New Ornamental Grasses at the Iowa Arboretum

Ornamental Grasses at the Iowa ArboretumSince 1995 when the Ames Garden Club funded a trial bed of 25 cultivars ofMiscanthus sinensis, Japanese silver banner grass, the Iowa Arboretum hasbecome known for its ornamental grasses. With the addition of a second grassborder in the perennial garden area in 2008 we now display 66 ornamental nativeand exotic grasses -- certainly one of the most varied assemblages in Iowa.We’d like to share what worked and what didn’t with our readers and potentialvisitors.Iowa is the land of the tall grass prairie with soil and sunshine ideal for the growthof many members of the grass (Poacae) family. Grass-like plants such assedges (Carex species) and rushes (Juncus species) can also grow well, albeit inmore shaded or moist locations. Our major challenge is winter hardiness – somebeauties such as Pampas grass (Cortaderia) and purple fountain grasses(Pennisetum) -- can only be grown as annuals. The Arboretum often behaveslike a pocket of USDA Hardiness Zone 4 in the midst of a Zone 5 area, so wetake some risks in incorporating Zone 5 rated plants. However, you can be fairlyconfident that what survives here will grow in your garden even in the far reachesof Iowa.Why Grasses? Grasses provide contrasting texture to broad-leaved plants andthe element of movement in the garden. Taller ones add height and screening toa border and offer a green background against which to display colorfulperennials. Low maintenance attributes include few pests and diseases and noneed for additional fertilizer. Too many nutrients can cause them to flop. Afterestablishment, these are also water-wise plants, requiring no irrigation.With careful choices, grasses can provide almost year-round interest. Along withconifers, grasses prevent your garden from becoming a “dead zone” punctuatedby plant markers throughout long winters. Many bloom late in the summer orearly fall and their blossoms (inflorescences) and foliage remain attractive overthe winter. Miscanthus sinensis and switchgrass (Panicum virgatum) cultivars aresome of the best choices for winter interest as their foliage and blooms hold well.Those with more slender foliage or earlier bloom such as the very popularFeather Reed Grass (Calamagrostis ‘Karl Foerster’) and Purple Moor Grass(Molinia caerulea) generally look ragged by spring.Seasonal Care: The main chore is cutting back foliage once a year. CutMiscanthus and most other grasses down to a short stubble (3-4 inches) in lateMarch or early April. If you have a lot of grasses, use a brush cutter or hedgetrimmer and be prepared to dispose of a “haystack”. Cool season grasses,notably Calamagrostis, start growing in March so consider cutting them back inthe fall if you typically get a late start on spring work. By June Calamagrostis hasgrown to its full foliage height and soon the tawny seed heads provide a newsummer show. Other grasses such as Fescues, Sedges, and Blue Oat Grass

(Helictotrichon) are almost evergreen. Use your gloved hands to pull out the oldgrowth rather than shearing them off.Miscanthus sinensis Cultivars: Breeders have given us over 100 cultivars fromwhich to choose. The largest we display is the aptly named ‘Silberfeder’, makinga 7-foot wide fountain with feathery, silvery flowers; the smallest is ‘Gold Bar’ atabout 18 inches with a strictly upright physique. The fine textured, late floweringolder cultivar ‘Gracillimus’ or Maiden Grass holds well over winter but an earlyfrost can doom its blossoms, robbing the winter show. Earlier flowering cultivarssuch as ‘Bitsy Ben’ and ‘Nippon’ look handsome in late summer but don’t alwayshold over winter. We’ve also observed seedlings (undesirable) near some ofthese.A few Miscanthus cultivars have fine textured foliage: examples in our collectioninclude ‘Sarabande’, ‘Gracillimus’, its variegated sport ‘Morning Light’, ‘Graziella’and ‘November Sunset’. Most have wider blades. Form can be very upright as in‘Strictus’, ‘Gold Bar’, and purpurescens (Flame Grass) or fountain-like as in‘Silberfeder’ (wider than tall) with most cultivars falling between these extremes.There are many variegated forms, both green/white and green/yellow. Verticalstripes are found on ‘Morning Light’, ‘Rigoletto’, and ‘Variegatus’. Horizontal goldbars decorate ‘Strictus’ (Porcupine grass), ‘Zebrinus’ (not on display – not hardyfor us), ‘Kirk Alexander’, ‘Gold Bar’, and ‘Puenktchen’. Variegated foliage,particularly on wide-bladed cultivars, makes the grass clump stand out in yourgarden even when not in bloom.A border of other grasses: Both exotic and native grasses were used in a 2008naturalistic planting designed by Ann Hutchins of Des Moines. You could call it a"no Miscanthus border" although a spectacular new variegated Miscanthuscultivar, 'Gilded Tower', was allowed to sneak in. The bed was bermed andprovided with a good cover of pine bark mulch. Several varieties of fescues,variegated feather reed grasses, switchgrasses, fountain grasses, sedges,gramas, Indian grasses, and moor grasses were selected. My personal favoritesamong these new grasses, also admired by our visitors, are featured below.To better display grasses as they might be used in a home garden, we choseaccompaniments from among the sophisticated new cultivars of coneflowers(Echinacea), false indigo (Baptisia), asters (Aster), blanket flowers (Gaillardia),coreopsis (Coreopsis), salvias (Salvia), catmints (Nepeta), bee balms (Monarda),goldenrods (Solidago), sunflowers (Heliopsis), and black-eyed susans(Rudbeckia). These are all low-maintenance plants that blend well with grasses.I especially like Coreopsis 'Jethro Tull', several Echinacea cultivars of the ‘BigSky’ series, and Gaillardia ‘Amber Wheels’.What didn’t work? Dwarf or variegated varieties are often less hardy than thespecies. We’ve lost M. sinensis ‘Zebrinus’ and ‘Morning Light’, Purple Three-Awn (Aristata purpurea), Northern Pampas Grass (Saccharum ravennae), and

Pennisetum cultivars ‘Foxtrot’, ‘Karley Rose’, ‘Little Bunny’ and even some of thestraight species alopecuroides. However ‘Morning Light’ thrives next to theHughes Education Center and Saccharum ravennae overwintered in my Amesgarden.The Iowa Arboretum was "ahead of the curve" in featuring ornamental grassesfifteen years ago. The new border showcases some lesser known species andnew releases for your consideration. The complete listing of the Arboretum’sornamental grasses is found on our web site (www.iowaarboretum.org). We hopeyou’ll visit both the grounds and the web site to select grasses for your owngarden.