The Monarch butterflies have a complex lifecycle and individuals are in the San Antonio area seeking out nectar sources for food and milkweed plants on which to lay their eggs.  I have seen them obtaining nectar from peach and plum blooms, blue curl, rain lilies, sweet peas, stock and Mexican honeysuckle. My tropical and native milkweed plants have been slow to recover from the November and March freezes but other gardeners report that their milkweed has produced enough foliage to host a hatch of Monarch caterpillars and is even starting to bloom.  That is good news because the migrants need to produce a new generation of butterflies before they die. That new generation will then head further north for several weeks before it lays its eggs and dies.  By the time the wave of migrating Monarchs reaches the Great Lakes and Southern Canada, it will have passed through 5 generations. That Great Lakes generation will then head south again, going through San Antonio again on its way to its wintering grounds in a small piece of forest in the highlands near Mexico City.

The fall of 2019 generation will visit us in September and October seeking access to enough milkweed, mistflower, zinnia, lantana, duranta, and other nectar to bulk up and make it to the wintering grounds before the cold weather arrives.

Just based on this abbreviated account of the Monarch life cycle, it is easy to identify some real points of vulnerability in the cycle.  Monarchs are vulnerable to severe weather events as they fly the several thousand miles from their northern breeding sites to their Mexican wintering grounds.  They require milkweed to support caterpillar production. Milkweed has been targeted as a dreadful weed in farming operations and eliminated on many sites.  The wintering ground in Mexico is only about 15 acres of land that has been vulnerable to illegal forest harvest. The net result was a severe reduction in Monarch populations in the last decade.

The good news is that the population that reached the wintering ground in 2019 was 144% greater than the population the year before. More good news is that the threat to Monarchs is one of those important issues in which local gardeners can intervene directly and have a positive impact.

  • Plant milkweed in your landscape. Tropical milkweed is the most attractive and easiest to grow selection. Native milkweeds such as A. tuberosa (butterfly weed), A. viridis (green milkweed), and A. asperula (antelope horn milkweed) have been harder for nurseries to produce, but they are now becoming available. Use tropical milkweed until you can grow enough native milkweed.
  • Have excellent nectar sources available in March/April and September/October when the migrating Monarchs move through San Antonio. Among the best are milkweed, mistflower, blue curl, zinnia, lantana, porter weed, duranta, cosmos, coneflower, Mexican flame vine, and fall aster.
  • Reduce your insecticide spray program to the minimum possible and avoid general sprays in favor of sprays such as Bt targeted to address a specific insect such as cabbage loopers on broccoli. It is unnecessary to control the aphids on milkweed and most other pests on flowers.
  • Joining one of the many habitat, education, or research initiatives may not be as direct an intervention as changing your plant selection and gardening practices in your backyard, but it is also important and effective. Review the “Monarch Initiatives” described on the internet and see if any meet your idea of the action needed.  Support and join those that attract your interests.
Written by Calvin Finch
Dr. Calvin Finch is the retired Urban Water Program Director for the Texas A&M Institute of Renewable Natural Resources.You can ask Calvin question and hear his answers on the air as he co-hosts the Gardening South Texas on the air at KLUP (AM 930) Saturday and Sunday from 12:00 to 2:00pm.