Two Identical Plants: One Saves Butterflies, The Other Kills Them

We’ve been taught that milkweed is the favorite food of monarch butterfly caterpillars. So, gardeners should plant milkweed to save the butterflies, right?


Not all types of milkweed are beneficial to monarch butterflies. In fact, gardeners that plant the wrong type of milkweed may be killing butterflies.

Butterfly weed vs tropical milkweed

Milkweed is Important for Monarch Butterflies

Milkweed is the only plant Monarch butterflies will lay their eggs on. The caterpillars that hatch from the eggs eat only milkweed leaves. In addition, adult butterflies feed on the nectar in milkweed flowers to survive.

  • Monarch butterflies lay their eggs on milkweed plants ONLY.
  • Milkweed is the diet of monarch butterfly caterpillars.
  • Adult monarch butterflies eat milkweed nectar.
  • Eating milkweed gives monarch caterpillars and butterflies a natural defense against predators.

Milkweed sap contains toxins. By eating milkweed leaves the caterpillars collect these toxins in their body. Any bird or other animal that tries to eat a monarch caterpillar or adult butterfly will then be poisoned. This teaches animals to avoid eating monarch butterflies, which allows these butterflies to survive in the wild.

Monarchs May Disappear Without Milkweed

Monarch butterflies disappear from regions where there is little or no milkweed. This has led to dangerous declines in monarch butterfly populations in the United States. The butterflies gather near milkweed to meet mating partners, feed, and lay eggs. Without milkweed, monarchs cannot continue their life cycle, so the adults die without laying eggs.

  • Monarch butterflies won’t gather to mate and lay eggs if there is no milkweed nearby.
  • Regions without milkweed don’t have the proper food for monarch caterpillars.
  • Monarch caterpillars fed a non-milkweed diet are more likely to be eaten by predators.

In some cases, people have reported monarch butterflies laying eggs on squash plants. However, this has not been reliably documented. Even if monarch caterpillars can survive on other plants, they won’t develop the natural toxic defense they get from milkweed sap. This makes young monarch caterpillars far more vulnerable to being eaten.

Tropical Milkweed is Deadly to Monarchs

Tropical milkweed (Asclepias curassavica) is deadly to monarch butterflies because it stops them from migrating away from cold winters. Let me explain.

Monarch butterflies migrate from the United States to Mexico each winter. The butterflies know they have flown far enough south when they find tropical milkweed, which is native to southern Mexico. Once they find this plant, the monarchs stop traveling south and settle in for the winter.

  • Tropical milkweed is native to areas with very warm winters—not the United States.
  • When monarch butterflies find tropical milkweed, they stop migrating south.
  • Monarchs that find tropical milkweed in the United States stop migrating south. Then, they die during winter.

The problem is that many gardeners in the United States have begun growing tropical milkweed in their flower beds. When monarchs find these plants, they stop migrating south for the year. Then, because the winters in the United States are colder than southern Mexico, the monarch butterflies are killed by the cold weather.

This is why it’s essential to NEVER plant tropical milkweed in the United States. Growing this plant will bring butterflies to your yard, but it will also kill them. Instead, only grow milkweed species that are native to the United States. This way, the butterflies will continue migrating south and survive the winter.

Below, we’ll cover the best milkweed varieties to grow in your garden.

Adding the Right Milkweed to Your Garden is a Great Idea

It is a great idea to grow a local milkweed species in your garden. Growing native milkweed will provide a place for monarch caterpillars to turn into butterflies. Plus, there are a ton of other benefits to milkweed, such as keeping away ticks and pest insects.

  • Growing a native, local milkweed species is an excellent way to save butterflies.
  • Milkweed is a fantastic garden plant with beautiful flowers.
  • Avoid planting exotic milkweed varieties—they can harm butterflies.

The important thing is to avoid growing non-native milkweed species in your garden. There are 140 milkweed species found around the world, but some common ornamental species are not safe for butterflies.

Several Great Milkweeds for Butterflies

Butterfly milkweed (Asclepias tuberosa) is the best choice for growing milkweed in your garden. It has bright orange flowers and provides the perfect food for monarch caterpillars. The National Wildlife Federation also states that swamp milkweed and common milkweed are good choices for gardeners.

  • Butterfly milkweed, common milkweed, and swamp milkweed are the best choices for US gardeners.
  • Avoid planting species of milkweed that are not native to your area.
  • Contact a native plant nursery for information on the best milkweed species for your garden.

It’s always a good idea to feed wildlife with plants that are native to your region. If you’re unsure what species of milkweed grows naturally nearby, speak to an expert at a nearby native plant nursery. They can point you in the right direction and may have native, flowering milkweed for sale.

Don’t Plant Harmful Milkweed

Never plant tropical milkweed in your garden. In addition to preventing natural migration, researchers have also found that tropical milkweed hosts parasites that are deadly to monarch butterflies. This makes tropical milkweed one of the worst plants you can grow.

All non-native types of milkweed pose a threat to the environment. Since milkweed can spread quickly and invade local ecosystems, it’s best to only plant native varieties. Growing native plants will help local wildlife and prevent several species from going extinct.

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