In North America, the serious decline of the monarch butterfly (Danaus plexippus), the black-veined orange migratory butterfly that winters in Mexico and California and travels all the way to Canada in the summer, has been highly publicized. It’s hard to imagine of anyone who hasn’t heard about it. Its population has been declining for at least 50 years, and since 2008, the population has dropped dramatically, from 1 billion to 93 million butterflies. That still sounds like a lot of butterflies, but if the population keeps dropping at this rate, within a generation this emblematic butterfly will no longer grace our fields and gardens.
Several authorities attribute the decline to modern agricultural practices, especially the widespread use of herbicides (deadly to milkweeds, the unique food of monarch caterpillars), as they create vast surfaces where nothing but the crop in question (maize, soybeans, etc.) grows. Monocultures stretching as far as the eye see offer neither food nor shelter to migrating monarchs.
In addition, several years of climate disruption in Texas, a state through which almost all the monarchs in eastern America have to pass, including severe droughts and unseasonable frosts, have aggravated the situation. As have the illegal cutting of forests in Mexico where the butterflies spend several months in winter dormancy and the indiscriminate use of insecticides everywhere along their route.
In recent years, associations have appeared throughout North America that seek to protect monarch butterflies. Most have developed some sort of program that asks home gardeners to “do their share” and offer an oasis for monarchs on their lot: a garden often called a monarch way station, somewhere monarch butterflies will not only be tolerated, but actually encouraged.
The principle is certainly simple enough: monarch butterflies need flowers in order to survive, so if enough people create flower beds all along the route that butterflies follow from Mexico to southern Canada, that should help the monarch population to recover!
Especially put forward is the idea of planting milkweeds (Asclepias spp.). Indeed, monarch larvae (caterpillars) can only feed on milkweeds (and plants of the related African genus Gomphocarpus): they have no other source of food. They’ll die if offered anything else. Plant a milkweed, save a butterfly: it certainly sounds simple enough.
No Sooner Said Than Done!
Gardeners definitely understood the last point. They are planting more milkweeds. The sale of milkweeds, once rather obscure plants, is booming in Canada and the United States: everybody seems to be planting them, notably with school teachers pushing the idea in the classroom and kids asking their parents to plant them … and that’s great. Every little effort helps. But planting milkweeds is not going to entirely solve the problem: it’s a bit more complicated than that.
Just as important as planting milkweeds to feed larvae is planting and maintaining nectar plants for adult butterflies. Adult monarchs, in fact, are not in any way limited to milkweed flowers, but instead feed on a wide range of nectar-rich blooms. They need plants in bloom as a food source whenever they’re in a given region. That is, from spring through late fall in the south and in the summer and very early fall in the northern part of their range.
Storing Up for the Return Trip
It is especially important to offer an abundance of nectar-rich flowers in late summer and in fall. Here’s why:
Contrary to their spring migration, which is multi-generational (monarchs migrate in stages, stopping on their way north to lay eggs at different points and produce new butterflies that will complete the route to the North, and therefore milkweeds are essential for feeding the caterpillars of the up-and-coming generation), the return from the North to the South is done in a single generation. The same butterfly born in the summer on a milkweed in, say, Northern Ontario, at the extreme northern edge of the monarch’s range, has to fly all the way to the heart of Mexico, a distance of about 3,000 miles (4,800 kilometers). Before it leaves, at summer’s end, it needs to stock up on lipids (fats) that will help carry it down to Mexico. Then all along its route south, it needs to stop regularly to feed on flowers rich in nectar.
Note that milkweeds (Asclepias) are not at all necessary on the return trip and at any rate, most will have finished blooming by then. Monarchs don’t need milkweeds in the fall, because the females will not be laying eggs on their way south, nor will there be any caterpillars that need to feed on milkweed leaves. Actually, it won’t be until March or April of the following year, when monarch butterflies wake up after their winter dormancy and start to fly north, that they need to find milkweeds on which to lay their eggs. Instead, southward migrating monarchs need other nectar-rich flowers: late-blooming ones.
This is such an important factor that some scientists believe that to try to boost the monarch population, planting milkweeds is considerably less important than preserving and planting late-blooming flowering plants! (See the study done by Cornell University: Linking the continental migratory cycle of the monarch butterfly to understand its population decline.)
Create Your Own Monarch Oasis
If you want to create a monarch garden on your lot or organize one at your school or in a local park, here are some considerations:
- Ideally, it should be in full sun in a spot protected from the wind.
- It should contain milkweeds (Asclepias spp.) to feed the caterpillars in the spring (southern locations) and in early to mid-summer (elsewhere), as well as a good variety of nectar-bearing flowers to feed the adult butterflies throughout the summer and into fall.
- The larger the flower bed, the more it will be used. (Do you really need the vast sea of green lawn that surrounds most houses and that is the equivalent of a monarch butterfly desert?)
- You have to learn to accept a bit of imperfection in a butterfly garden. Yes, some leaves will be munched on: the caterpillars need to eat something! And there will probably be less attractive insects on your milkweeds (they do have their share of insect pests) you’d do best to learn to ignore.
- Avoid treating your butterfly garden with products toxic to butterflies, such as insecticides. If you feel you have to treat plants in the garden, prefer gentle treatments like a sharp spray of water or hand picking. Even organic insecticides, likes insecticidal soap and neem, can harm caterpillars and butterflies.
Plants That Feed Monarchs
To feed monarch caterpillars, it’s essential to include milkweeds in your monarch oasis.
Butterfly weed (A. tuberosa), zone 4, with orange or yellow flowers, and swamp milkweed (A. incarnata), zone 3, with pink or white flowers, are the easiest to find in plant nurseries. The first prefers very well-drained to dry soils, while the second is better adapted to average garden soils, which are richer and more humid.
In eastern North America, common milkweed (A. syriaca) is already widespread in the wild, as is its western equivalent, showy milkweed (A. speciosa), in its territory. Neither are widely available commercially and can be a bit invasive in a flower bed.
Gardeners in mild climates and those limited to balcony and patio gardening could try tropical milkweed (A. curassavica). It will grow as a perennial in zones 9 to 11 and in pots as an annual in colder climates.
There are some 140 other milkweed species, but the commercial distribution of most is very limited.
So, you’ve planted milkweeds to feed monarch caterpillars. Now you have to nourish the adult butterflies. For that, you need a good variety of plants that produce abundant nectar. Milkweeds do work, but likely won’t be enough. You need plenty of flowers of all kinds.
Butterfly plants usually produce inflorescences with clustered flowers, such as are found in the Asteraceae, Apiaceae and Verbenaceae families. Either loose clusters, like lantanas or verbenas, or dense flower heads, like rudbeckias and echinaceas, will do. The latter even come with a butterfly landing platform, the ray flowers (their so-called petals) that surround the flower head. Butterflies generally find individual flowers less attractive.
Brightly colored flowers attract monarchs, but they are relatively indifferent to perfumes (except for the fragrance of milkweeds, which they can detect from a great distance). Beware of double flowers: sometimes, but not always, the extra petioles render the nectar inaccessible to monarchs.
The traditional belief that you should choose strictly native flowers for your monarch oasis is now considered erroneous: recent studies show that a mixture of native and imported flowers attracts and feeds the most butterflies.
At the end of the summer, things start to get serious. Monarchs will need to drink a lot of nectar to accumulate good reserves, essential for their flight south. Thus, the utility of nectar-rich flowers increases as summer winds down. The list below concentrates on plants that will be in bloom from mid-August on, the time of year when monarchs need nectar the most:
- Ageratum (Ageratum spp.) — annual
- Ageratum, Hardy (Conoclinium spp.) — zones 5–10
- Alyssum (Lobularia × hybridum) — annual or zones 9–11
- Aster (Aster spp., Symphyotrichum spp. and several other genera) — zones 2–9
- Balloon Plant (Gomphocarpus spp.) — annual or zones 10–11
- Bergamot, Wild (Monarda fistulosa) — zones 3–9
- Black-eyed Susan (Rudbeckia spp.) — zones 3–9
- Blanket Flower (Gaillardia spp.) — annual or zones 3–10
- Blazing Star (Liatris spp.) — zones 3–8
- Bluebeard (Caryopteris spp.) — zones 5–9
- Boltonia (Boltonia spp.) zones 3–8
- Boneset (Eupatorium spp.) — zones 3–9
- Bottlebrush (Callistemon spp.) — zones 9–11
- Butterfly Bush (Buddleia spp.) — zones 6–9
- Buttonbush (Cephalanthus occidentalis) — zones 4–10
- Catmint (Nepeta spp.) — zones 3–9
- Celosia (Celosia spp.) – annual or zones 10–11
- Chives, Garlic (Allium tuberosum) — zones 3–8
- Cockscomb (Celosia argentea cristata) — annual or zones 10–11
- Coneflower (Echinacea spp.) — zones 3–9
- Coreopsis (Coreopsis spp.) — zones 3–9
- Cosmos (Cosmos spp,) — annual
- Crownbeard (Verbesina spp.) – zones 4–8
- Culver’s Root (Veronicastrum spp.) — zones 3–9
- Dahlia (Dahlia × hortensis) — annual
- Dewdrops, Golden (Duranta spp.) — zones 9–11
- Echinacea (Echinacea spp.) — zones 3–9
- Flame Vine (Pseudogynoxys chenopodioides, syn. Senecio confusus) — annual or zones 10–11
- Gaillardia (Gaillardia spp.) — annual or zones 3–10
- Giant hyssop (Agastache spp.) — zones 2–10, according to species
- Globeflower (Gomphrena spp.) —annual
- Goldenrod (Solidago spp.) — zones 3–9
- Heliotrope (Heliotropium arborescens) – annual or zones 9-11
- Hempvine, Climbing (Mikania scandens) — zones 6–9
- Ironweed (Vernonia spp.) – zones 4–9
- Joe-Pye Weed (Eutrochium, formerly Eupatorium spp.) — zones 3–9
- Lantana (Lantana spp.) — annual or zones 9–11
- Marigold (Tagetes spp.) — annual
- Milkweed (Asclepias spp.) — zones 3–10
- Mint, Moutain (Pycnanthemum spp.) — zones 4–8
- Mistflower (Conoclinium spp.) — zones 5–10
- Phlox, Garden (Phlox paniculata) — zones 3–8
- Porterweed (Stachytarpheta spp.) — annual or zones 9–11
- Rose (Rosa spp., varieties with single flowers) — zones 3–10
- Rosinweed (Silphium spp.) — zones 4–8
- Rudbeckia (Rudbeckia spp.) — zones 3–9
- Sage (Salvia spp.) — annual or zones 5–11
- Sage, Russian (Perovskia spp.) — zones 4b-9
- Sedum (Sedum spp. et Hylotelephium spp.) — zones 3–9
- Spirea, Blue (Caryopteris spp.) — zones 5–9
- Spirea (Spiraea spp.) — zones 3–8
- Star Flower, Egyptian (Pentas lanceolata) — annual or zones 9–11
- Sunflower (Helianthus annua) — annual
- Sunflower, Mexican (Tithonia rotundifolia) — annual
- Thoroughwort (Eupatorium spp.) — zones 3–9
- Tickseed (Coreopsis spp.) — zones 3–9
- Verbena, Garden (Verbena x hybrida) — annual or zones 9–10
- Verbena, Rose (Glandularia canadensis) — annual or zones 6–9
- Verbena, Tall (Verbena bonariensis) — annual or zones 7–9
- Yarrow (Achillea spp.) – zones 3-9, according to species
- Zinnia (Zinnia spp.) — annual
Do your bit to save monarch butterflies: plant a flower garden!