The answer is the Monarch butterfly requires milkweed for her babies.
The Monarch will lay her eggs only on milkweed and when the eggs hatch the larva will feed on the milkweed. Without the milkweed there would be no Monarch butterflies.
The second question you may ask is where can I get milkweed?
Most garden centers are currently selling a variety of milkweed called Tropical Milkweed. You may also find Tropical Milkweed called by other names such as Scarlet Milkweed or Butterfly Weed. Due to the different names used it can be confusing. In my experience, I have found that these are really Tropical Milkweed plants. Please note that the Tropical Milkweed plant is not a Texas Native plant. The Tropical Milkweed plant is a native Mexico plant.
Texas Native Milkweeds:
Nurseries do not appear to be selling native milkweed plants.
This is most likely due to the issue that Texas Native Milkweeds are harder to propagate and grow. This would most likely increase the cost of Texas Native Milkweed plants if you can find them. However, it is possible to start your own native milkweed by planting seeds.
Recommended Milkweed species for the Houston/Conroe area are:
Species Botanical Name
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Green milkweed Asclepias Viridis
Butterfly Weed Asclepias Tuberosa
Tropical Milkweed Asclepias Curassivica (note, this is not Texas native)
Sprouting of milkweed seeds can be tricky too. Cold scarification seems to be a must so you need to put seeds in refrigerator for several weeks to have proper germination.
Good web-sites to learn more about Texas Native milkweeds:
www.asclepias.org
Cautions:
When purchasing milkweed plants make sure the milkweed is not classified as ornamental. Ornamental will be a red flag that this milkweed has been sprayed with pesticides. If a garden center or grower has used systemic pesticides on plants it may take 6 months for the toxins to leave the plant. If you have any questions about the milkweed, be sure and ask the nursery or garden center.
Recommendations:
Start with Tropical Milkweed to learn the basics or if you only have a small area where you can plant milkweed. The Tropical Milkweed plant can be an attractive addition to your garden. Then later move on to more advanced activities like trying to grow your own Tropical or Texas Native plants from seed.
Having FUN:
After you have your plants you should soon be rewarded with Monarch females laying eggs on your plants. Provide the proper habitat and you should see Monarchs and other butterflies visiting your butterfly garden area. And the most important thing to remember is to have FUN!!!!.........