Ask Mr. Smarty Plants

Perhaps you have already read it but, if not, please read our How-To Article on Butterfly Gardening. We are going to our Native Plant Database, and search on "milkweed;" we will again search on the state of Texas and then check each milkweed on that list to see that it grows naturally in Travis County. From there, we will give you that list and examine the webpage on each species of milkweed to see if specific instructions on carrying the plant safely over the winter can be found. We found 49 plants with "milkweed" in their common names, 33 of those native to Texas and 5 listed in USDA Plants Profile as native to Travis County. That doesn't mean that only those 5 will grow in Travis County but only those 5 have been reported to the USDA as growing here. All are perennial and have basically the same growing conditions.

Members of the genus Asclepias (milkweed) native to Travis County, TX:

Asclepias asperula (Spider milkweed) (also called Antelope horns)

Asclepias texana (Texas milkweed)

Asclepias tuberosa (Butterflyweed)

Asclepias viridiflora (Green milkweed) (also called Antelope horns)

Asclepias viridis (Green antelopehorn)

Since you specifically mentioned the antelopehorn, we went to the webpage on Asclepias viridis (Green antelopehorn) and found these growing conditions, which should apply to just about any milkweed growing in this area:

"Growing Conditions

Water Use: Low
Light Requirement: Sun
Soil Moisture: Moist
Cold Tolerant: yes
Heat Tolerant: yes
Conditions Comments: This is another member of the milkweed family that certain butterflies love. It can be found growing in rich or poor soils and blooms off and on over ther growing season through the end of summer. Has a spreading, open growth form. Requires little water and full sun."

Asclepias asperula (Spider milkweed) is also referred to as Antelope Horns and it had this comment under growing conditions:

"Antelope-horns will inevitably have aphids. The insects are not a problem unless the plant looks sick; at that point an effective treatment is to spray the plant and aphids with soapy water. Another possible treatment is to support the plant part with your hand and blast it with high-pressure water."

"Asclepias tuberosa (Butterflyweed) had this additional comment:

Maintenance: Needs to be transplanted carefully and requires good drainage. It takes 2 – 3 years before A. tuberosa produces its vibrant flowers, which appear in 2 – 3 inch clusters of orangish-red. Once established, it lasts for years, becoming thicker each year."

The only real clue to your problem we found was the mention on the webpage on Asclepias tuberosa (Butterflyweed) that it needed good drainage. This is a common problem in the soils in Central Texas, which are often clay. Clay is composed of tiny particles which, when wet hold tightly together excluding oxygen. The tiny rootlets of plants need easier access to the soil they are in to get the water, oxygen and nutrients they need. The next time you add new plants, consider amending the soil with compost which could at least help.

After we had done all this research, we found a previous Mr. Smarty Plants answer that directly addressed your question.