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Extension > Garden > Yard and Garden > Landscaping > Ornamental grasses for cold climates

Introduction

By Mary Hockenberry Meyer, University of Minnesota
Copyright © 2012 Regents of the University of Minnesota. All rights reserved.

NOTE: This is an excerpt adapted from Ornamental Grasses for Cold Climates. Order a copy or find more information at the Landscape Arboretum.

Grasses add beauty and interest to the garden while providing important ecological benefits and diversity to the landscape.

Their dramatic change through the seasons adds a new dimension to the garden with an informal, natural appearance. Information in this book is based on 25 years of field research results from multiple locations in Minnesota.

The objectives of this publication are to provide accurate information on the culture, landscape features, and special uses of native and non-native grasses and increase appreciation for this diverse family of plants. Botanically speaking, the sedge family is also included, as are a few rushes. This information will help gardeners, nurseries, garden centers, landscape designers, and homeowners who live and garden in the northern or colder climates of the United States.

from left: oriental fountaingrass; feather reedgrass; switchgrass

Features of grasses

Research

Image 1: Research locations and years of field hardiness trials

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Image 1: Research locations and years of field hardiness trials

  • Morris, Crookston, 1996–2003
  • St. Paul, 1987–1998
  • Minnesota Landscape Arboretum, 1987–continuing

The information in this publication is based on University of Minnesota research conducted from 1987 to present in sites throughout the state (see image 1).

Culture and maintenance

Ornamental grasses can be planted in spring, summer, or fall. Spring planting represents the least risk and is the only time to plant bare rooted grasses. Supplemental water may be necessary for summer plantings. In the fall, plant only container plants with well established root systems and allow for at least one month of growth before winter.

Determine spacing needs according to the desired landscape effect and the plant's setting. A good rule of thumb is to space plants equal to their mature height (plants 4' tall are spaced 4' apart), but you can plant farther apart for specimen plants, or space plants one-half their height for a hedge or screen.

Division (digging up the plant and cutting it into smaller sections, each with stem and roots) is the most common method of propagation. Named cultivars can only be increased by vegetative propagation and will not come true from seed. Some grasses can be propagated with stem cuttings, such as purple fountaingrass and Miscanthus. Lower nodes on the stem are the most successful for cuttings. Seed propagation is typical for prairie restorations and for areas where diversity is desirable.

Large mature grasses may benefit from spring division, especially if the center of the plant is dead. This may be a major job, requiring a strong back and a sharp spade. Division is not a requirement of grasses; however, a need for more plants, an obvious dead center, or poor vigor are reasons to divide a plant. If you find a grass is declining and flowers are few, division may be helpful in rejuvenating the plant. Calamagrostis ×acutiflora 'Karl Foerster' can successfully be divided in the fall, but most other grasses respond best to spring division.

In late winter or early spring, before new growth starts, cut back grasses to the ground to remove the previous year's growth. If the plants are not cut back, spring growth can be delayed and large plants will look unattractive (half dead) throughout the year. Manual trimming with an electric hedge trimmer works well for small areas. Large areas can be burned, if permitted and closely supervised, or mowed. In our research, the grasses were burned to the ground, usually in April. Some cool season grasses and sedges may be semi-evergreen such as Deschampsia, Festuca, Helictotrichon, and Carex 'Ice Dance,' and should be carefully cut back or any dead foliage and flowers removed with a rake or by hand. Burning cool season grasses may be fatal. Calamagrostis ×acutiflora 'Karl Foerster' begins to grow very early in spring and can be cut back in March or early April.

Cutting back grasses in the fall, especially younger plants, may result in winter injury and the beauty of the plants in the winter landscape is lost. Trimming plants to 1–2 feet can be a compromise to maintain a tidy appearance and still hold leaves and snow for winter protection.

Soil

In our field research plots, the soil pH varied from 7.2–7.8. Soils were loamy clays and glacial lakebed with high organic matter and water holding capacity. Many ornamental grasses will grow well on a wide variety of soils with a pH range of 5.0–8.0. Established grasses rarely need fertilization or irrigation except in cases of extreme drought or very sandy soils. In our research, an organic wood chip mulch was applied annually to prevent weeds.

Pests

Hand weeding, or spot treatment with a contact herbicide for persistent weeds such as quackgrass, was part of routine maintenance in our research plots. Rust was occasionally noted on Deschampsia and Calamagrostis but no pesticide was applied and other than weeds, no additional pests were noted on the plantings. Deer and rabbits had access to all these plantings. Rabbits occasionally ate Hakonechloa; no deer browsing damage was seen on the grasses.

Cool and warm season grasses

Image 2: Cool and warm season grass growth chart

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Image 2: Cool and warm season grass growth chart

Most grasses fall into cool or warm season growing patterns (see image 2). Cool season grasses green up and begin to grow early in spring, produce flowers in late spring or early summer, may be dormant in summer especially in times of drought or high temperatures, and resume growth again in fall. Late summer and fall is an important time for root growth in cool season grasses. The contrasting green basal foliage and taller beige or tan flowers of cool season grasses give these plants an interesting appearance.

Warm season grasses are slow to begin growth in the spring, flower in late summer and fall, grow actively in heat or summer conditions, and are often drought tolerant. Growing both warm and cool season grasses will add a diversity of flowering times and interest to your garden and landscape.

Most grasses prefer full sun. Our research plantings were in full sun, except for one section under shade at the Minnesota Landscape Arboretum. Grasses and sedges that tolerate shade are listed on page 40.

Grasses can grow in difficult landscape settings, such as on slopes, along lakeshores, as screens, and in poor soils. Lists of grasses for special sites are on pages 38–50.

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