Sustainable enough

I just listened to an informative interview with Uli Lorimer, director of horticulture at Native Plant Trust, our local native plant society in Framingham, Massachusetts. Uli was a guest on garden writer Thomas Christopher’s weekly radio show and podcast, Growing Greener. Thomas focused the interview on native and locally adapted plants.

Monarch on New England aster

    Together, the two men proposed a type of garden that’s designed to serve the interests of as many living things as possible, not just humans. Instead of choosing plants because they’re pretty, you’d select what performs the most useful functions for your garden ecosystem. You’d put aside neatness as a top aesthetic priority.

Goldenrod is a key player in this meadow ecosystem in Maine

    This is the path I want to follow, but I argue that we don’t all have to arrive right away. Uli pointed out that much important information about native plants hasn’t yet been ascertained, and the rest hasn’t spread past native plant enthusiasts. As a start, he suggested, growers should be using plant labels to tell where plants came from and how they were propagated.

A plant label that lists the seed source and nursery location

    Native Plant Trust advocates growing plants that evolved in the local ecoregion, the area with the same environmental conditions they'll find in your garden. In addition, they value genetic diversity within each species, meaning plants that are grown from seed, not cloned through cuttings or divisions to be genetically identical. 

    A genetically diverse, locally adapted plant population will be well-equipped to deal with shifts in its environment, including rapidly changing climate. But so far, conventional growers haven’t figured out how growing from seed could be scaled up to their volume of production in a financially viable way. In addition, we consumers have been trained to want reliably uniform plants, which is what you get with clones. Seed-grown plants are variable. 

Mass produced plants are genetically identical and uniform

    Native Plant Trust sells about 300 species of locally adapted native plants at their garden shop. They’re grown from ethically collected wild seed of known New England provenance. But what if the shop doesn’t offer a native plant you’d like to buy? Is it wrong to buy plants that don’t meet their high standards?

    This brings me to my point. I think becoming a sustainable gardener, and a native plant gardener, can be a process. You don’t have to change everything all at once. After 35 years, my garden is full of nonnative plants I’ve chosen over the years. Many of the ones that have survived are plants I love and wouldn’t dream of removing. We have a history together.

They'll have to pry my nonnative white bleeding heart from my cold dead trowel

    Every year as I learn more about native plants, I add more of them to the garden. I adjust my gardening approach to accommodate their needs and welcome a richer population of wildlife, especially insects. Is it still OK to buy nonnative plants because you like them, or North American native plants even if they’re not local, they’re “improved” cultivars of native species, or they’ve been propagated asexually? I think it is. If we’re thinking about these issues, we’re moving toward full sustainability, even if we’re not there yet.

Newly planted mountain mint from NPT--native, locally grown and adapted

 

Choosing between cultivars

Despite my recent interest in planting straight native plants, I’ve got lots of cultivars in my garden and expect to bring home more in future. Cultivars are improved versions of a species, selected or bred for desirable characteristics such as bigger flowers or new flower colors. Cultivars of native species are sometimes called “nativars.”

This coneflower, Echinacea 'Sundown', is a nativar-photo Mike Peel

    I’m used to thinking that cultivars are selections culled from nursery beds or native plant populations by sharp-eyed growers. But this is only one of the paths to a market-worthy cultivar, I’ve learned. Other cultivars are the products of intentional breeding programs. Once they’ve been found or developed, cultivars will be propagated asexually, through cuttings or divisions, so that the offspring will be exactly like the parent. That means they won’t add genetic diversity to your landscape, as native species will.

    At a recent garden club meeting, a member asked me whether her white-flowered coneflower cultivar counts as a native for the purpose of attracting desirable insects. It’s an important question and an area of active research. Recording native pollinator visits to flowering phlox plants, both straight natives and cultivars, Keith Nevison, a researcher at Mt. Cuba Center in Delaware, was surprised to find that a cultivar, Phlox paniculata ‘Jeana’, attracted the most pollinators. He hypothesized that this might be because ‘Jeana’ blooms so generously and has small, shallow flowers that are easy for pollinators to use.

Tiger swallowtail on Phlox 'Jeana'-photo Michele Dorsey Walfred

    Similarly, the Nativars Research Project of the Chicago Botanic Garden used citizen scientist observations through project Budburst to determine that cultivars vary widely in their attractiveness to pollinators. Among beardtongues (Penstemon digitalis), for example, popular cultivars ‘Husker Red’ and ‘Blackbeard’, loved for their deep purple foliage, drew far fewer insects than ‘Pocahontas’. 

Penstemon 'Pocahontas' at Bluestone Perennials

Scientists suggest that the difference is in the origin of the plants. ‘Pocahontas’ was discovered in the wild. That’s something it has in common with Phlox ‘Jeana’, which was found growing wild outside Nashville. Apparently when plants change in the wild, the new genetic mixes that survive are the ones that cooperate successfully with local insects.

    Some early guidelines seem to be developing for gardeners who want to pick plants to benefit pollinators. Cultivar flowers that resemble the native’s most closely are more likely to attract insects than blooms that have been radically altered in the breeding process.

Echinacea 'Razzmatazz' is probably too different from its straight native ancestor

And now we can surmise that wild-selected cultivars are also more likely to be popular with pollinators than cultivars produced by human breeding efforts. Much more research will be needed before we can be sure which cultivars to plant for pollinators.

    So what about that white-flowered coneflower? Where did it come from? I see that Echinacea ‘White Swan’ may have been introduced by Piet Oudolf, the legendary Dutch garden designer. Did he find it growing in his garden? I can’t tell.

Piet Oudolf border, Royal Horticultural Society Garden Wisley, with white coneflower bottom right-photo Esther Westerveld

    Growers introduce lots of new cultivars of native plants every year. Right now, I think the only way we can determine which ones are most popular with pollinators is to plant them and observe.