Our Nursery

When nurseries propagate plants through cuttings, cloning, or using seed collected from a small or cultivated population, they winnow out genetic diversity, rendering all the individual plants in the group susceptible to the same pests and diseases. That means that all plants of the same species that live in a particular geographic area can be wiped out by a single pest, as happened, for example, when one microorganism decimated Ireland's potato crop in the mid-19th century, causing a famine that claimed about a million lives.

In some cases we need to propagate plants through cuttings or another vegetative method, usually when a species is difficult to grow from seed or does not produce much, if any, viable seed. Also, native plant cultivars—varieties that have been bred for certain characteristics, such as resistance to disease, size, and ornamental traits—have their place in our landscapes, in moderation.

Take, for example, double blood-root (Sanguinaria canadensis ‘Multiplex’). A natural mutation in the wild created a plant with additional flower petals. Unlike the straight species, double blood-root is sterile—that is, it does not produce seed—because the mutation transformed its reproductive parts into petals. While we continue to collect wild seed of blood-root and grow it from seed, that is not an option for double blood-root and similar sterile plants. So, we may divide the plants, take cuttings, or purchase them from our partner nurseries that have propagated them from cuttings.

But these are exceptions. We primarily focus on growing native plants from seed collected in the wild by a team of trained staff and volunteers who research and document local sources of healthy, wild populations. At the right time, we head into the field to collect seed, careful to leave plenty of intact specimens to enable the population to continue to thrive. This widespread sampling in the wild ensures that the native plants we grow in our greenhouses represent the region's robust genetic diversity.

The study also documents the role that garden centers, many of which still sell invasive plants, currently play in seeding future invasions. Together, the papers, published in Diversity and Distributions and BioScience, and the publicly available maps, which track species at the county level, promise to give invasive species managers in the U.S. the tools they need to proactively coordinate their management efforts and adapt now for tomorrow’s warmer climate.

Seed propagation protocol for Carex pensylvanica at Nasami Farm

Author: Alexis C. Doshas; contributors: Cayte McDonough, K. Miho Connolly
Co-investigators: Alexis Doshas, propagator; Cayte McDonough, nursery manager; K. Miho Connolly, propagation assistant.

The following summarizes an article published in Native Plants Journal vol. 22 no. 1 (Spring 2021): 45-50. © 2021 by the Board of Regents of the University of Wisconsin System. Reprinted courtesy of the University of Wisconsin Press.

Pennsylvania sedge (Carex pensylvanica) is a desirable lawn alternative due to its turf-like appearance and habit, as well as its ability to thrive in dry soils and partial shade. It is a clumping sedge growing 8 to 12 inches tall with fine, pale-green leaves. It spreads by rhizome to create turf-like ground cover in forests, savannas, and dry light shade. It is also notably difficult to propagate from seed. Its low germination rate (at Nasami Farm, about 10% germination annually) limits the use of this species in large-scale restoration projects and makes it challenging to find genetically diverse, seed-grown stock in the horticultural trade. Genetic diversity is important for creating resilient landscapes able to withstand disease and climate fluctuation, and to support diverse ecosystems. The majority of propagation of C. pensylvanica is achieved through division or tissue culture, both of which result in a clonal specimen and contribute to a monoculture in the designed and restored landscape.

As protocols for seed propagation in a nursery did not exist, our objective was to improve germination of C. pensylvanica and develop a seed-propagation protocol. Beginning in 2017, Nasami Farm nursery staff members conducted a series of multi-year trials to determine best practices for nursery production of seed-grown C. pensylvanica. We began by looking at the effectiveness of three treatments on germination of C. pensylvanica seed: perigynium manipulation, variation in sowing depth, and warm stratification.

The achenes of Carex spp. are enclosed in a papery, bladder-like sac called the perigynium (plural, perigynia), which tightly adheres to the pericarp. In some Carex species this causes a physical barrier to germination. We tried full removal of the perigynium, partial abrasion of the perigynium, and leaving the perigynium intact.

Another factor that can affect germination is sowing depth. We tried sowing seeds on the surface of the soil, and with light cover. Finally, we looked at a warm dry stratification, or "after-ripening," in which the seeds are stored in a warm, dry location (~70 degrees) for a 12-week period. This mimics the ecology of the seed, which ripens in May and June, disperses, and undergoes the warm summer season before entering into a cold stratification of winter.

In our first set of trials we found the highest germination rates (68-72%) in seeds that underwent a 12-week warm stratification period prior to being sown. Further, among the warm-stratified seeds, seeds that were sown with a light cover of growing medium had better germination rates than seeds sown on the soil surface. Perigynium manipulation did not result in improved germination. A second-year study confirmed these results. In year three we ran trials to determine the minimum required period of warm stratification to produce successful germination. We found no reduction in germination in our 9-12 week warm-stratification trials, allowing us to refine our protocol and required time. With a reliable germination rate, we could then explore streamlining our production by direct seeding into plug trays, eliminating the step of transplanting seedlings.

Since 2021 we have been able to increase our production of seed grown C. pensylvanica plugs from 10% grown from seed to 100% grown from seed, and to do so efficiently and sustainably. (Prior to instituting this new propagation protocol, we propagated C. pensylvanica from divisions of seed-grown plugs.) We now produce six times more C. pensylvanica plants, or 3,800 plugs annually, than before introducing the warm- and cold-stratification. By refining and sharing germination protocols, we hope to contribute to a greater supply of genetically diverse plant material in the trade and in our landscapes.