July 2006

Miscanthus sinensis ‘Super Stripe’ By Paul Pilon

The popular Miscanthus sinensis is undoubtedly the most commonly produced ornamental grass. 'Super Stripe', also referred to as porcupine grass, is a great addition to this species and offers many improved attributes over other cultivars. Breeder and gardener Darrell Probst of Hubbardston, Mass., discovered this cultivar in a batch of seedlings in his garden. After years of screening, 'Super Stripe' was selected for its desirable characteristics including superior banding, sturdiness, early flowering and hardiness.

Being a warm-season grass, it does not begin to flush in the spring until temperatures are conducive for plant growth; usually 'Super Stripe' begins growing in late March or April. The foliage is variegated and consists of numerous golden bands. Its name, 'Super Stripe', accurately describes the amount of bands: This variety produces more stripes than other popular banded cultivars including 'Strictus' or 'Zebrinus'. The erect to slightly arching foliage reaches 4 ft. tall, with 7-ft.-tall flower spikes in the mid fall. The clumps reach 4 ft. wide after two or three growing seasons.

Porcupine grass is a clump-forming, warm-season grass and can be grown throughout USDA Hardiness Zones 5-9 and AHS Heat Zones 9-1. It is often used as a specimen plant or in mass plantings along highways or on golf courses. The foliage and flowers hold up rather well throughout the winter months, providing additional architectural interest during that time. 'Super Stripe' is easy to grow and always delivers an impressive display whether in bloom or not.

Propagation

Miscanthus 'Super Stripe' is vegetatively propagated by division. Division of porcupine grass is best when done in late winter or early spring while plants are still in a dormant state. It entails dividing or splitting the crown into smaller sections containing at least one stem, also commonly referred to as a culm or tiller, and several adjoining roots. Plant patent protection has been applied for, and self-propagation is strictly prohibited.

Production

'Super Stripe' is most commonly produced in 1-gal. or larger containers using 3-inch or larger-sized plugs obtained from a licensed propagator. Miscanthus will perform well in a wide range of growing mixes; using a media with adequate drainage and water-holding capacity is recommended. When transplanting plugs, try to avoid planting them too high or too low. Always plant to match the original soil line of the plug with the growing mix of the final container. This will keep plugs from drying out too quickly and discourage crown rot.

It is important to keep the root zones of newly potted grasses moist but not wet until they become established. Once fully rooted, miscanthus can be allowed to dry out more fully between waterings. Established containers require average amounts of irrigation and often need to be watered daily when they are actively growing. Plants can tolerate short periods of dry conditions, but perform best when an adequate amount of irrigation is provided.

'Super Stripe' is considered a moderate to heavy feeder. When applying constant liquid feed with water-soluble fertilizers, I recommend using rates of 100- to 200-ppm nitrogen with each irrigation. When fertilizer applications are applied weekly or as needed, higher rates of fertilizer, such as 300- to 400-ppm nitrogen, need to be used . Growers using controlled-release fertilizers should incorporate 1 1/4-1 1/2 lbs. of elemental nitrogen per yard of growing medium prior to planting or top dress the media surface using the medium or high rate recommended on the fertilizer label. The pH of the growing medium should be maintained within 6.0-6.5.

For plant establishment, maintaining average temperatures of 65-75¼ F is recommended. Produce miscanthus under high light levels with a minimum of 5,000 foot-candles. Plants grown under shade with consistently low light levels tend to be floppy and have lower-quality characteristics.

Several growers have expressed a need to reduce miscanthus' height when plants are grown in containers. Foliar applications are rather ineffective as the chemical has difficulty getting good contact with the stems, which are most often covered by the leaf sheath. When PGRs are applied as 1-time drenches, growers will commonly observe a reduction in plant height. The most effective PGRs are those taken up by the root system.

I recommend beginning with the following rates for each of the effective products: 10-ppm Topflor ( flurprimidol, SePRO), 10-ppm paclobutrazol (Bonzi, Syngenta Professional Products; Piccolo, Fine Agrochem-icals Limited; or Paczol, Chemtura Corp.) and 2-ppm Sumagic (uniconazole, Valent U.S.A. Corpora-tion). Since there has only been limited research using PGRs on grasses, it is best to conduct small trials before making wholesale applications over the entire crop. Drenches should be applied by the time the plants are 6-12 inches tall. Later applications seem to be less effective and will not provide desired results.

Porcupine grass is easy to overwinter when minimum amounts of protection are provided. In late fall after plants have gone dormant, trim them back to 2-3 inches above the top of the container. Once plants are trimmed, group pots together inside a coldframe, greenhouse or outdoor production bed. In many parts of the country, grouping plants together is the only protection necessary, especially if they are located in covered structures. In colder zones, I recommend covering plants with a protective frost blanket during the winter months. It is very important not to allow plants to dry out during the winter months; overly dry conditions during this time will usually result in crop losses.

Forcing

Most producers of ornamental grasses do not market them as flowering plants. In fact, unless they are produced and sold on site, it is often very expensive to ship tall flowering grasses to retail sites. When maintaining 65-75¼ F throughout crop production, 1-gal. pots of non-flowering miscanthus can be produced from large plugs in 7-9 weeks.

Porcupine grass has an obligate cold requirement for flowering. I recommend growers who wish to produce flowering miscanthus provide a minimum of 12 weeks of temperatures less than 40¡ F.

'Super Stripe' is an obligate long-day plant and will not flower when grown under short days. In fact, 'Super Stripe'will not grow and often goes dormant under short-day conditions. There has been relatively little research conducted to determine the exact forcing time for flowering miscanthus cultivars; I recommend producing them at 68-72¡ F for at least 16 weeks.

Pests And Diseases

Insects, including aphids, Japanese beetles, mealybugs, slugs and spider mites, may occasionally be observed feeding on plants but rarely become problematic. Control strategies may not be necessary unless scouting indicates a need.

Plant pathogens are also not very common when producing miscan-thus. Crown and root rots are the most common diseases observed. The onset of these diseases are often caused by improper planting practices, poor irrigation management, high salt levels in the growing medium or poor physical properties of the media (namely too much water-holding capacity and decreased aeration). Disease is also possible if the crop has been grown in the same container and growing mix for too long. Any of these conditions could lead to plant stress and the onset of root-rot pathogens.

Choose a growing mix that has good water-holding and drainage characteristics and will not deteriorate or settle over time. Monitor the irrigation practices and fertility levels on a regular basis, making adjustments accordingly. When possible, do not hold miscanthus in the same container for an extended period of time (12 months or more). When these measures are taken, most crown and root rots can be prevented.

Availability

Miscanthus 'Super Stripe' is marketed by Blooms of Bressingham (www.bobna.com). However, there is limited availability this year. Expect wider availability in the near future as more licensed propagators add this variety to their programs.