Adult monarchs don't eat flowers but drink liquid nectar, a sugary substance made by flowers. The monarch butterfly--like other butterflies--is built to drink liquids. Its mouth, called a proboscis, is a straw-like pipe, which is kept coiled until the butterfly is ready to eat. The proboscis allows monarch butterflies to reach liquid nectar kept deep in a flower's center. Monarchs are the only butterfly in North America to migrate to warmer climates in the fall.
Although adult monarchs drink the nectar from almost any flower, the milkweed plant (Asclepias) is necessary for it's larvae. In fact, without milkweed, larvae would not be able to develop into adults. According to the U.S. Forest Service, monarchs use a variety of milkweed species as hosts for their larvae, but are attracted to milkweed species that have the most of certain chemical compounds. When monarch larvae eat milkweed with these compounds, they become poisonous to potential predators. Two milkweed plants the U.S. Forest Service says are favored by monarchs are Asclepias amplexicaulis in Eastern North America and Asclepias californica in Western North America.
Any flowering plant will attract monarchs. Some common flowers monarchs drink the nectar of are dogbane, red clover, thistle, lantana, lilac and goldenrod, according to the University of Washington NatureMapping Program. If you're planting an entire garden for monarch butterflies, provide a variety of flowers that bloom in different months. Include flowers that bloom in the fall, when monarchs need energy to migrate south. The University of Washington NatureMapping Program notes that in the fall, adults visit blazing stars, ironweed and tickseed sunflower. Like other large butterflies, monarchs prefer larger flowers with open, flat surfaces that they can stand on while drinking.
There are some general guidelines for drawing butterflies to gardens. The Missouri Botanical Garden Butterfly House recommends using colorful plants. Butterflies seem to be drawn to red, orange, yellow, purple and dark pink. A large, colorful garden is easy for butterflies to find, particularly as flowers wave in a breeze. Therefore, placing flowers that attract monarchs into groups in your garden, with three or more the same kind growing close together, will attract the most butterflies. It's also wise not to use chemical pesticides on the flowers. The Missouri Botanical Garden Butterfly House recommends using natural methods, such as planting marigolds, petunias, mint and other herbs that naturally repel pests, as well as using insecticidal soap. Also, encouraging beneficial insects, such as ladybugs, into your garden will help to keep pests under control. According to Pioneer Thinking, ladybugs are attracted to plant with umbrella shaped flowers such as fennel, dill, cilantro, caraway, angelica, tansy, wild carrot and yarrow. Other plants that also attract ladybugs, Pioneer Thinking notes, are cosmos (especially the white ones), coreopsis, and scented geraniums and dandelions.
Flowering plants aren't the only living thing you can grow to feed monarchs. Adult monarchs consume a variety of things, including liquids from fruits humans eat, according to the Monarch Butterfly Website. You can also plant fruit-bearing trees with blossoms that provide both nectar and, eventually, fruits that monarchs can also enjoy.