The popularity of ornamental grasses has soared in recent years. In the garden, they can be bold, natural, textural and graceful — truly adding a “new” look to mixed containers, gardens and landscapes. In ever increasing numbers, they are being produced and sold with annuals and perennials. Many bedding plant growers would like to enter the market but are often unfamiliar with the plant material and have limited access to published information. We are getting more requests for information on selection, propagation, production and especially timing so growers can efficiently enter this rapidly expanding market. Growers are interested in learning more about small grasses that will work well in containers or even with bedding plants. At the same time, they are attracted to larger grasses and have requested more information on those with excellent ornamental characters combined with good garden performance. The fact is that production research efforts on ornamental grasses have been few, and published information is limited.
At Michigan State University, we have trialed landscape performance of ornamental grasses for over 20 years. We now have several gardens that focus specifically on ornamental grasses. The popularity of these gardens and associated programs attests to the increased awareness by gardeners of all experiences. We currently are testing about 100 selections for hardiness in Zone 5. For information on Zone 4 hardiness, growers should look to the trials in Minnesota conducted by Mary Hockenberry Meyer, who has had a long-term interest in ornamental grass performance in Northern climates. Trials in Michigan and Minnesota include small and large ornamental grasses, though traditionally, the focus has been more on landscape performance. In the past couple of years, we initiated a research program to investigate selection, propagation, production and scheduling of ornamental grasses for greenhouse growers. Our objectives are to develop innovative propagation techniques, particularly cutting propagation, determine photoperiod and vernalization requirements and develop greenhouse production schedules for a wide range of ornamental grasses and grass-like plants.
Short grasses, tender and hardy, are rapidly becoming important greenhouse crops. There are numerous short grasses worthy of production, and many are perhaps best suited for use in containers. They readily add texture and interest to containers. In Figure 1, left, some of the more popular short grasses are listed with short descriptions on performance. Some are hardy to Zone 3; some are tender; and a few are true annuals. Several, such as juncus, are not true grasses but are often lumped with grasses based on texture and form. Others, such as Hordeum jubatum (foxtail grass) and Imperata cylindrica (blood grass), can be very ornamental but are considered pests in certain parts of the country.
Purple fountain grass (Pennisetum setaceum ‘Rubrum’) is a tender perennial that has taken the Northern states by storm the past several years. In fact, purple fountain grass was hardly grown in Northern states until a few years ago. Now, Michigan growers alone produce hundreds of thousands in containers each Á year. Purple fountain grass is sterile and must be produced vegetatively, often by divisions. There are issues relative to stock plant management, chilling injury and inadequate red in low light conditions. Still, the fantastic ornamental display combines well for container use and in the landscape.
Some valuable short grasses, such as Hakonochloa macra, have a reputation for being difficult and slow to grow. We have found that Hakonochloa grows best under long-day photoperiods without an exposure to cold. The key appears to be constant photoperiod and temperature control (see Figure 3, right). Even from a small division, a reasonable plant can be produced in six weeks.
There is no doubt that I personally like grasses big, bold and beautiful. This includes many selections of miscanthus, Panicum virgatum (switch grass), Pennisetum alopecuroides (fountain grass) and the popular calamagrostis ‘Karl Foerster’. However, despite their showy appearances in the garden, these same grasses typically look poor in containers. Little is known about techniques for optimizing starting material and subsequent flowering requirements. Almost all of the superior ornamental grasses are propagated vegetatively — a relatively slow and cumbersome process. Crown division, the principle method of multiplication, is labor intensive and must be properly timed for best results. Large amounts of space and labor must be devoted to stock plants, which should be dug and divided each season for best results. Cutting propagation of some grasses such as purple fountain grass has been demonstrated, though few growers have adopted this technique due to inconsistent results during commercial implementation.
We have begun initial screening for growth and developmental responses to photoperiod and cold and light quantity, and we have preliminary data for about 20 ornamental grasses. All ornamental grasses tested, including Miscanthus sinensis, Panicum virgatum, helictotrichon and Pennisetum alopecuroides flowered only under long days. While most selections appeared to have an obligate cold requirement, there were some Á notable exceptions, including Panicum virgatum and Hakonochloa macra. While this data provides a useful foundation, there are still many questions that remain unanswered before it can be utilized to construct more efficient production protocols. These are issues that we hope to address in our research efforts in the next several years.
It seems that American gardeners are more knowledgeable than ever, and with this knowledge comes an ever-increasing appetite for new plant material. Ornamental grasses offer a new look and in turn a great opportunity for gardeners of all experiences — novices and pros alike. The smaller grasses can look great in containers and can often sell themselves when grown well. The larger grasses are proven performers in the landscape and are in great demand. Still, we have a long way to go to streamline propagation and optimize production techniques. I have few doubts that we will see many changes in the future in the way these plants are produced and marketed. As an ornamental grass enthusiast, I look forward to seeing even more of these great plants in the landscape.
Michigan State University trials determine which ornamental grasses make the grade.