Testing how well native milkweed grows
Earlier this spring, a group of 100 gardening volunteers and organizations joined me in a series of classes at Milberger’s, the Dreamhill Estates Education Resource Center and the New Braunfels headquarters of the Comal County Master Gardeners to take inventory and improve our knowledge of growing milkweed. The goal has been to help meet the needs of migrating monarch butterflies for sites to lay their eggs and raise new generations of caterpillars.
Monarchs will only lay their eggs on milkweed, which is a target of agricultural weed control. During the annual monarch migration, four generations of adults are replaced and the butterflies survive the trip from Central Mexico to Canada and back. The result in recent years has been a reduction in population by 70%.
The reduction in the monarch population is caused by a combination of factors, but the one that seems to most attract the interest of local gardeners is the need for more milkweed as caterpillar-raising sites. It is the part of the problem that appears most possible for volunteer gardeners to address.
At first, it may appear to be simple to solve. There are a relatively large number of native milkweed species across North America, including at least seven in the San Antonio area. Green milkweed, antelope horn milkweed, butterfly weed, swamp milkweed, showy milkweed, common milkweed and zizodes milkweed are on our list.
Milkweeds are generally drought-tolerant but include species that tolerate poorly drained and almost all other types of soil. They generally have deep roots and are very difficult for farmers to control.
It turns out that despite the large number of species and their diversity, native milkweeds are hard to grow. Most seem to require cold to germinate and three to four years to mature, according to data provided by
the Native American Seed Co. in Junction.
The zizodes milkweed, a species identified by another of our cooperators, Douglas King Seed Co., seemed easier to germinate, and we gave it attention in the classes.
Zizodes milkweed germinated at a 70% rate without a cold treatment. We have been able to transplant the seedlings from the 3-inch container in which they were seeded into raised bed gardens.
The most noticeable characteristic of the seedlings was the production of a large root mass in the container that made them easy to transplant. The top of the plant varied from 1 to 4 inches tall after six months of growth in full sun with daily watering.
The first plantings of antelope horn, green milkweed and butterfly weed were placed in the same 3-inch containers as the zizodes milkweed. After three months with no germination, they were moved into the refrigerator for one month, and then into the same full sun site as the zizodes milkweed.
Sixty percent of the butterfly weed germinated and was transplanted into the raised bed. All the butterfly weed grew 1 to 3 inches tall during the period. None of the antelope horn and green milkweed in this sample germinated.
An additional planting included antelope horn, green, showy and swamp milkweed. After planting in the 3-inch container, they were immediately
placed in refrigeration for 45 days, and then relocated to the site described for the other plantings. After two weeks, there still is no germination.
Our plan now is to schedule more classes to present these results. In addition to the results from our planting exercises, we will attempt to recruit other gardeners who have experience growing local milkweeds and provide the seed to utilize the best techniques discovered.
The goal will be to arm gardeners with successful techniques for growing the native species and, as a result, expand the number of plants available for monarch egg-laying.
If you have experienced such success, please contact me.