Milkweed (Asclepias spp.) is the host plant for caterpillars of the monarch butterfly. Not only is milkweed a great nectar source for hungry butterflies and other pollinators but it is required for the survival of monarchs. Monarchs are in decline due to habitat loss. Look at undeveloped fields in our area in the spring and you will find (native) milkweed growing and thriving naturally. To help the monarchs, many homeowners are now growing milkweed in backyard gardens.
Why all the controversy surrounding tropical vs native milkweed?
Tropical milkweed (Asclepias curassavica) has year-round foliage and flower production in southern states. This allows for monarchs to continue breeding and laying eggs instead of migrating further south to overwinter in Mexico. Those that stay do not survive our freezing temperatures in winter. Tropical milkweed has also been studied for its role in the spread of OE (Ophryocystis elektroscirrha), a parasite that infects butterflies that host on milkweed, including the monarch. OE in monarchs increase where tropical milkweed flourishes. If an infected milkweed continues to thrive through winter and does not die back like native milkweed species, the infected plants will persist and continue to infect monarchs the next season and throughout spring and fall migrations.
What do you do if you already have tropical milkweed?
Sometimes tropical milkweed is all we can find in our local big box stores. If you grow tropical milkweed, be diligent about cutting it back in early October and keeping it cut to 6 inches throughout fall and winter. This will discourage monarchs from creating a breeding ground and will help to eliminate OE spores present on the plant. Try to find a retailer that sells native milkweed plants or seed. Some local nurseries sell native milkweed in the spring but be sure to ask about pesticide use…a nursery milkweed plant that has been treated with pesticide will kill the larval (caterpillar) stage of a monarch.
What native milkweed should you look for?
Texas has over 30 native species of milkweed. With several that grow easily in North Texas. The two most common native milkweed species that grow in North Texas are Green Milkweed (Asclepias viridis) and Antelope Horn Milkweed (Asclepias asperula). Another native species, Butterfly Weed (Asclepias tuberosa), is a showier option with beautiful orange flowers, not to be mistaken for tropical milkweed! Keep in mind that flowers do not usually appear until the plant is well-established. However, monarch butterflies will still utilize the plant to lay eggs and the caterpillars will complete their lifecycle happily feeding off the leaves.
Antelope Horn (Asclepias asperula)
Green Milkweed (Asclepias viridis)
Butterfly Weed (Asclepias tuberosa)