Ask Mr. Smarty Plants

There are no photos that I could find of Asclepias emoryi (Emory's milkweed) on the internet.  You can see a drawing of it in A Field Guide of Southwestern and Texas Wildflowers by Niehaus, Ripper and Savage on page 70.  You might be able to find this book in your local library.  The description of it reads: 

"Each cometlike white flower has a blunt "nose" and a trailing tail of greenish yellow, reflexed petals with thin white margins.  Slender, tawny yellow hoods with white enlarged tips project inward over the central column.  Lancelike leaves with wavy margins, fuzzy hairs, and petioles.  10-30 cm.  Plains.  Southern half of Tex.   MARCH-OCT."

The Mother Earth News' Sources for Monarch Butterfly Waystation Plants has a list of nurseries and seed companies all over the United States that specialize in milkweed plants.  You need to look at their web pages or telephone them to find out the availability of milkweeds.  Other possibilities for nurseries or seed companies with milkweed plants or seeds can be found by searching in our National Suppliers Directory.

Whether Asclepias texana (Texas milkweed) would do well with water only once a week would depend on the temperature and how much water it received the last time it rained or was watered.   It would do better in cooler winter weather than in the heat of summer.  You would need to monitor it and water it when it shows any tendency to wilt.  It should do fairly well in dry conditions once it is established (see "Growing Conditions" on its page—the link above—in our Native Plant Database).

Asclepias linearis (slim milkweed) grows in clay soils, roadsides and other disturbed places, Asclepias oenotheroides (zizotes milkweed) is widespread in open dry ground, Asclepias emoryi grows in disturbed places and roadsides and Asclepias curassavica in moist places according to Alfred Richardson in Plants of the Rio Grande Delta (pp. 199-200).

Check the resources page of Texas Monarch Watch for more information about milkweeds.

You might consider buying a copy of Milkweed Monarchs and More: A Field Guide to the Invertebrate Community in the Milkweed Patch by B. Rea, K. Oberhauser and M. Quinn to learn more about milkweeds, monarch butterflies, and other insects and related critters associated with milkweeds.