly attractive. I’ll have to balance diversifying the milkweeds with filling other niches, though, so they may have to wait in queue for a few years.

I did mention non-natives, and thus far I have tried two of these. Last year I added some bloodflower (A. curassavica), a more southern species that nonetheless grows well here.  I couldn’t resist the striking red-and-yellow flowers or the glossier green of the stems and leaves. I have observed monarch caterpillars munching on this plant and many insects taking its nectar, so I feel vindicated in sneaking in this non-native plant for variety’s sake. This year I am similarly experimenting with “showy” milkweed (A. speciosa), which is from the western half of the continent. I’m not sure if the seedlings survived the deluge we got earlier this month, but if they did I look forward to seeing if these perform as well as the bloodflower.

IMG_4682
Bloodflower

I haven’t had too many problems keeping milkweeds healthy once they’re established. One exception is the occasional infestation of oleander aphids. Perhaps coincidentally they have attacked my swamp milkweed most voraciously. The point of my garden is of course exploitation by animal life, but this non-native aphid does not contribute positively to the ecosystem so I don’t tolerate them. Fortunately they seem fairly easy to control. I have found manual removal to be very effective. I simply squish them by grasping the plant stems and rubbing, then rinse the gross yellow goo with a hose.

IMG_4520

All in all, milkweeds are low-maintenance flowers that add a lot of visual interest to a garden. They check a lot of boxes in terms of ecological niches as well, even excluding their well-documented relationship with monarch butterflies. There’s very little not to like.

Intro to Butterfly Gardens

Planting a butterfly garden was one of my first landscaping priorities after moving into my home in 2014. On one level, this was motivated by the idea that butterflies are pretty, and it would therefore be cool to see a lot of them often. This is true, and a perfectly fine motivation, but “butterfly garden” is a bit of a misnomer, at least in terms of the endgame. Butterflies (and the other pollinators attracted to the same plants) are hugely important to the ecosystem. Butterfly larvae are a major food source for birds and small mammals – some birds feed almost exclusively on caterpillars of a single species. Increasing local butterfly diversity and population will thus increase the local overall biodiversity and biomass, and sometimes dramatically. It doesn’t have quite the same ring, but I like to think of my garden as a “biodiversity garden.” Some call them “native plant gardens,” or a similar variant. whatever the term, the idea is to support the ecosystem by planting plants that have naturally evolved with other life in the area over millennia.

img_2228
About half of my butterfly garden as of this July.

Designing a butterfly garden, as any garden, begins with deciding what you wish to plant. The goal here is to include mostly native plants that will attract butterflies (and moths and skippers – I probably should be saying “lepidopterans”). Butterflies rely on plants for food during both active stages of their life cycle: the adults feed on nectar and the caterpillars feed on leaves. Like humans, the young of butterflies can range from not picky (generalist) to extremely picky (specialist) eaters. The monarch is the classic example of a specialist – its caterpillars will only feed on milkweeds (Asclepias species). Plants a given species will eat are called “host plants” for the species, and females will only lay their eggs on suitable plants. Adults are typically much more cosmopolitan in their tastes, but feed on nectar. A successful butterfly garden will feature nectar plants to attract the butterflies and host plants to keep them there and propagate them. Of course, many plants serve both purposes, making them ideal choices.

img_2590
Two monarch caterpillars on a common milkweed leaf.

There seems to be some debate regarding the ideal ratio of host plants to nectar plants. My beginner’s take is that it probably doesn’t matter much as long as both are present in significant quantities. However, the more limited the space the more selective one must be. I have hedged my bets a bit by planting as many plants as possible which fill both roles and building around those. Additionally, it’s helpful to consider what is planted elsewhere in your yard and immediate neighborhood. Butterflies after all will not recognize the boundaries of your garden or your property, so plants nearby can also contribute. Many trees and shrubs which may not be practical fits in your butterfly garden space are host plants for a diverse mixture of butterflies and moths. Most common oaks, for example, host hundreds of caterpillar species. Spicebush (Lindera benzoin) is a host plant for the appropriately named spicebush swallowtail. Viburnums host many species and produce lovely white flower clusters.

Aside from plants, a number of other things can encourage butterflies to visit your garden or extend their stay. Many butterflies will feed on overripe fruit, so a suspended tray of fruit can be a nice feature. Some feeders include a sponge soaked in sugary water as well. Butterflies also engage in a behavior called “puddling” to soak up nutrients from wet soil, and providing them with a space to do so can entice them to hang around longer. You can purchase a puddler or make your own, or simply rely on mud puddles. Butterfly houses can also be bought or built as encouragement for your visitors to hang around. Rock piles and/or log piles can serve a similar function (providing shelter from weather and predators). It’s also a good idea to add a place for humans to sit and observe the wildlife; I built a bench from (mostly) natural wood for this purpose.

img_2871
Caterpillars of the milkweed tussock moth

Much of the source material I turned to when planning my butterfly garden focused pretty extensively on monarchs and milkweeds. It led me to wonder why monarchs in particular get so much of the butterfly press, but the more I think about it the more it makes sense. Monarchs are beautiful, large butterflies that are well known. Because of the viceroy, they’re part of the definitive example of Batesian mimicry. They are also in trouble because milkweeds are in trouble. As I’ve mentioned, their larvae will only eat milkweeds. As one might infer from the name, these plants have long been regarded as, well, weeds. People have been systematically removing milkweeds from a lot of areas, unwittingly endangering monarchs in the process. It isn’t just a problem for monarchs, though. The milkweed tussock moth, small and large milkweed bugs, red milkweed beetle, and other insects all rely heavily on Asclepias. The relationship between milkweeds and monarchs is a very illustrative example, but far from the only example. Adult butterflies will feed on the nectar of non-native flowers, but virtually no non-native plant can host a native caterpillar.

img_2586
Nymphs of the large milkweed bug clustering on a seed pod
img_2047
Red milkweed beetles on – you guessed it – milkweed!

 

 

 

 

 

 

 

This returns me to the butterfly garden’s true purpose: to contribute ecological functions to the local biosphere. The native host and nectar plants have evolved relationships with many local forms of life on a grand time scale. Restoring these plants to an area also restores those relationships. Alien plants can stand in and provide some of the ecological functions, but not nearly all. I won’t advocate for the complete removal of all non-natives from gardens and other home landscaping, and I make concessions in this area myself. Increasing the number and variety of native plants in one’s yard, though, is a noble goal and a butterfly garden provides an excellent framework for doing so.

 

img_2849
A pair of eastern tailed-blues on a New England aster

Further Reading:

North American Butterfly Association

Our Habitat Garden

The Butterfly Website

Bringing Nature Home