New perennials the easy way

To share purple coneflowers (Echinacea purpurea) with students in last month’s sustainable gardening course, I asked them to snip off the spiky brown heads of the coneflowers in the flower bed. Just drop those dried-up brown items on the ground, I confidently told them, and they’ll plant themselves.

    The reason I believed this would work was that the same method had succeeded for me. I’d purchased and planted a single potted coneflower. When I wanted to make more, I initially thought I’d have to divide the plant, cutting out a section of its stems and roots. Or I’d have to collect seeds, plant them indoors, and grow them to transplanting size under lights. 

Goldfinch feeding on coneflower seeds

    But there were so many of the “cones,” that I decided to try dropping some where I wanted new plants and see if something would grow. This worked surprisingly well, and now I have a line of coneflowers where I scattered those seeds. 

A patch of coneflowers has grown where I dropped seedheads in fall

The round seedheads are what’s left after the flowers are pollinated, seeds develop from each of the mini-flowers in the central globe, and the petals drop off. If pollinators are around to do their work, each cone can carry hundreds of seeds.

Each spike is a coneflower seed

    Some native flowers grow easily from scattered seeds. Black-eyed Susans (Rudbeckia hirta) do this every year in my insectary bed. This plant is a biennial with a lifespan of two years. It performs like a perennial, though, because the seeds that drop from the flowers grow into next year’s flowering plants. If you didn’t know, you’d think the parent plants lived on indefinitely. I write about these plants a lot because they’re among my most successful and lowest maintenance natives.

    Last year I attended a lecture on how to grow native perennials from seed. This is a way to create a genetically diverse plant collection, because seeds combine the genes of both parents. I learned that the process is much more complicated than what I’m used to with annuals and vegetables. Some perennial seeds need a period of sustained cold, which in nature would be provided by winter. Some need alternating warm and cold treatment. Some need help breaking through hard seed coats.

Trillium seeds require several cold and warm seasons before they'll germinate-photo Finetooth

    These perennials have evolved strategies to delay germination until the conditions are right. That’s how they maximize viable offspring and avoid being destroyed by animals or shouldered aside by other plants vying for the same sites and resources. But imitating the sequence of events that triggers germination in many native perennials would be tough, exacting work.

    The alternative is to let the process happen outdoors without intervening. Since I don’t need to produce large numbers of plants, I can let nature do the work. I’ve stopped reflexively dead-heading, removing flowers before they can set seed. I’m hoping that seeds of some of the new native perennials that flowered in my garden this year, including sweet goldenrod (Solidago odora), Stokes’ aster (Stokesia laevis), and blue-eyed grass (Sisyrinchium angustifolium) will surround their parents with the beginnings of small colonies next spring.

Blue-eyed grass flowering in June