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Master Gardener: Why milkweed plants are so important for monarchs
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Master Gardener: Why milkweed plants are so important for monarchs

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I’ve seen posts on social media about how important it is for us to plant milkweed for the monarch butterflies. What is the big deal? BF

I am glad you are seeing these posts, that means word is getting out and more people are realizing the importance of milkweed in our gardens. Here’s the deal.

For the most part, there are two monarch populations in the United States. There are the eastern monarchs and the western monarchs. The Rocky Mountains serve as the dividing line between the two.

Western monarchs can spend their summers in northern California, Oregon, Washington, and even the Vancouver, Canada area. Then as winter approaches, they migrate back down to Southern California, primarily in coastal areas.

Eastern monarchs are the ones we see in Tulsa. These butterflies pass through our area in the spring on their way north and then again in the fall as they head south to their overwintering site in Mexico. Monarch butterflies are one of the few insects that migrate such great distances.

The interesting thing about the monarch migration is that the monarchs that leave Mexico headed north are not the same ones that return in the fall. It is a multigenerational migration pattern that begs many questions like: How do they know where they are going? It is a fascinating story you can read about on the internet.

The problem we are facing with the monarchs is that their populations are in severe decline. In the ‘80s, the western monarch population was estimated to be about 4.5 million. By around 2015, that number had dropped to about 30,000, and in 2020, only 2,000 western monarch were counted.

The eastern monarch butterfly population gets counted a little differently. The over-wintering site in Mexico counts how many acres (or hectares) are occupied by monarchs, as you can imagine the difficulty in counting millions of moving butterflies. But the downward trend is similar. During the 2018-2019 season, it was determined there were 15 acres of overwintering monarch. This number fell to 7 acres for the 2019-2020 season, more than a 50% decline.

There are a variety of factors that influence these numbers, but one of the primary factors is a decline of available natural habitat along their migration paths due to agriculture and urban development. Pesticides are also a problem. The bottom line is that the primary food source for monarch caterpillars is disappearing.

Imagine you could only eat one food and that food was getting harder and harder to find. Kind of like the toilet paper crisis of 2020 but with much more dire consequences. Essentially, if you couldn’t find food, you would cease to exist. That explains the current situation with one of our favorite butterflies, the monarch.

While monarch butterflies are fueled by nectar from a variety of flowers, their caterpillars have one food: milkweed. Female monarchs search for milkweed on which to deposit their eggs. Once these eggs hatch, these baby caterpillars begin to eat, and boy do they eat. They can eat an entire milkweed leaf in about a minute and they continue to do so, gaining about 2700% above their original weight. To put this in perspective, that would be like a 6-pound infant eating enough to grow to be more than 16,000 pounds. So yes, they eat.

Milkweed also helps monarchs survive in that milkweed contains glycoside toxins. While this is toxic to animals (please wear gloves when handling milkweed), it works for the monarchs in that would-be predators know not to bother them due to the toxin. There is actually a very famous photo series that shows a blue jay eating a monarch and then spitting it out. That’s good enough for me.

If you have pets, you may want to hit the pause button on milkweed because it can be toxic to dogs, cats and horses. And if you are going to handle it, be sure to wear gloves and don’t touch your eyes. We don’t have any outside pets at our house so I am comfortable having milkweed in our garden, but you will have to make that decision for yourself.

There are a variety of milkweed plants that do well in our area, but they can sometimes be difficult to find for purchase. Fortunately, we have a good selection in our Online Plant Sale Fundraiser this year (tulsamastergardeners.org). Quantities are limited, so if you have an interest, now is the time to shop. We also have a large selection of flowers that will attract pollinators in general, so you can turn your flower garden into a pollinator habitat. If you really want to dive in, you can become a certified monarch waystation. To do this, visit monarchwatch.org.

All of this is to say that one of the best things we can do for the monarchs who visit us a couple of times a year is to add milkweed to our gardens.


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You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th St., or by emailing us at mg@tulsamastergardeners.org.

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