In large or small scale ecological restoration projects, it is important to use native seeds or plants that originated within the same region where they are being planted. Plant species can develop different traits in different geographic regions that make them more suitable for that particular region. For this reason, using locally sourced seeds in restoration projects can help to promote a higher degree of success in the plants being established in the area and can minimize genetic “pollution” by plants sourced from outside the region.
The Monarch Joint Venture is working closely with the Iowa Department of Natural Resources Prairie Resource Center to restore milkweed and nectar plant habitat in prairies throughout Iowa, but also to create a supply of local, native milkweed seeds for use in future restoration projects. In 2013, the Prairie Resource Center planted 2,621 acres to native grasses and forbs, including four different species of milkweed and two important nectar sources (Liatris pycnostachya and Liatris ligulistylis). They also partnered with the Tallgrass Prairie Center at the University of Northern Iowa to establish milkweed seed plots for Asclepias tuberosa and A. sullivantii. Seed from these plots will be utilized to enhance Prairie Resource Center and Tallgrass Prairie Center restoration projects, and will also be used by private seed producers to start local ecotype plots for the species, which will in time provide seed for other restoration efforts. This year’s harvest of the Tallgrass Prairie Center’s A. tuberosa plots yielded 8.29 bulk pounds of seed in September, which were harvested both by hand and mechanically.
The next sections will describe different tips and methods for collecting milkweed seeds. Thank you to Brianna Borders of the Xerces Society for providing this information on harvesting milkweed seed. Xerces has also collaborated with milkweed growers like the Iowa DNR and Tallgrass Prairie Center to help inform a new document that they will release in winter or spring 2014, Milkweeds: A Conservation Practitioner’s Guide. It is a comprehensive publication that includes information on milkweed ecology, the plants’ value to monarchs, pollinators, and other beneficial insects, and detailed guidelines for milkweed seed production. Once finalized, this document will be freely available for download from the Xerces website.
Milkweed pods within a given population or production stand ripen over a period of a few to several weeks and a subset of them will likely be ready for collection each day during that time. Due to the wind-aided dispersal of milkweed seeds, the window of opportunity for harvesting mature seed from any individual pod can be narrow. There are several strategies for milkweed seed collection, depending on the scale of the collection effort and the equipment and labor force available. Here we highlight approaches to both small-scale hand harvesting and large-scale mechanized harvesting.
When collecting between several grams to a few ounces of seed (e.g., one to several handfuls) from a wild population, garden-grown plants, or a small seed production plot, hand harvesting is a straightforward method that doesn’t require any specialized equipment. If it is challenging to visit the plants on a regular basis within the seed collection window, there are a few tricks you can use to increase your chances of making a successful collection. Seed capture bags, made from a variety of materials, can be affixed over maturing pods and retrieved at a later date. Using these bags can give a seed collector several days of flexibility in scheduling a return visit. Also, rubber bands or cable ties can be applied to the widest part of nearly mature pods, to prevent them from fully dehiscing. As compared to seed capture bags, rubber bands and zip ties are lower cost and less conspicuous, but their use may only extend the collection window by a couple of days. The seeds are likely to fall out of the pod if one does not return to collect them soon after the pod splits. One notable drawback to using seed capture bags is that leaving the bags in place until after the pods have fully opened will increase the amount of time and labor required to later separate the seeds from floss (as compared to strategically harvesting pods that have not yet dehisced). Before attempting to collect seed from wild populations, it is essential that you acquire the necessary permission for land access and seed collection activities.
Photos: (left) Rubber bands affixed to maturing pods of pinewoods milkweed (Asclepias humistrata) by Jeff Norcini, Oecohort, LLC. (right) Seed capture bag made from polypropylene garden fabric, on A. asperula, by Desert Botanical Garden
At the opposite end of the spectrum, as far as scale, is the challenge of harvesting seed from production stands that consist of several hundred or even thousands of plants. Some commercial milkweed seed producers report that hand-harvesting is an efficient approach for milkweed production stands less than an acre in size. However, a significant labor force can be required to complete the harvest over a period of several days, and some producers opt to utilize mechanized harvesting equipment, for efficiency. The milkweed seed crop is ideally harvested during the estimated peak of pod maturation. Some hand-harvesting can be done toward the beginning of the seed ripening period, to capture early-maturing pods. Combines in particular are very effective at breaking up harvested plant material and separating seeds from their attached floss fibers (which helps save significant time on post-harvest seed processing). The threshing action of the combine releases seeds from the pods and breaks down vegetative material, while most of the floss fibers exit the machine. Combines are so effective at removing milkweed floss that even if the equipment has not been used for harvesting, some seed producers feed large quantities of hand-collected pods into a stationary combine, to complete the initial phase of seed processing. Due to the variable growth form among milkweeds, some species may combine more readily than others.
Photos: (left) Hedgerow farms hand-harvesting narrowleaf milkweed (A. fascicularis) pods, by John Anderson, Hedgerow Farms. (right) Milkweed floss exiting a combine, by John Anderson, Hedgerow Farms.
You may not own a milkweed seed plot, or a combine for harvesting the seed, but there are plenty of ways for you to help spread locally sourced milkweed seeds to your community. First, using the tips outlined here, collect some, but not all of the seeds from your milkweed patch when they have ripened and share them with friends and neighbors, encouraging them to plant the seeds to help monarchs by creating habitat. Second, if you have an abundance of seeds, consider sharing some with a local native plant nursery for them to grow and distribute the following spring.