Updated: Jul 27, 2022
When my family bought this property almost 3 years ago now, I was excited to design a foodscape in the front yard. It was a clean slate to create something great. I really wanted this area of the front to pop with pollinator attracting flowers. I had learned in the past how critical pollinators are in the foodscape. What better place to have pretty colorful flowers than in the place they will be most visible and appreciated?
Milkweed was high up on the list of plants I wanted to landscape with. Supporting monarchs was another goal. The debate of native vs tropical milkweed didn't make a whole lot of sense to me at the time. To make matters worse, finding native milkweed was very difficult. Any milkweed would be better than no milkweed right? As long as something is feeding butterflies and hosting caterpillars I would be contributing to butterfly species right? And they in turn would bring entertainment and pollination to the foodscape?
So I planted around 20 tropical milkweed plants as a border in the front yard.
I have learned that I was wrong on those first two thoughts. Tropical milkweed did bring monarch and queen butterflies to the foodscape which was so much fun to watch. But the more I've learned about butterflies and milkweeds the more I realized it was a big mistake to ignorantly plant tropical milkweed. "... and good intentions may do just as much harm as malevolence, if they lack the understanding" - Albert Camus.
So today, after 2 years, I finally ripped them all out.
The main driving force behind ripping these plants out was the confirmation that tropical milkweed is a nonnative invasive milkweed that is actually hurting monarchs and the ecosystem itself. Here are a few reasons why.
Tropical milkweed is a native of Mexico. It does not go dormant in the colder months like the FL native milkweeds do. This interrupts the natural migration of monarchs south during the winter. As their food sources go dormant with lowering temperatures from north to south, it drives the monarchs south in search of food. If monarchs do not migrate far enough south when cold temperatures hit, they can die since they have no protection from the cold.
Since tropical milkweed does not go dormant, it can also increase the chance that it will become contaminated with OE - Ophryocystis elektroscirrha. OE is a parasite that infects monarchs. It is spread by spores carried on the outside of infected butterflies. As they go from milkweed plant to milkweed plant, the spores fall on stems and leaves. When caterpillars inadvertently eat the spores while consuming leaves, they become infected. The parasite rapidly reproduces and eventually kill the caterpillar. Typically, the caterpillar dies before it can emerge in the cocoon. Lesser infected monarchs may emerge but will not have the strength to fly very far. They most likely will be killed by predators, or will not be able to migrate far enough south in the winter.
Since tropical milkweed does not go dormant, OE spores continue to multiply on the plant. Native milkweeds reduces the risk of OE spread by going dormant in the winter. Since the plant dies back, any spores on the foliage will be removed. In the spring when new foliage sprouts, there will be little if any OE until is is spread through an infected butterfly.
Research has shown that tropical milkweed may has some effect on allowing OE infected monarchs to live longer. At first thought this sounds like a positive effect. But, by allowing infected monarchs to live longer, it also increases the spread of OE spores.
With the understanding of all this information so far, let's add in that monarchs are more attracted to tropical milkweed than native varieties. Scientists believe that the attraction is due to tropical milkweed containing higher levels of cardenolides - the substance in milkweed making it toxic. Monarch caterpillars are able to ingest milkweed leaves and allow the cardenolides to build up in their bodies. This is a method of defense against predators. The toxin in their bodies makes them bitter tasting to a would-be predator warning them to the toxicity.
When grown together, female monarchs were observed laying eggs on tropical milkweed instead of native milkweeds. Somehow, the female monarchs can sense that tropical milkweed have more cardenolides. So, she thinks that using it as a host will better protect her future young. She is right. Kinda. In a perfect world more cardenolides will help protect caterpillars. However, more research is showing that in warmer climates and warmer times of the year, the amount of cardenolides in tropical milkweed is actually above the caterpillar's threshold. So tropical milkweed may actually be poisoning caterpillars to the point of death.
As if that weren't enough, tropical milkweed can easily spread and is invasive. Its seeds can be carried in the wind far distances. Cuttings from pruning root very easily. Just in my own yard, I have found tropical milkweed sprouting from seeds 10 yards from the nearest established plant. I have also found tropical milkweed growing in undisturbed wood lines around residential areas. So if tropical milkweed begins spreading into our undeveloped land who is there to manage it?
In the past few years, the compromise between the native advocates and the tropical milkweed advocates has been this:
IF, you are going to grow tropical milkweed... It needs to be solely for support of monarch and queen butterflies. It should never be allowed to go to seed. It MUST be pruned down to the ground in the fall to replicate a dormancy similar to native milkweeds.
And that is what I did with tropical milkweed in my yard. I pruned seed pods. The week of Thanksgiving I pruned it down to the ground. But the more I read and grow as a gardener, the more I believe that tropical milkweed doesn't have a place in the garden. Seeing new plants sprout away from the established plants was a glimpse into how I was contributing to the spread of an invasive plant. So I tore out all my tropical milkweed. It gone. Sayonara.
What are native milkweeds and where can you get them? In Florida we have many native milkweeds but there are only 3 that I have been able to consistently find in nurseries. They are:
Asclepias tuberosa - Butterfly milkweed
Asclepias incarnata - Swamp milkweed
Asclepias perennis - Aquatic milkweed (also can be called White Swamp Milkweed)
Native nurseries throughout the states should carry these during the growing season. I have personally found them at:
Green Isle Gardens - Groveland, FL
Lukas Nursery - Oviedo, FL
Rockledge Gardens - Rockledge, FL
Debary Nursery - Debary, FL
Or Check out our online store to see if we have any in stock.
I hope that this post gave you some good information on the impacts of tropical milkweed that you may have never known before. I encourage you to read more about monarch butterflies, OE, and milkweeds. There is so much information out there to help guide us in really contributing to the ecosystem and not hurting it more. Here are some website that I used to help make sure I was giving accurate information.