I was recently asked by my friend Mike Herr, aka “Mike the Mailman,” about dividing his ornamental grasses. And because I recently received a letter from my old friend and former colleague Dr. Gus van der Hoven, who is a retired professor from Kansas State University and owns 430 acres nestled in the beautiful Flint Hills outside of Manhattan, Kansas, I had prairie grasses on my mind. Mike’s question fit right in and gave me a lead in to how we can enjoy grasses in our own backyard and maybe create our own miniature prairie.
One thing I appreciate about grasses is they are adaptable and can grow in poorer soils better than many other garden plants. They also require little effort to maintain. They come in a wide variety of heights, colors and textures but do have varying water requirements. Ornamental grasses add two elements to the garden experience that are not readily obtained from many other plants: movement and sound.
Grasses add a significant vertical presence to the winter landscape and are commonly left standing until spring. Another benefit is that dried grasses have many decorative uses indoors and out. In the landscape grasses can be used as groundcovers, specimen plants, for erosion control and as vertical design elements.
The term ornamental grass includes not only true grasses (Gramineae) but also close relatives such as sedges (Cyperaceae), rushes (Juncaceae), hardy bamboos (particularly the genus Phyllostachys) and others. Some grasses grow best under warm temperatures and others in cooler temperatures.
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It is recommended to plant ornamental grasses in the spring. Container-grown grasses can be planted all season, stopping a month before first frost. Late planting of grass divisions is not recommended, particularly for warm season types. Grasses generally grow best in three to five hours of direct sun each day. In shade, these grasses may not bloom and tend to fall over, and may not develop peak fall color. Most grasses can benefit from mulching and many from cutting back, usually just before new growth begins in the spring. I would use hedge shears and wear gloves to prevent cuts from the razor-sharp edges of some species.
Ornamental grasses require relatively low levels of fertility. By keeping the level of nitrogen low, lodging or flopping over can be kept to a minimum. Leaf color and vigor are good guides to nitrogen requirements. Application of 1/2 to one pound of 10-10-10 fertilizers per 100 square feet of garden area or about 1/4 cup per plant is sufficient. Apply fertilizer just as growth resumes in the spring. An application of a slow release fertilizer such as Osmocote in the spring is enough to take care of the plant's needs throughout the summer. Fertilizer should be watered in thoroughly.
Plants should be well watered the first season after planting so they can develop a good root system. Established plants do not need regular watering, but may need supplemental watering during drought periods. The amount of water will depend on the grass species, the site, and on the quality, size and growth rate desired.
Cultivate around grass plants to control weeds. Application of mulch will greatly reduce the need for cultivation as well as watering. It also tends to keep grasses in check that have a tendency to be heavy reseeding types.
Grasses do not need to be cut down before winter. In fact, they are attractive when left standing and the foliage helps to insulate the crown of the plant. Cut back the foliage to about 4-6 inches in the spring before growth resumes. When foliage is removed, spring growth will begin earlier. Old foliage left on the plant can delay the crown’s warming and subsequent growth by as much as three weeks.
To answer Mike’s original question, a number of perennial grasses form dense root masses that can be very difficult to divide and transplant. A shovel or ax is recommended. Division depends on the spacing and visual appearance of the plants as well as the overall health. Plants suffering from die-out in the center should be divided to improve appearances. Division is done in the spring before growth resumes or in the late summer or fall after the growing season. Plants that bloom late could be divided in the spring. Most annual types can easily be grown from seed.
When I lived in Kansas back in late '80s and '90s and traveled up to speak in Iowa, I was in the tall grass prairie. The grass in this area can reach the height of a person or more. The soil is highly organic, the climate is more humid, and the soil moisture is more consistent. Dominant grasses include big bluestem (Andropogon gerardii), switch grass (Panicum virgatum) and Indian grass (Sorghastrum nutans).
West of Iowa in Kansas lays the transitional mixed grass prairie between tall and short grasses. Rainfall is reduced and the subsoil may be permanently dry, limiting grass height to 2 to 4 feet. Grasses in this area includes little bluestem (Schizachyrium scoparium), Western wheatgrass (Agropyron smithii), June grass (Koeleria macrantha syn. K. cristata) and needle grass (Stipa spartea). These grasses are mixed with species from the adjoining tall and short grass prairies depending on the soils, year and the rainfall.
I always enjoyed sitting on the prairie while hunting deer, as the sun was setting behind me and watching the sun reflecting off the grasses. It gave a beautiful reddish hue to the prairie landscape. Enjoy the beauty of ornamental grasses and create your own prairie in Pennsylvania.