Milkweed serves a singular ecological function as the only host plant for the Monarch butterfly caterpillar. The Monarch population relies entirely on this plant genus, Asclepias, for survival during its larval stage. Texas is a geographically central corridor in the annual North American Monarch migration route. The state sees two significant waves of butterflies, first in the spring moving north and again in the fall traveling south to overwinter in Mexico. Planting milkweed in Texas gardens directly supports this natural phenomenon by providing the necessary food source for migratory generations.
Selecting Native Milkweed for Texas
The choice of milkweed species is important for supporting Monarch health within the Texas environment. Native milkweeds are adapted to the local climate, entering a natural dormancy period in the winter months. Species such as Butterfly Weed (Asclepias tuberosa), Green Milkweed (Asclepias viridis), and Swamp Milkweed (Asclepias incarnata) are excellent regional choices that naturally die back. This die-back aligns with the Monarch’s migratory cycle and prevents disease buildup.
A major concern in milder Texas climates is the widespread use of non-native Tropical Milkweed (Asclepias curassavica). Unlike native varieties, this species often does not die back when temperatures remain above freezing, allowing it to persist year-round. This continuous growth enables Monarchs to breed outside of their natural migratory timeline.
The year-round availability of Tropical Milkweed can lead to the accumulation of spores from the protozoan parasite Ophryocystis elektroscirrha (OE). When infected adult Monarchs lay eggs on these plants, the resulting caterpillars consume high concentrations of spores. This exposure increases the rate of OE infection, leading to deformities and a weakened migratory population. If Tropical Milkweed is present, it is recommended to cut it down to the ground every fall and winter to simulate natural dormancy and reduce the parasite load.
Optimal Planting Windows Across Texas
The optimal time to plant milkweed in Texas depends on whether you are using seeds or purchasing established transplants, and which geographic region you reside in. Seeds from native milkweed species require cold stratification—a period of cold, moist conditions—to break dormancy. This process can happen naturally outdoors during the winter or artificially in a refrigerator.
For planting seeds, a late fall or early winter window is preferable, allowing nature to perform the necessary cold stratification. Sowing seeds outdoors from late October through December ensures they are exposed to the required chilling period to germinate successfully in the spring. Transplants, which bypass stratification, should be placed in the ground after the average date of the last hard freeze.
North Texas and the Panhandle
The northern third of Texas, including the Dallas-Fort Worth area and the Panhandle, has the latest average last freeze dates. In the DFW metroplex, the last freeze is typically around mid-March, but in the colder Panhandle, this can be as late as mid-to-late April. Therefore, the safest time to plant milkweed transplants is from late March to early May, once the danger of frost has passed. Fall planting of seeds should occur between late October and mid-December to ensure the seeds experience a sufficient cold period. Early spring planting of transplants maximizes the time the plant has to establish its deep taproot before the summer heat.
Central Texas
Central Texas, encompassing the Austin and San Antonio regions, experiences a milder winter, which shifts the planting windows earlier. The average date for the last freeze often falls in late February or early March, sooner than in North Texas. This earlier warming allows for an extended spring planting season. Transplants can be placed in the ground beginning in mid-March and continuing through April. For native seed sowing, the late fall window remains consistent (late October through December), but the milder winter often means the seeds emerge earlier in the spring.
South Texas and the Gulf Coast
In the warmest parts of the state, including the Gulf Coast and the Rio Grande Valley, the risk of frost is minimal. This extended growing season allows for the earliest planting, often starting in February or even January in the farthest southern zones. The primary challenge here is the intense summer heat and humidity, which can stress young plants. Planting transplants early in the spring (late February to mid-April) allows the milkweed to establish a robust root system before the summer’s extreme temperatures arrive. For seeds, the natural cold stratification requirement may be inadequate, making artificial stratification in a refrigerator for 30 to 60 days a more reliable method before sowing in late winter.
Successful Planting and Establishment
The successful establishment of milkweed begins with correct site selection, which must prioritize full, direct sun exposure. Milkweed requires six or more hours of direct sunlight daily to thrive and produce the most foliage for Monarch caterpillars. The preferred soil should be well-drained, as most native milkweeds are intolerant of standing water or constantly saturated conditions.
When planting a nursery-grown transplant, it is important to “harden off” the plant if it was grown in a greenhouse, gradually exposing it to outdoor conditions over a week before planting. Milkweed develops a deep taproot, so transplants should be disturbed as little as possible when moving them into the ground. After planting, regular watering is necessary for the first few weeks until the plant becomes established, after which its drought tolerance will increase.