Earlier this spring, weather was cool or even cold for May in Minnesota. Hard to recall with the current endless 90 degree days. But blue oat grass, Helictotrichon sempervirens, remembers and grew very well in those cool days. Native to alpine regions in southwestern Europe, this grass likes cool temps and well drained or dry sites. The first photo below was taken June 8, 2021 at the Minnesota Landscape Arboretum. Note the robust icy blue foliage from the cool days in the previous month and even a few flowers.
The best flowers I have ever seen on blue oat grass plants were growing in Vail, Colorado, second photo below, where the days are almost always cool. These images almost look like two different grasses!
Shade tolerant vigorous plants are useful for tough sites in the garden. Two non-native sedges that are hardy and rhizomatous are black-flowered sedge Carex nigra ‘Variegata’ and Carex flacca ‘Blue Zinger’, blue sedge. Flowers appear early on these two sedges, shown here on May 18, 2021. Seedlings have not been found in Minnesota from these plants, but their strong rhizomes are not to be underestimated in a garden setting. Plant with care in a location that needs a rhizomatous plant.
With the new information that native skipper butterfly larva overwinter at the base of native grasses, we cut these plants back in the spring at the Minnesota Landscape Arboretum instead of burning. We leave about 6 inches at the base of the plants. The tops go into compost or are burned. Little bluestem shown below, grows better after a burn, perhaps due to drying out the crown and reducing fungal pathogens. A tradeoff: cutting back favors pollinators, burning favors the grass plants.
Gardening with Native Grasses in Cold Climates is now available through the University of Minnesota’s Press Books. With help and guidance from University of Minnesota librarian Kristen Mastel, authors Diane M. Narem and Mary Hockenberry Meyer released the new digital version of this book in November 2020.
Gardening with Native Grasses in Cold Climates and a Guide to the Butterflies They Support was originally published in May 2018. The previous version was only available on Apple platforms, limiting who could access the information.
The new version is available for free from the University’s digital library collection. You can download the entire book or read it online.
The book is divided into five chapters:
Introduction to Grasses
Benefits of Native Grasses
Common Native Grasses of the Northern Midwest
Planting, Maintenance and Management
Grass Selection and Butterfly Pairings
Gardening with Native Grasses in Cold Climates, is written for inexperienced as well as seasoned gardeners, landscape designers, garden center employees, and anyone interested in native grasses that grow well in cold climates. New information on the benefits of native grasses including their importance as host plants for native Lepidoptera is included. Combinations of specific grasses used by larvae and perennials that the adult butterflies feed on is new and timely information.
Information in the book is based on research conducted by Narem and Meyer. Tables, plant lists and numerous illustrations are also included.
The 2019 USDA Census of Horticulture Specialities is complete and figures for ornamental grasses were $178,791,000 in sales for 1,991 businesses. Grasses continue to grow in sales, up 13% from $158,061,021 in 2014, and $124,261,118 in 2009. In 2019 Florida had the top sales with more than $11M, followed by California with $7.5M. Eights states sold between $1 and 2 million in ornamental grasses: Alabama, Georgia, Louisiana, Maryland, Michigan, Ohio, Oregon and Texas. Grasses continue to increase as important landscape plants.
Early spring is time to clean up grasses. Dale Nemec at Scott Arboretum at Swarthmore College has a good video of how he cleans up the grasses in the spring. He uses a variety of tools on several different grasses. Spring cutback means more vigorous plants. Minnesota Landscape Arboretum gardeners sometimes use a mower set high to clean up sedges as shown below.
Northcreek Nurseries recently made the decision to stop selling Carex flacca, blue or carnation sedge, due to information from botanist Dr. Robert Naczi of New York Botanic Garden that Carex flacca is spreading beyond the garden. Also know or sold as ‘Blue Zinger’, Carex flacca is native to Europe but has been documented in Canada and the U. S. as early as 1894. Northcreek is recommending replacing C. flacca with similar blue-foliage native Carex species, such as Carex flaccosperma, Carex platyphylla, or Carex laxiculmis Bunny Blue® ‘HOBB’.
In Minnesota, Carex flacca has not been invasive beyond where it is originally planted. It does have significant rhizomes, which are certainly something to consider when planting this zone 4 winter hardy, almost evergreen ground cover. The planting below shows a great use of Carex flacca on a steep slope in late March at the Minnesota Landscape Arboretum. Some years, if the foliage is more brown than green in early spring, gardeners mow off the plants with lawn mower blade set at 4 inches.
This close up of blue-green sedge shows its dense foliage with blue-green coloration. We will continue to monitor this plant for invasiveness and report any further findings in Minnesota at this website. We appreciate Northcreek sharing their information so all gardeners can be aware of changes in plants in managed and natural landscapes.
Heavy wet snow can knock down the biggest of grasses. But Molinia ‘Karl Foerster’ below, with its pencil-thin stems was not affected. Still green and growing on Oct 22.
Look at the ‘skirt’ surrounding the standing center of giant miscanthus at the Minnesota Landscape Arboretum. This snow came on October 22, with thunder and much moisture that snapped the bamboo-like stems of giant miscanthus. Note the green tops, as the plant was not dormant.These stems did not recover after the snow melted, but if the stem is not broken, grasses can rebound after some snow.
Because switchgrass, Panicum virgatum, is native to almost every state in the U. S. it has a wide variation of growth habits and forms. Shown above are newer forms, from the left, Bad Hair Day, Purple Tears, Blue Fountain, and Apache Rose on Sept 17, 2020 at the Minnesota Landscape Arboretum Grass Collection.