Invasive species management, tree and brush removal, and prescribed fire are three major components of our restoration work at the Arboretum, and so I’ve written a lot about them over the years. There’s also a fourth, however, which has gotten less attention even though it’s equally important, and that’s our seed collection and planting program.
In some parts of the Arboretum, the goal of restoration is to improve plant diversity. Historically, the original plant diversity was usually lost when land was plowed and converted to agriculture. Sometimes areas also became overgrown by trees and shrubs that shaded out the native prairie and savanna species. Even when the three main aspects of restoration efforts are applied, the native plants are not likely to recover on their own. So to aid their recovery, we add seed of the plant species we’d like to see growing.
Where do these seeds come from? When a restoration project is grant funded, we designate money to purchase seed from local native plant nurseries. But recently, more often than not, we have harvested seed from Arboretum plants throughout the year (our typical harvest season is May through November). Our existing restorations (such as Curtis Prairie and Greene Prairie) and remnants (West and East Knolls, and outlying properties) have an abundance of plant species we can harvest from.
Our seed collection methods are pretty basic. Sometimes we simply pluck the seed off the plant by hand; other times we use hand pruners to cut off the top of the plant holding the seeds. The plant material then all goes into a bucket. Pretty straightforward!
Drying the seed is the next step. We spread the collected material in thin layers on big trays to air out. We label everything with note cards that record species name, the unit where it was collected, and the date. (This information helps us know where and when to look for that species when harvesting in later years). Fans and dehumidifiers help with the drying. Sometimes, if the seed and plant material is extra damp, we turn it over several times a day. The drying is necessary to prevent mold, which can ruin the seed. Drying can also help the seed to finish ripening.
During the summer and fall months, we are busy harvesting, drying, and labeling. Dried seed gets stored in paper bags so they can continue to “breathe” and stay dry. Later in the fall, as the harvest season winds down, we begin to clean seed and prepare for making seed mixes. Cleaning involves trying to separate the seed from the rest of the plant material, which helps the seed make good contact with the soil when we plant it later. For some species, cleaning can be accomplished by simply running the material through a screen with your hands. For other species, we’ll process everything through a hammer mill. The little hammers in the mill spin really fast and knock the seed loose from the rest of the plant. It also grinds up the remaining plant material into chaff. The loose seed and the chaff end up in the same barrel after milling, but we do not spend much time separating them. The chaff helps us get good coverage when spreading seed.
After the seed is cleaned, we weigh it out by species. This helps us determine the total quantities of each, which then informs how we design our seed mixes. Some species only go into one mix (many of the wetland plants, for example, only go into the wetland mix). Others get divided and a certain percentage is placed into different mixes. Each mix is tailored to the specific area where we intend to plant it, to ensure that the species most likely to succeed are planted in appropriate areas. Having a record of the species and the amount planted in given areas will help us monitor them in the future to see how well the restorations are doing. We also add dried wood chips to our mixes. Similar to the chaff, it helps us get good coverage when we spread the seed. This year, we made mixes for various areas and habitat types, including: Lake Wingra shoreline, Southwest Grady Savanna, Grady Knolls Forest, general oak openings, general woodlands, and general wetlands, among others.
There are also species that we don’t include in mixes because we want to be particular about where they are planted. For example, this year we collected a lot of swamp loosestrife – a fairly unique wetland plant. We hope to get it established in places where it might compete with reed canary grass and improve low-diversity areas. Porcupine grass and some less common milkweeds are other species we plant individually.
Once the mixes are made, we wait for the right planting conditions. We spread seed by hand, and we like to plant in the late fall and early winter. Overwintering naturally provides the cold and wet conditions that some seeds need to germinate in the spring. We also like to take advantage of the freezing and thawing cycles of winter and spring that help the seed work into the ground. And ideally, we like to time our planting before the onset of a good snow. A couple inches of snow will help protect seed from seed predators such as turkeys and mice.
Over the last five years, as we’ve expanded our restoration work into new areas, we’ve made a concerted effort to expand seed collection as well. It’s gratifying to see these figures tracking the progress. As a crew, we’ve devoted more time to seed collecting. We’ve learned more about when certain species flower and produce seed and where those species are located, both of which help us increase our harvest.
The extensive burning we did in spring 2021 led to a major increase in flowering and seed production during the growing season, which helped us reach the big increase in quantity (some of that weight does include chaff). And we’ve learned more about the less common Arboretum species, which has helped us increase the number of species we’re harvesting.
As we continue to learn and improve our seed harvesting operation over time, the quality of our restorations should improve as well.
—Michael Hansen, land care manager