ornamental grasses add beauty and interest to the garden. Their dramatic change through the seasons gives a new dimension to the garden: an informal, natural look that is unique and refreshing. The objective of this bulletin is to publish the field research results from many grasses grown at four locations over 17 years in Minnesota. Information is included on culture, landscape features, and special uses of these grasses. This information should be useful to gardeners, nurseries, garden centers, landscape designers, and home-owners who live and garden in cold climates of the United States.

Winter survival or hardiness information is
based on research at the University of Minnesota, including multiple growing locations in USDA Zones 3 and 4. Illustration 1 (on page 4) shows the growing sites and years of field research. The grasses listed in this publication are hardy in USDA Zone 4, unless otherwise indicated. Plants that survived in USDA Zone 3 are listed on page 29. Although the research was conducted in Minnesota, this information is applicable to many states with similar climates from Maine to Montana.

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 further apart for specimen plants, or space plants one-half their height for a hedge or screen.

Division (digging 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 restoration or for planting large areas where diversity is desirable.

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

Cut back ornamental grasses to the ground to remove the previous year's growth. This should be done each year in late winter or early spring, before new growth starts. If the plants are not cut back, spring growth will be delayed and large plants will look unattractive and 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. In this study, the grasses were burned to the ground, usually in early April. Some cool season grasses may be semi-evergreen such as Deschampsia, Festuca, and Helictotrichon and should be carefully cut back or any dead foliage and flowers removed with a rake or by hand. Burning cool season grasses should only be done when the plants are all brown and dormant. Do not cut back
or burn any grasses in the fall as winter injury may result and the winter beauty of the plants is lost.

In these field research plots, the soil pH varied from 7.2 to 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 to 8.0. Established grasses rarely need fertilization or irrigation except in cases of extreme drought or very sandy soils. In this research, organic wood chips were applied annually to prevent weeds.

Hand weeding, or spot treatment with a contact herbicide for persistent weeds such as quackgrass was done in this study to eliminate weeds. Rust was occasionally noted on some species 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, but no damage was noted.