Plants on the Front Lines: Adapting to Warmer Mid-Atlantic Summers
Spring plant research at the Mt. Cuba trial gardens
As someone who is in the position of designing other people’s gardens and home landscapes, I have an odd relationship with my own garden. If you visited my home, you wouldn’t see anything resembling anything organized or adhering to any sort of ‘proper’ design principles. It’s more like a laboratory - a testing ground to observe how some plants behave in our Zone 7b Plant Hardiness Zone. I look at growing habits throughout the season like size, bloom time, and just health in general. This year has been a bit of a shocker, with a prolonged drought laying waste to plants that are supposedly well-suited for summer heat. I’ve had to rethink some landscape choices for the future.
As the climate continues to change, plants in the Mid-Atlantic region are facing unprecedented challenges. Rising temperatures and more frequent and longer droughts are altering their habitats and pushing them to the brink. However, nature is resilient, and many plants are evolving to survive and thrive in these new conditions. And when it comes to our own landscapes, we need to adjust along with them.
Late-summer blooming Goldenrod
What Are The Challenges of a Warmer Climate?
Drought: Less rainfall and increased evaporation can create water shortages, hindering plant growth and survival.
Wilting: As plants lose water, their leaves may become wilted and droop.
Reduced Growth: Lack of water can stunt plant growth and development.
Leaf Drop: In severe drought conditions, plants may drop their leaves to conserve water.
Root Death: Prolonged drought can lead to root death, making it difficult for the plant to absorb water and nutrients.
Increased Susceptibility to Pests and Diseases: Drought-stressed plants are often more vulnerable to pests and diseases.
Seed Dormancy: In some cases, drought can trigger seed dormancy, delaying germination until conditions improve.
Pest and Disease Outbreaks: Warmer temperatures can favor the proliferation of pests and diseases that can harm plants. Warmer temperatures, during day and night, can create more favorable conditions for the growth and reproduction of many pests and pathogens. The plant’s weakened immune systems make them easier targets.
No Rest: We're also seeing higher temperatures at night, which should be a period of rest for plants, but instead they are forced to increase their respiration rates, which consumes energy that could otherwise be used for growth. As respiration rates increase, plants may have less energy available for development and weaken plants, making them more vulnerable to pests and disease.
Asclepia tuberosa, thriving on the roof of the DC Public Library
Plant Adaptations to a Changing Climate
Despite these challenges, many plants have developed strategies to cope with rising temperatures and drought conditions:
Drought Tolerance:
Succulents: Plants like Sedum and Stonecrop have developed fleshy stems or leaves to store water.
Deep Roots: Plants with deep roots can access water from underground sources, even during dry periods.
Waxy Leaves: A waxy coating on leaves helps to reduce water loss through transpiration.
Heat Tolerance:
Shade-Loving Plants: Plants that prefer shady areas can avoid the direct heat of the sun.
Smaller Leaves: Smaller leaves can reduce the surface area exposed to the sun, minimizing heat stress.
Hairy Leaves: Hairy leaves can trap air, creating a microclimate that helps to cool the plant.
Early Flowering: Some plants have shifted their flowering times to earlier in the spring, allowing them to complete their life cycles before the hottest part of the summer.
Winners and Losers
Not all plants are created equal when it comes to adapting to climate change. Some species are thriving in the new conditions, while others are struggling to survive.
Winners:
Native Grasses: Many native grasses, such as Little Bluestem and Panicum, are well-suited to drought conditions and can tolerate high temperatures.
Succulents: Plants like Stonecrop are naturally adapted to arid environments and can thrive in the Mid-Atlantic's increasingly dry summers.
Invasive Species: Unfortunately, some invasive plants, such as kudzu, Tree of Heaven, and Japanese honeysuckle, are also highly adaptable and are spreading rapidly in the region.
Losers:
Shade-Loving Trees: Trees like American beech and sugar maple, which prefer cool, moist conditions, are particularly vulnerable to heat stress and drought.
Wetland Plants: Species that rely on consistent moisture, such as cattails and water lilies, may be threatened by declining water levels.
Forest Understories: The delicate plants that grow beneath the canopy of forests are often susceptible to drought and can be outcompeted by invasive species.
As the climate continues to change, it is essential to understand how plants are adapting and to support conservation efforts to protect vulnerable species. By studying plant adaptations and developing sustainable land management practices, we can help to ensure the survival of our region's diverse plant life.
When selecting plants for a hotter, drier climate, it's essential to prioritize drought-tolerant species. Look for plants with features like deep roots, succulent leaves, or small, leathery foliage that minimizes water loss. Consider native plants, as they are often well-adapted to the local climate and require less maintenance. Additionally, choose plants with a low water demand, such as Sedum/Stonecrop, and drought-tolerant grasses. Avoid plants that require frequent watering or thrive in moist conditions.
“when it comes to our own landscapes, we need to adjust along with them”
Ok let’s get to the specifics. What’s in an expert’s personal list of plants to use for a summer-hardy landscape? Here’s a working list, which is always being updated. And for brevity’s sake, this is for summer-blooming, native perennials and grasses i.e., no need to include spring bloomers like Creeping Phlox, Baptisia, Columbine, etc. as they should still, as of now, get a more conducive spring climate.
Coreopsis, Tickseed
Vigorous perennial blooming from late spring through fall, depending on the cultivar, so be sure to know which kind you have. The flowers are continuous, uniform, and thrives in heat and sun, and drought resistant.
Go-to Cultivars: Moonbeam, Zagreb
Rudbeckia, Black-Eyed Susan
Popular perennial with showy, daisy-type yellow flowers with a black center. Long-blooming and popular for pollinators;
Go-to Cultivars: Goldsturm, American Gold Rush
Echinacea, Coneflower
Immensely popular and long-blooming native pollinator; blooms profusely for two months; Many different cultivars in a variety of colors
Go-to Cultivars: Magnus, Kismet series
Gaillardia, Blanketflower
Compact perennial that forms a tidy mound of grayish-green leaves and long-lasting red flowers with a yellow border. A magnet for butterflies and makes good cut flowers.
Go-to Cultivars: Arizona Sun
Asclepias tuberosa, Butterfly Weed
Bushy perennial with orange flowers that bloom throughout the summer; abundant foliage and critical to the monarch butterfly population; a great plant for pollinators in general
Go-to Cultivars: [straight species]
Monarda, Bee Balm
Blooms in the high heat of summer and attracts bees, butterflies, and hummingbirds; Comes in a variety of colors, including lavender, scarlet red, and pinkish
Go-to Cultivars: Jacob Cline, Claire Grace
Liatris, Blazing Star
Drought tolerant when established; Has deep roots to find moisture; Attractive to bees, birds, and butterflies; deer resistant and disease-free
Go-to Cultivars: Kobold
Pycnanthemum, Mountain Mint
Clump-forming perennial which have mint-scented leaves when crushed. Tubular pink flowers in mid to late summer. Should have some shade but is drought- and heat-tolerant. Attractive to pollinators.
Go-to Cultivars: [straight species: Pycnanthemum muticum]
Sedum/Hylotelephium, Stonecrop
Upright with clusters of deep pink flowers. The foliage is fleshy, grey-green and is long-blooming. Drought tolerant and attracts butterflies.
Go-to Cultivars: Brilliant, Autumn Joy
Yarrow, Achillea
Part of the aster family, Yarrow's large root system help it survive in dry conditions by reducing transpiration. It can also survive on natural rainfall and doesn't need much additional watering once established.
Go-to Cultivars: Moonshine, Coronation Gold
Agastache, Anise Hyssop, Hummingbird Mint
Drought and heat tolerant and attractive to pollinators, they are best in sunny locations and are low-maintenance when established.
Go-to Cultivars: Blue Fortune
Phlox paniculata, Summer Phlox
Fragrant flowers grow on stiff stems throughout the summer; A classic garden plant that attracts birds and butterflies; Thrives in most any semi-fertile well-drained soil.
Go-to Cultivars: Jeana, Nicky
Solidago, Goldenrod
Long-blooming sprays of yellow flowers grow in late summer; Bees will actually sleep in its flowers! Needs plenty of room because it will spread.
Go-to Cultivars: Fireworks, Little Miss Sunshine (less aggressive)
Schizachyrium, Little Bluestem
Lovely drought-resistant grass that has an extensive, deep root system, allowing it to do well on poor soil
Go-to Cultivars: Standing Ovation, Chameleon (smaller size)
Panicum, Switchgrass
Warm-season prairie grass that is drought tolerant and not picky about soil. This workhorse can be used ornamentally and is easy to grow.
Go-to Cultivars: Heavy Metal, Shenandoah, North Wind
Juniperus horizontalis, Creeping Juniper
A low-growing evergreen shrub that is commonly used in dry regions and as a low groundcover; Thrives in hot summer climates and isn’t picky about soil.
Go-to Cultivars: Blue Rug, Wiltonii
Here are a few non-natives that are also useful:
Stachys, Lamb’s Ear
sun-loving perennial plant grown for its thick, fuzzy, silvery foliage that creates a soft-textured mat in the garden; spreads readily and drought tolerant
Go-to Cultivars: Helene von Stein
Lavandula, Lavender
A mainstay of herb gardens. Purple flowers appear in terminal spikes in late spring to early summer. Both foliage and flowers are highly aromatic.
Go-to Cultivars: Hidcote
Perovskia, Russian Sage
Bushy perennial with long panicles of lavender-blue flowers and gray-green leaves; virtually pest and disease-free
Go-to Cultivars: Blue Jean Baby
A selection from this list would make a fine summer garden for full sun. Mix in a few evergreen shrubs and you’ll have the makings of a resilient landscape that will thrive in rising temperatures. Always feel free to consult with local gardening experts or nurseries to get specific recommendations for your region.
