Richard Hawke – My Chicago Botanic Garden

What Are the Best Plants for Your Midwestern Garden?

I put together my top five picks for all-around Best Midwest plants after being contacted by editors at Midwest Living magazine.

Polling a number of experts in the Midwest, the editors asked for recommendations of award-worthy plants and then came up with a list of great plants that gardeners can count on. (I was happy to note some of the winners are proven perennials from the Chicago Botanic Garden’s trials, as well as plants I’ve grown and loved for a long time.)

Here’s my shortlist—including one with crazy beautiful flowers and one that’s so easy to grow that you basically just plant it in the right spot and water it.

See the plants that made it on to the Midwest Living list.

Best for Sun

‘Joanna Reed’ catmint (Nepeta ‘Joanna Reed’) is one of the tidiest catmints I’ve ever grown, an attribute that cinched a top rating in our trial. The strong stems never flopped and new shoots grow quickly to conceal the declining flowers stems, thus eliminating the need for deadheading. Compact, wide spreading plants (24 inches tall and 48 inches wide) are covered with a continuous display of violet-blue flowers from spring into fall; if you’re thinking that means loads of pollinators, you’d be right! The aromatic, dusty green leaves are not only attractive but also unpalatable to deer—a bragging point shared by many catmints.

Lamb's ears (Stachys byzantia) and catmint (Nepeta) in the Garden. — Fuzzy lamb’s ears (*Stachys byzantina*) pair well with catmint (*Nepeta*—in the background).

To me, lamb’s ears (Stachys byzantina) is an essential perennial for sunny gardens and ‘Big Ears’ is my favorite. Its large, pale silvery-green leaves are velvety soft and the perfect color and textural foil for other perennials—it looks good with both hot- and cool-colored flowers. ‘Big Ears’ is a shy flowerer; in fact, it is touted as non-flowering. Occasionally, a fuzzy flower stem or two pops up with tiny purple flowers hidden in woolly clusters. Low growing and spreading (14 inches tall and 30 inches wide), ‘Big Ears’ is a great groundcover or massing plant. Both of these sun-loving perennials like well-drained soils and are tolerant of hot, dry conditions.

Best Native Plant

Butterfly weed (Asclepias tuberosa) makes my list of best native plants because its flowers are crazy beautiful, and it might just be one of the most important plants of the day. Honestly, the eye-catching bright orange flowers are reason enough to love this plant, but the fact that they attract a myriad of butterflies, including the beloved monarch, makes them invaluable. The survival and success of the monarch butterfly is tied directly to butterfly weed—the caterpillar feeds on the leaves and the adult butterfly on the nectar. Butterfly weed is a great garden perennial in formal and naturalistic plantings, and because it is commonly seed-grown, flower color varies from orange to yellow to nearly red. The Perennial Plant Association named Asclepias tuberosa the 2017 Perennial Plant of the Year.

Best Annual

Black and Blue sage (Salvia guaranitica 'Black and Blue') — Black and Blue sage (*Salvia guaranitica* ‘Black and Blue’)

I haven’t evaluated annuals in more than 20 years, and I don’t personally grow many annuals. However, I’m a huge fan of tender sages—so much so that we started a trial of 105 different nonhardy sages last year. Salvia ‘Black and Blue’ has been around for a while and has proven to be a phenomenal plant for seasonal displays in containers and garden borders. The combination of cobalt blue flowers and near-black calyces and stems is stunning. It blooms from midsummer to frost and attracts hummingbirds, butterflies, and bees aplenty. ‘Black and Blue’ is a rapid grower, reaching 2 to 4 feet tall and 1 to 3 feet wide in a summer, and is best suited to sunny locations.

Best Plant-It-and-Forget-It

Hosta sieboldiana 'Elegans' — *Hosta sieboldiana* ‘Elegans’

Hostas are quintessential plant-it-and-forget-it perennials. Long-lived and easy-care, hostas come in a wide variety of colors, forms, and sizes. Success is as simple as providing them with adequate water and planting them in partial to dappled shade. Hosta sieboldiana ‘Elegans’ features thick, corrugated blue-green leaves and near-white funnel-shaped flowers in early summer. ‘Elegans’ is robust at 30 inches tall and 48 inches wide, with heart-shaped leaves more than a foot long. Hostas rarely, if ever, need division—I have a big planting of ‘Elegans’ in my home garden that has been in place for more than 20 years with no care beyond removing the old leaves in the spring.

The Sky’s the Limit

When the Green Roof Garden was first planted in 2009, everything we knew about long-term rooftop gardening was theoretical. Which plants would live more than one year on the roof? No one knew for sure. Were native plants better to plant than non-natives? Unknown. What about soil depth, extreme weather, pests, diseases? The list of questions was long.

Download An Evaluation Study of Plants for Use on Green Roofs here.

Download the results of this 5-year study. Click here.

Today, after five years of watching, waiting, documenting, and evaluating, we now have actual data to guide us—and others—on the ever-more-popular topic of green roofs! I’ve just published the Plant Evaluation Notes from our research—the first national plant evaluation study of its kind.

Among the data are a few surprises.

The biggest surprise may seem the most obvious—it’s that the green roof survived as well as it did!

I was blown away by the survival rates among plants, and by the fact that so many of them thrived and even excelled in such a challenging landscape. Of the more than 40,000 plants that we installed on both roofs, 30,568 of them were still alive in 2014. Just 14% of the 216 taxa died—that’s a pretty good success rate when you consider rooftop conditions. In fact, adaptability was one of the main criteria that we evaluated each plant on. Here’s the five-point list:

Adaptability (to hot/cold, dry, windy conditions, plus shallow soils)
Pests/diseases
Winter hardiness
Non-weediness
Ornamental beauty

Other surprises? Definitely the wild white indigo (Baptisia alba var. alba). Although I didn’t expect it to fail, I also didn’t expect it to be as large and vigorous as it has become. By year five, it was nearly three feet tall, with dramatic spires of white flowers. Meadow blazing star (Liatris ligulistylis) was in the same elegant category. But the absolute standout was prairie dropseed (Sporobolus heterolepis). It looked good all year, at all soil depths, and the fragrant flowers made the roof smell like popcorn in August and September.

PHOTO: Antennaria dioica. — *Antennaria dioica*

PHOTO: Baptisia alba var. alba. — *Baptisia alba* var. *alba*

PHOTO: Phlox subulata 'Emerald Blue'. — *Phlox subulata* ‘Emerald Blue’

PHOTO: View of the Green Roof Garden from above. — The Green Roof Garden today: a tapestry of plant life

It also surprised me that some of the drought-tolerant plants like sulfur flower (Eriogonum umbellatum), tufted fleabane (Erigeron caespitosa), and long-petaled lewisia (Lewisia longipetala ‘Little Plum’) didn’t do better on the green roof. Same goes for sundial lupine (Lupinus perennis). In a broader sense, I’m disappointed that we haven’t had greater success with plants in the shallowest, 4-inch soil depth. It’s the most challenging area on the green roof, so we’ll strive to add more types of plants to this trial area in the coming years.

Monitoring plants in the field

Top 10 Performers
on the Green Roof

Pussytoes (Antennaria dioica)
Dwarf calamint (Calamintha nepeta ssp. nepeta)
Juniper ‘Viridis’ (Juniperus chinensis var. sargentii ‘Viridis’)
Creeping phlox ‘Emerald Blue’ (Phlox subulata ‘Emerald Blue’)
Creeping phlox ‘Apple Blossom’ (Phlox subulata ‘Apple Blossom’)
Creeping phlox ‘Snowflake’ (Phlox subulata ‘Snowflake’)
Aromatic sumac ‘Gro-Low’ (Rhus aromatica ‘Gro-Low’)
Prairie dropseed (Sporobolus heterolepis)
Prairie dropseed ‘Tara’ (Sporobolus heterolepis ‘Tara’)
The 69 other plants that got four-star ratings (good)!

What else is coming to the Green Roof Garden?

We’ll bring in a new set of plants (both native and non-native) to be evaluated and increase the replication of trials in 4-, 6- and 8-inch soil depths. Our goal is to compile a broad list of proven plants so that anyone—businesses, architects, governmental groups, and residential homeowners—has the information they need to grow a green roof. The sky’s the limit!

Visit the Green Roof Garden at the Daniel F. and Ada L. Rice Plant Conservation Center—open ‘til 9 p.m. all summer. The garden has two halves: the Ellis Goodman Family Foundation Green Roof Garden South and the Josephine P. & John J. Louis Foundation Green Roof Garden North.

Three Years of the Green Roof Garden…and Counting

It’s hard to believe that the Green Roof Garden has been in place for three full growing seasons already. Our horticultural and research staff is pleased to see how the green roof is growing and evolving as plants settle in and move around by rhizomes and reseeding. Despite the challenging weather of 2011 and 2012, the vast majority of the 240 taxa currently on the green roof have thrived. While our goal is to minimize the care and resources put into maintaining the roof, we had to give the plants supplemental water once in July 2011 and twice in June 2012 during periods of extreme heat and drought. Not surprisingly, the greatest stress was on plants in the shallow 4-inch-deep plots. But the great news is that plants rebounded quickly once they received the additional water.

PHOTO: Aerial view of the PCSC green roof garden — The Plant Conservation Science Center Green Roof Garden

The Green Roof Garden contains a mixture of plants that are commonly grown on green roofs and other taxa that are uncommon or untested for this use. The plant evaluation component is a particularly exciting aspect of our green roof—fully half of the 16,000 square feet is dedicated to testing a broad variety of new plants for green roof culture. In a way, the sky’s the limit on what we can try. In fact, we initiated a new trial of prickly pear cactus (Opuntia spp.) in 2012 to see how these succulents from the western U.S. perform next to our local species, Opuntia humifusa.

PHOTO: Common mountainmint (Pycnanthemum virginianum) — Common mountainmint (*Pycnanthemum virginianum*)

There have been many success stories on the roof, but here are just a few native plants that I’ve found particularly strong performers in 2012:

Common mountainmint (Pycnanthemum virginianum) is native to eastern North America and found in dry and moist prairies and calcareous fens in the Chicago region. Plants remained ornamental and healthy regardless of droughty conditions; it is growing in the semi-intensive 8-inch substrate depth. While stress caused lower leaves to drop, plants flowered well and maintained strongly upright habits at all times. Plants were 22 inches tall and 10 inches wide in 2012 and the small white flowers were in bloom from early July to late September. Bees, moths, wasps, and flies are frequent visitors on common mountainmint.

Although pitcher sage (Salvia azurea var. grandiflora) is an introduced plant in the Chicago region, it is native to dry prairies in Illinois. Pitcher sage features exceptional sky blue flowers from late summer to frost. A serendipitous planting of pitcher sage, stiff goldenrod (Solidago rigida), and big bluestem (Andropogon gerardii) made a spectacular show last year. We’re growing pitcher sage in extensive to semi-intensive plots so flowering stems ranged from 30 inches tall in the 4-inch plots to 56 inches tall in the 8-inch plots.

PHOTO: Pitcher's sage (Salvia azurea var. grandiflora) — Pitcher’s sage (*Salvia azurea* var. *grandiflora*)

PHOTO: Stiff goldenrod (Solidago rigida) — Stiff goldenrod (*Solidago rigida*)

PHOTO: Big bluestem (Andropogon gerardii) — Big bluestem (*Andropogon gerardii*)

Prairie dropseed (Sporobolus heterolepis) and the cultivar ‘Tara’ are being grown in the extensive to semi-intensive plots. Variable plant sizes, from 14 to 40 inches tall and 26 to 40 inches wide, were observed in the different plots. Leaves remained green throughout the growing season, even in droughty conditions, and turned a beautiful orange in autumn. The pungently fragrant flowers opened in August and remained effective for many weeks. Prairie dropseed is native to mesic and hill prairies in Illinois. ‘Tara’ is generally shorter than the species by about a foot and has darker green leaves and a vase-shaped habit.

PHOTO: Arrowleaf violet (Viola sagittata) — Arrowleaf violet (*Viola sagittata*)

Arrowleaf violet (Viola sagittata) naturally occurs in sandy old fields and dry prairies in the Chicago region, and is known to occur in sterile abandoned clay fields where the topsoil has been eroded off. Given its adaptability to poor soil conditions, arrowleaf violet was recommended for testing by Jim Steffen, one of the Garden’s ecologists. Arrowleaf violet bloomed from early April to early May and then again later in the summer. It is a generous re-seeder and has begun to pop up around the Green Roof Garden. Plants are grown in extensive to semi-intensive plots, but greater vigor has been noted in 6 inches of growing media than in 4 inches.