October is the heart of autumn as fall color develops and peaks in woodlands and prairies, on trees, shrubs and grasses. Our garden tasks include harvesting seed, removing or reducing aggressive native plants, trimming along paths, completing plant lists, and measuring areas to rework. We’re also entering garden data, writing summaries, and planning.

On dry sunny days in late summer and early fall, garden staff and volunteers harvest seeds from many native plant species. We generally harvest less than half of the seeds in an area, leaving some to germinate and some to be eaten by animals. In places where seeds fall on pavement or where we want to prevent a species from dispersing, we remove as many seeds as possible. Seeds collected in the native plant garden are used in the seed mixes the land care staff create for active restoration areas.

Collecting seed yields new plants in our gardens and restorations and is also an excellent way to understand the structure of fruits, the size and arrangement of seeds, and how they disperse. Seeds we’ve collected recently include white and purple prairie clover (Dalea candida and D. purpurea), leadplant (Amorpha canescens), thimbleweed (Anemone cylindrica), and Culver’s root (Veronicastrum virginicum). All these bear fruits (with seeds) along a stem where small individual flowers bloomed from base to tip of the inflorescence. We harvested seeds from species with single flowers, such as giant St. John’s-wort (Hypericum ascyron) or in heads or clusters, like rosinweed (Silphium integrifolium), meadow blazing star (Liatris ligulistylis), and sweet Indian plantain (Hasteola suaveolens). We notice the pleasant scent of yellow coneflower (Ratibida pinnata) and sweet black-eyed Susan (Rudbeckia subtomentosa) seed heads, and the unpleasant odor of mature capsules and seeds of smooth penstemon (Penstemon digitalis).

To expand your garden or start a new one, even one or two plants will yield many seeds. However, not all will germinate and grow immediately. The following examples have the same requirements for breaking seed dormancy (60 days of cold, moist treatment), but Silphium species seeds are relatively large (1,800 seeds/ounce) compared to St. John’s-wort seeds (225,000 seeds/ounce). Seeds of the latter are so small they should not be covered by soil when they’re planted. Information about the number of seeds per ounce is important for creating seed mixes and calculating how much seed is needed to cover a given area. You can look up seed per ounce values in native plant nursery catalogs and websites.

Some of the native plants we manage disperse into gardens or spread so effectively that they suppress other species and reduce diversity over time. Examples in the prairie garden include Canada goldenrod (Solidago canadensis) and woody shrubs like staghorn sumac (Rhus typhina) and gray dogwood (Cornus racemosa). Learning about the root systems and timing of growth of each species informs management methods to try.

Recently we decided to reduce the amount of sweet black-eyed Susan in the Friends’ terrace garden. It had seeded in from the rain garden nearby and grew exceptionally tall this year due to early season rains. We learned that each plant enlarges outward from an original plant via very short, shallow, thick rhizomes, with new buds emerging about an inch from the older plant. Over a few years, a cluster of stems is produced within a small area. We pulled many of the stems (eliminating the seeds they produced this year as well as the buds that would have emerged next year) and cut some off at ground level (eliminating the seeds only) to see if those are successful next season. This example illustrates how close observation and trials may lead to effective management methods. We may learn if dividing these plants (digging out a section of the plant cluster and replanting) might be effective to propagate them.

Learning about root systems and timing of growth of each species can inform vegetative propagation. This Fine Gardening article offers methods for adding plants to your garden by division. Planting in October can be successful because root growth can continue until soils cool later in the fall. There’s always room for another native plant in your garden. Garden math (seed addition or plant division) can provide those new plants. Enjoy the end of the growing season in your garden.

– Susan Carpenter, native plant garden curator