Among the many joys of feeling connected to seasonal rhythms is the way the quality of light changes over the arc of the year. Whether it is the fresh pea-green shoots of new foliage in the spring, the dappled shade under a favorite tree in the summer, or the brilliant radiance of autumn leaves, plants have a particular ability to capture and amplify sunlight.
Great garden design brings together a sense of place, color, texture, fragrance, and light. The focus of my column this week will be the concept of luminosity, and which ornamental grasses grow best in our region and excel at capturing sunlight in glittering, breezy splendor.
Observations of how light moves through your garden are crucial to help you site your perennials, trees, and shrubs in the best way possible for their growth. I like to think of light conditions as tolerances and preferences rather than requirements, keeping in mind that the plants will tell you if they are receiving too much or too little sunlight. Plants that grow in full sun will appear leggy or may not flower as well in partial sun conditions, whereas shade plants will display sunburned foliage if they receive too much direct light.
That said, planning for how light can interact with your plantings allows you to leverage luminosity to a significant effect. Ornamental grasses really excel at this task as their flowering and seedheads are naturally diffuse and diaphanous. Let us take a closer look at several genera of grasses that make excellent additions to home gardens and will captivate your attention during the golden hours after dawn and before dusk.
All grasses in our region can be divided into two groups, based on when they are actively growing and flowering: cool-season and warm-season. Most of the grasses in our lawns are cool-season, meaning they look green and lush during spring and fall but become brown during the hottest months of summer. Conversely, warm-season grasses are actively growing during summer and tend to bloom in late summer and fall.
Two excellent cool-season grasses — both native for our climate —are Wavy Hair grass (Deschampsia flexuosa) and eastern bottle-brush grass (Elymus hystrix). Wavy hair grass features very fine-textured foliage and displays thin 2-foot flowering stalks topped with silvery, pendant plumes of grass florets that catch the breeze and spring sunshine. Eastern bottle-brush grass grows taller at about 3 feet and produces wiry stems with neatly four-ranked florets that resemble its namesake, a brush to clean bottles. This is a tough grass that thrives in dry shade.
There are many choices in the warm-season group for New England gardeners, ranging from shorter growers like little bluestem (Schizachyrium scoparium) to medium-sized grasses under 6 feet. These include switchgrass (Panicum virgatum), big bluestem (Andropogon gerardii), moor grass (Molinia arundinacea), and feather reed grass (Calamagrostis x acutiflora).
Switchgrass seedhead luminosity in winter.Ulrich Lorimer
Starting with our native grasses, we will begin with little bluestem, a tough grass. Hardy and naturally growing in a pastel variety of colors, this plant tolerates average to arid soils. There are a lot of selections out there, some chosen for foliage color like “The Blues,“ others chosen for their upright habit like ”Standing Ovation.“ For best results, do not overwater or plant into rich, organic soils. Each spike features rows of tawny argent seedheads that sparkle in the light. Switchgrasses (Panicum virgatum) are equally durable, albeit larger grasses with selections ranging from 3 to 4 feet high all the way to the impressive “Thundecloud,“ which reaches the dizzying height of 8 to 9 feet when in bloom. ”Northwind” featured an upright habit, while “Shenandoah” displays gorgeous green foliage with red tips. The flowering spikes are diffuse, airy, and light brown in color.
Big bluestem (Andropogon gerardii) is found in nearly every state, a diverse and sturdy grass and keystone component of the tall grass prairie. The noticeably ornamental foliage features green, with streaks of blue, red, and purple, the flowering stalk bearing a curious turkey foot-like spikelet. There are several selections on the market with darker or redder foliage, “Blackhawks” and “Red October” respectively.
Two non-native standouts for autumn luminosity are moor grass (Molinia arundinacea), specifically a selection called “Skyracer.“ A 3-foot mound of inch-wide green strap-like foliage erupts with dozens of thin flowering stems, each terminating in a wispy seedhead of maroon florets. Fall colors include khaki brown foliage and lighter brown stalks.
The last recommendation is a well-known stalwart of the horticulture industry, and for good reason. Karl Foerster feather reed grass (Calamagrostis x acutiflora), the chief characteristic is strong, upright, sandy brown flowering spikes which erupt from a neat mound of tidy green foliage, the entire plant reaching 6 feet tall.
A postscript for this week’s column. Native Plant Trust in Framingham is celebrating a milestone this year: 125 years old. We are the nation’s first plant conservation organization and the only one dedicated to a vision of conserving and promoting New England’s native plants to ensure healthy, biologically diverse landscapes. We aim to achieve these goals through rigorous plant science, excellence in public horticulture, and engaging public programs and education.
To learn more about our commemorative gala, upcoming programs, and groundbreaking initiatives, please visit nativeplanttrust.org.
Ulrich Lorimer is the director of horticulture at the Native Plant Trust in Framingham. Send your gardening questions, along with your name/initials and hometown, to ulorimer@nativeplanttrust.org for possible publication. Some questions are edited for clarity.
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