Ornamental Grasses That Stay Put

Ornamental grasses have never been more popular… and for good reason. They have attractive summer foliage that dances in the wind and often persists, after changing color, through the autumn and even the winter. Plus many have feathery flowerheads that are just as long-lasting. They can be used in multiple fashions, from hedges or screens to filling hell strips to simply being dropped here and there in the perennial border. And there are grasses that are suitable for sun or shade, dry or wet soils, clay or sandy soils, cold or hot climates, etc. In fact, whatever your requirements, there is always a choice of ornamental grasses that will meet your needs!

Landscape architects and city planners have been at the forefront of the popularity of ornamental grasses. Many in fact include them in all their projects. Still, many home gardeners hesitate to try ornamental grasses. After all, aren’t they invasive?

The answer is yes… and no. Let me explain…

Three Categories

Ornamental grasses can be divided into three main categories, according to their root structure: three categories that also help determine their potential invasiveness.

The first is creeping grasses, the ones that produce long rhizomes and quickly form large colonies. Think of the common reed (Phragmites australis), a grass often seen in roadside ditches where, in certain cases, it has been known to spread for dozens of miles (kilometres), all from a single original rhizome.

All creeping grasses are considered at least somewhat invasive and some are so dominant that you shouldn’t even think of releasing them into a cultivated zone without surrounding them with an impenetrable barrier of some sort. (Try sinking a large pot or bucket with the bottom removed into the ground and planting the invader inside: that will keep it in check).

But there are also clumping grasses, that is to say, grasses that grow in dense tufts. They do expand in diameter over time, as does any perennial, but only very slowly. If they do get too big, all you have to do is divide them… again, just like any other perennial.

Finally, there is also an intermediate group: grasses with short rhizomes, sometimes called sod-forming grasses. They do expand outward, but don’t go very far, forming a tuft perhaps less dense that that of a clumping grass, but nothing truly invasive. Again, all you need is shovel to cut out any excess growth: that will put the plant back in its place.

How to Recognize an Invasive Grass

It is easy to distinguish between a potentially invasive grass and a clumping grass at the time of purchase. Just look in the pot. If the stems already form a dense clump, you’ll know it’s a clumping grass; if the stems are relatively close together, but without forming a real tuft, it’s a grass with short rhizomes; and if there are well separated individual stems that emerge here and there from the pot, it’s a creeping grass, likely to be at least a little invasive. Simple isn’t it?

Here are lists of popular ornamental grasses classified according to their growth habit.

Clumping Grasses

These grasses grow in clumps and are not invasive.

• Autumn moor grass (Sesleria autumnalis) zone 4
• Big bluestem (Andropogon gerardii) zone 3
• Blue fescue (Festuca glauca) zone 3
• Blue grama (Bouteloua gracilis) zone 3
• Blue hair grass (Koeleria glauca) zone 4
• Blue moor grass (Molinia caerulea) zone 4
• Blue oat grass (Helictorichon sempervirens) zone 4
• Bottlebrush grass (Hystrix patula, syn. Elymus patula) zone 4
• Bowles’ golden sedge (Carex elata ‘Aureus’, syn. ‘Bowles Golden’) zone 6
• Bunny tail (Lagurus ovatus) Annual
• Chinese miscanthus (Miscanthus sinensis) variable zone: 4, 5 or 6
• Common cottongrass (Eriophorum angustifolium) zone 1
• Common Rush (Juncus effusus) zone 4
• Diamond grass (Calamagrostis arundinacea, syn. C. brachytricha) zone 4
• Drooping sedge (Carex pendula) zone 5
• Elephant grass (Pennisetum purpureum) Zone 8
• Fountain grass (Pennisetum alopecuroides) zone 5b
• Foxtail barley (Hordeum jubatum) zone 3
• Frost grass (Spodiopogon sibiricus) zone 3
• Golden foxtail grass (Alopecurus pratensis ‘Aureovariegatus’) zone 2
• Gray’s sedge (Carex grayii) zone 2
• Great Basin wild rye (Elymus cinereus) zone 3
• Hardy clumping bamboo (Fargesia spp.) zone 4b
• Japanese sedge (Carex morrowii) zone 4
• Leather leaf sedge (Carex buchananii) zone 6
• Lesser quaking-grass (Briza minor) Annual
• Little bluestem (Schizachyrium scoparium) zone 3
• Mexican feather grass (Nasella tenuissima, syn. Stipa tenuissima) zone 6b
• Oshima sedge (Carex oshimensis ‘Evergold’) zone 6
• Pampas grass (Cortaderia selloana) zone 8
• Pink fountain grass (Pennisetum orientale) zone 6b
• Purple fountain grass (Pennisetum x advena ‘Rubrum’, syn. P. setaceum ‘Rubrum’) zone 8
• Purple Miscanthus (Miscanthus sinensis purpurascens) zone 4
• Quaking grass (Briza media) zone 4
• Ravennagrass (Saccharum ravennae, syn. Erianthus ravennae) zone 6
• Reed grass (Calamagrostis x acutiflora) zone 4
• Ruby grass (Melinus nerviglume, syn. Rhynchelytrum nerviglume) zone 9
• Seersucker sedge (Carex plantaginea) zone 3
• Sheep fescue (Festuca ovina) zone 4
• Snowy wood rush (Luzula nivea) zone 4
• Spiral rush (Juncus effusus ‘Spiralis’) zone 4
• Spring sedge (Carex caryophyllea) zone 5
• Tall moor grass (Molinia arundinacea, syn. Molinia caerulea arundinacea) zone 4
• Tufted fescue (Festuca amethystina) zone 4
• Tufted hair grass (Deschampsia caespitosa) zone 3
• Wood rush (Luzula sylvatica) zone 3

Grasses with Short Rhizomes

Yes, these grasses are creepers, but they only spread very slowly. They’re sometimes referred to as sod-forming grasses to distinguish them from the more invasive creeping grasses. They can easily they can be planted in a flowerbed without fear of them trying to take over.

• Blue sedge (Carex flacca) zone 4
• Bowles’ golden grass (Milium effusum ‘Aureum’) zone 5
• Broadleaf sedge (Carex siderosticha) zone 5
• Bulbous oat grass (Arrhenatherum bulbosum ‘Variegatus’) zone 4
• Coastal switch grass (Panicum amarum) zone 4
• Dwarf sweet flag (Acorus gramineus) zone 5
• Giant miscanthus (Miscanthus x giganteus, syn. M. floridulus) zone 4
• Gold-edged prairie cordgrass (Spartina pectinata ‘Aureomarginata’) zone 4
• Indian grass (Sorghastrum nutans) zone 3
• Japanese forest grass (Hakonechloa macra) zone 5
• Northern sea oats (Chasmanthium latifolium) zone 5b
• Palm sedge (Carex muskingumensis) zone 2
• Pennsylvania sedge (Carex pennsylvanica) zone 3
• Prairie dropseed (Sporobolus heterolepis) zone 3
• Side oats grama (Bouteloua curtipendula) zone 3
• Switchgrass (Panicum virgatum) zone 3

Grasses with Creeping Rhizomes

The following grasses may be beautiful, but they are highly invasive. In most cases, it’s best to plant these within a good root barrier.

• Amur silver-grass (Miscanthus sacchariflorus) zone 3
• Blue dune grass (Leymus arenaria ‘Glauca’) zone 4
• Bluejoint grass (Calamagrostis canadensis) zone 3
• Bullrush (Typha spp.) zone 3
• Bush grass (Calamagrostis epigejos) zone 3
• Common reed (Phragmites australis) zone 3
• Gardener’s garters (Phalaris arundinacea ‘Picta’) zone 3
• Giant cane (Arundo donax) zone 6
• Hardy creeping bamboo (Phyllostachys, Pleoblastus, Sasa, Pseudosasa, etc.) zones 5-10
• Japanese blood grass (Imperata cylindrica ‘Red Baron’) zone 5
• Skinner’s Gold Smooth Brome (Bromus inermus Skinner’s Gold ‘) zone 3
• Variegated manna grass (Glyceria maxima ‘Variegata’) zone 5
• Variegated orchardgrass (Dactylis glomerata ‘Variegata’) zone 5

Seedy Invaders

So much for grasses with invasive rhizomes, but some grasses are spread excessively through their seeds. The mother plant produces a huge number of seeds that sprout everywhere. This contrasts with the majority of grasses, which either only self-seed rarely or don’t do so at all. It’s worth dividing these plants into two groups, according to climate.

Grasses That Self-seed in Cold Climates

These grasses can be invasive due to their abundant self-sowing in cooler climates (zones 1-6). A good mulch will help keep them from spreading too abundantly.

• Blue hair grass (Koeleria glauca) zone 4
• Bowles’ golden grass (Milium effusum ‘Aureum’) zone 5
• Bullrush (Typha spp.) zone 3
• Foxtail barley (Hordeum jubatum) zone 3
• Gold-edged prairie cordgrass (Spartina pectinata ‘Aureomarginata’) zone 4
• Lesser quaking-grass (Briza minor) Annual
• Tufted hair grass (Deschampsia caespitosa) zone 3
• Wild Oats (Chasmanthium latifolium) zone 5b

Grasses That Self-seed in Mild Climates

The following grasses also can self-seed excessively, but only where the winters are mild (zones 7-12). There is no risk in the North, because either the grass is not cold hardy (several grasses, such as purple fountain grass, are grown as annuals in the North and don’t survive the winter there) or because, even if the grass is hardy, its seeds fail to ripen in the North (the case with most miscanthus grasses).

• Amur silver-grass (Miscanthus sacchariflorus) zone 3
• Bunny tail (Lagurus ovatus) Annual
• Chinese miscanthus (Miscanthus sinensis) variable zone: 4, 5 or 6
• Mexican feather grass (Nasella tenuissima, syn. Stipa tenuissima) zone 6b
• Pampas grass (Cortaderia selloana) zone 8
• Purple Miscanthus (Miscanthus sinensis purpurascens) zone 4
• Ruby grass (Melinus nerviglume, syn. Rhynchelytrum nerviglume) zone 9