Leaf through any glossy gardening magazine and chances are you will come upon several pages of stylized perennial garden sketches, one for shade, one for full sun, one to attract bees, another to draw butterflies. But do any of those slick garden designs ever include ornamental grasses? Hardly ever. That’s a pity. A garden that mixes ornamental grasses with flowering perennials adds new textures, adds motion, and adds months to the life of the garden long after all those flashy perennials have dropped dead.
Ornamental grasses fall into one of two groups, those that like it cool and wet and those that like it hot and drier. A cool season grass begins growing at the end of winter, putting on its finest show in early spring but going dormant in summer, even browning out and dying back. A warm season grass is slow to show its face in spring but comes into its glory in the heat of summer. This distinction is important when planning your ornamental grass garden. Plant only cool season grasses and you’ll have empty patches of dirt in summer. Plant only warm season grasses and you’ll have empty patches of dirt all spring. Balance is the key – plant some of both for a continuous display through most of the year.
Apart from their growing patterns, cool season and warm season grasses have differing needs. Cool season grasses need plenty of moisture, loving April showers, and require frequent dividing, say every second year, to avoid the “donut hole” look, brown in the center with a ring of new growth around the outside. Warm season grasses generally don’t need as much water or division, but they are slower to get established than their cool season buddies; they should be planted in late spring so they have a chance to put down strong roots before the onslaught of winter.
A cool season grass that does not suffer from the ‘donut hole’ syndrome, Hakonechloa macra, Japanese Forest Grass, is one of the only grasses to thrive in full shade. Named for Mt. Hakone in Japan, this lover of woodland conditions puts out yellow-green flowers above its bamboo-like foliage in mid-summer but dies to the ground in winter. Although it spreads by rhizomes this handsome foot tall specimen (hardy to USDA Zones 5-9) is well mannered, never running amok. Two stunning cultivars are ‘Aureola’ which has a gold stripe running down its green blades
and ‘All Gold’ with bright yellow foliage.
Two other cool season grasses that love moist conditions are Purple Moor Grass and Feather Reed Grass. Purple Moor Grass or Molinia caerulea,
gets its common name from the moors of Europe where it was first spotted and the purple tint of its airy seed heads that emerge in early July. Favoring full sun and acidic soil, this fountain shaped grass stands about 2 feet tall and is hardy to USDA Zones 4 – 9. To set your garden aglow plant it in a spot where its silvery green foliage and plumes are backlit by the early morning or late afternoon sun. The other cool season selection that thrives in wet soil Calamagrostis x acutiflora or Feather Reed Grass is often used to anchor stream banks. This tidy compact grass sports green blades about 3 feet tall and fluffy sandy fronds in June that look like sheaves of wheat. Named Perennial Plant of the Year in 2001 by the Perennial Plant Association, Calamagrostis (USDA Zones 3-9) wants full sun and will tolerate heavy clay soils. A cultivar of note is ‘Karl Foerster”named for a German nurseryman who introduced this grass to the world in 1950.
Rounding out the discussion of cool season grasses, two that prefer dry soil are Blue Oat Grass, Helictotrichon sempervirens,
and Blue Fescue, Festuca glauca, both very similar in appearance although Blue Fescue is barely a foot tall whereas Blue Oat Grass is double the height. These two blues have similar foliage, spiky thin blades forming a porcupine-like clump, and both are semi-evergreen. Blue Oat Grass (USDA Zones 4-9) blooms earlier than Blue Fescue (USDA Zones 4-8) putting out airy beige flower clusters in early June that last well into fall, and for the best steel blue color plant it in a sunny dry spot. The Royal Horticultural Society recognized the value of Helictotrichon by honoring it with the coveted Award of Merit in 1993. If a 2 foot tall grass that grows 3 feet in diameter is too grand for your site, choose Festuca glauca a daintier version that is equally at home in a rock garden or in the front of a perennial border. The variety ‘Elijah Blue’,
introduced by The Plantage Nursery on Long Island, is readily available at nurseries and garden centers. This dwarf, blooming in early summer, should be divided every 2 – 3 years to avoid the ‘donut hole’ look.
Turning attention to the warm season grasses, three selections that can tolerate moist soil are Panicum virgatum, Pennisetum alopecuroides, and Chasmanthium latifolium. Dismounting from the botanical high horse, they are commonly known as Switch Grass, Fountain Grass, and Indian Woodoats. Beginning the discussion, Panicum virgatum or Switch Grass (USDA Zones 5-9) is a tough prairie native that produces an airy cloud of pink plumes from July through February – now that’s longevity for you. For an “Oh, wow!” garden moment choose the stately cultivar ‘Heavy Metal’ whose blades mature to a metallic blue forming a dramatic backdrop for the pink cloud of flowers.
Preferring full sun it can stand a little shade, but do keep the soil lean; too much fertilizer will cause it to flop over. Fountain Grass or Pennisetum alopecuroides
also blooms from July to February, its bottle brush flowers rising above a fountain of green change from whitish purple to copper purple as the days grow shorter. Again, as with many of the ornamental grasses, give it as much sun as possible for the best color. Fountain Grass (USDA Zones 5-9) is known to be invasive in some states, and if this is a concern, simply remove the seed heads to prevent its spread. The final selection for a warm season grass that likes moist soil is another mid-Western native Chasmanthium latifolium or Indian Woodoats (USDA Zones 4-8),
one of the more shade tolerant ornamental grasses. Shaped like Indian arrowheads the seed heads emerge in August changing from green to bronze as the summer wanes, and when stirred by a breeze they make a calming rustling sound. Often used to hold stream banks in place because of its affinity for wet soil, this toughie also can take wind and salt spray a real plus for those who garden at the coast.
Two ornamental grass selections that prefer dry conditions are Miscanthus sinensis and Schizachyrium scoparium or more familiarly Little Bluestem. Introduced in the late 1800’s Miscanthus sinensis
or Chinese Plume Grass needs full sun to remain its upright regal self, but it can tolerate drought and air pollution making it a favorite of urban gardeners in USDA Zones 5-9. The cultivar ‘Gracimillimus’ bursts forth in August with 6 foot pink plumes that will hang on through the winter if you hold off whacking it back until spring. For those in the more temperate climates who fear its invasive nature, applying a heavy layer of mulch will curb the spread of the seeds. Little Bluestem, native to the prairies of North America,
is half the size of Miscanthus but shares many of the same traits; it too produces pink plumes from August to February, and also can withstand drought and air pollution. But unlike Miscanthus Little Bluestem is celebrated for its dramatic fall show when its blue-green blades change to a brilliant bronze-orange.
Finally, most discussions of ornamental grasses generally include two grass lookalikes, Carex pensylvanica and Sisrinchium angustifolium. Carex pensylvanica
is really a sedge, a marsh plant, not a grass at all (hardy in USDA Zones 3-8), and for those who prefer native plants, a Carex is a good substitute for Hakonechloa, thriving in part to full shade. Another native of North America Sisrinchium angustifolium, or Blue-eyed Grass (USDA Zones 4-9),
is a member of the Iris family, and at a dainty 1½ feet it is an ideal choice for a sunny rock garden. Its ribbon-like leaves resemble a grass, but in the spring this little beauty puts out delicate blue flowers surrounding a yellow eye that never fail to induce a smile.
So when planning your perennial garden flip past those sketches in that glossy magazine and create a design that includes choices from the vast and varied world of ornamental grasses, and you will add another dimension to your garden, one that introduces movement, texture and structure.
Digging Dog Nursery
High Country Gardens
Hakonechloa macra ‘All Gold’ – The Designing Gardener
Molinia caerulea – Elke Freese
Calamagrostis x acutiflora ‘Karl Foerster’ – The Designing Gardener
Helictotrichon sempervirens – Sten Porse
Festuca glauca ‘Elijah Blue’ – The Designing Gardener
Panicum virgatum ‘Heavy Metal’ – The Designing Gardener
Pennisetum alopecuroides – Daderot
Chasmanthium latifolium – Eric in SF
Miscanthus sinensis – Miya.m
Schizachyrium scoparium – Montrealais
Carex pensylvania – Chhe
Sisrinchium angustifolium – Meneerke bloem