Designing with Ornamental Grasses

Ornamental grasses provide two elements which can be difficult to create within a garden space – that being a dynamic sense of movement and eye-catching plant structure, which can be either horizontal or vertical in nature. They are also ideal for mass planting, using as bold solitary features or simply punctuating a mixed perennial border. There are both evergreen and herbaceous species available; meaning that there is a grass for every exposure or soil type, be it bog or dry as desert. If ornamental grasses as a whole have one downfall it is that there are so many of them that finding the right species for your landscape can be a bit mind-boggling; but I’m hoping to simplify this process with an overview of this important plant group.

Warm and Cool-Season Grasses

There are basically two classes of ornamental grasses based on their growing habits. Cool-season grasses typically enact growth in early spring and are in good form by late spring to early summer; a few of these include Calamagrostis ‘Karl Foerster’, Blue Oat Grass (Helictotrichon), Mexican Feather Grass (Stipa or Nassella) and Blue Fescue, all of which hold up well in the heat of summer. That said, a few cool-season grasses such as Bulbous Oat Grass (Arrhenatherum), Phalaris and Golden Millet (Milium effusum ‘Aureum’) might need to be cut back in the sweltering heat, as they can get quite unsightly but regrow with the cooler weather. Warm-season grasses such as Miscanthus, Pennisetum and Switch Grass (Panicum) are herbaceous in nature and require hot weather to enact growth – so these are in their prime from midsummer to frost. Divide or transplant them in late spring, while you can do the same to cool-season grasses from late winter to early spring. Evergreen grasses can be cleaned up in April by lightly pruning any winter-damaged tips or by running a gloved hand through the clump to remove any dead blades. Herbaceous grasses should be left for winter as many have dormant appeal and their seedheads feed a myriad of wild birds – these can be cut back hard in spring when the danger of frost has passed. Fertilizing is optional and in any case too much nitrogen will only result in floppy grasses and more work for you. So use a low rated 10-10-10 or 6-8-6 in early May or just lightly topdress with mushroom manure or compost without building it up on the crown.

Images in order: Blue Oat Grass with Coreopsis 'Zagreb', Mexican Feather Grass with Sedum 'Brilliant',

Runners vs Clumpers

Many new gardeners are under the impression that all ornamental grasses run or spread to some degree - but such is not the case. Take Carex for instance; while C. morrowii ‘Ice Dance’ is notorious for its spreading nature, Carex oshimensis ‘Evergold’ forms a perfect evergreen tuft of gold leaves with thin green margins. Included among the rampant spreaders are Variegated Reed Grass (Phalaris), Blue Dune Grass (Leymus arenarius) and Manna Grass (Glyceria maxima) – all of which have caught a few gardeners off-guard with their sprawling nature. But other spreaders such as Japanese Blood Grass (Imperata) expand so slowly that they are rarely considered invasive. The clumping species are many and include some of my favourites such as Fountain Grass (Pennisetum, especially ‘Karley Rose’), Japanese Silver Grass (Miscanthus sinensis) and of course Blue Fescue Grass (Festuca glauca). The other means of reproduction utilized by ornamental grasses is by self-seeding, which is more of a problem in warmer climes. However, many of the New Zealand sedges (Carex), Mexican Feather Grass (Stipa or Nassella) and Northern Sea Oats (Chasmanthium) have been known to self-seed locally.

Images in order: Japanese Blood Grass, Pennisetum 'Hameln', Rudbeckia 'Goldsturm' and Japanese Holly. Pennisetum 'Little Bunny' with Carex 'Evergold', Pennisetum 'Karley Rose'.  

Seasonal Planters

People often ask if some of the taller grasses can be accommodated in permanent mixed containers and as far as the long-term is concerned, the answer is no as they will quickly overwhelm adjacent plants. But that shouldn’t stop you from enjoying them in seasonal pots, with the added bonus being that you can combine them with whatever you want, since these are only temporary. Just have a permanent spot picked out in your garden for future placement after the container planting is past its peak. The fun part here is that everything is on the table including houseplants (bromeliads, Croton, Echeveria), flowering perennials (Liatris, Gloriosa Daisy, Delphinium), small shrubs (Skimmia, Lonicera ‘Baggesen’s Gold’) and even bedding such as Canna Lilies. This same approach can apply to alpine troughs; just plant them up with small 9cm grasses such as Carex ‘Evergold’ and a few evergreen perennials like Sedums, top dress with a little ornamental rock or sea glass and enjoy them until they outgrow the container. Then you just transplant them out in the garden and start all over again.

Planter 1 - Seasonal planter with Pennisetum 'Hameln', ornamental pepper, Euphorbia and sedum. Planter 2 - Seasonal planter with Northern Sea Oats, skimmia, heuchera, Gloriosa daisy and euphorbia. Planter 3 - Seasonal planter with Miscanthus 'Cosmopolitan', bromeliad, croton, delphinium, helenium and Gloriosa daisy. Planter 4 - Seasonal planter with Molinia 'Skyracer', canna lily, black-leaved dahlia, euphorbia, calceolaria, helenium and veronicastrum. Planter 5 - Seasonal planter with Miscanthus 'Strictus', liatris, sedum, hypericum, Pennisetum 'Karley Rose', echeveria, Shasta daisy and Angelica 'Vicar's Mead'.

Alpine trough with Carex 'Evergold', sedums and saxifraga.

Wet or Dry

Many ornamental grasses tolerate heavy, wet soils and a select few can even be used as submerged marginals in a pond or water bowl. For the latter choose any of the Papyrus (Cyperus), Fiber Optic Grass (Isolepsis cernua), Corkscrew Rush (Juncus effusus ‘Spiralis’) or the striking Bowles Golden Sedge (Carex elata ‘Aurea’). For planting in heavy clay soils try any of the Japanese Silver Grasses (Miscanthus sinensis), with some of my favourites cultivars being ‘Morning Light’ (white variegation) ‘Strictus’ (gold bands) and ‘Yaku Jima’ (dwarf). Calamagrostis ‘Karl Foerster’ also works well, as does Switch Grass or Panicum virgatum – with choice varieties being ‘Blood Brothers’ (wine highlights), ‘Heavy Metal’ (blue foliage) and ‘Shenandoah’ (red tips). Sandy soils or drought presents its own problems and while Blue Fescue Grass is often recommended for these growing conditions, it browns badly without adequate moisture. A few better choices include Blue Dune Grass (Leymus), Mexican Feather Grass, Big Bluestem (Andropogon gerardii) and of course Pampas Grass, which also comes with light pink plumes (‘Rosea’). If you are worried about the large size of the latter, you should be aware that many dwarf cultivars are now available including ‘Golden Goblin’, ‘Pumila’ and ‘Splendid Star’.

Images in order: Bowles Golden Sedge with Crocosmia 'George Davison', Joe-Pye Weed with Miscanthus 'Strictus', Waterbowl with Bowles Golden Sedge, Dwarf Papyrus and Spiral Rush, Pink Pampas Grass, & Miscanthus 'Yaku Jima'.

Made for the Shade

While a shaded garden does mean fewer ornamental grass options, you are not left without some attractive choices. The best place to start is with the Japanese Forest Grass or Hakonechloa macra. These herbaceous perennials have an elegant arching habit that presents well in a container or even when mass-planted in ground. The best cultivars to choose from include ‘Aureola’ (gold variegated), ‘Beni Kaze’ (purple highlights in fall), ‘Fubuki’ (white variegated) and the newer ‘Sunflare’ (gold with red tips). Next on my list of shade favourites is Lilyturf (Liriope muscari) which despite a strong resemblance is not a true grass, but it does provide a summer display of white, pale purple or violet-blue flower spikes. Liriope is reliably evergreen through winter with some of the better varieties being ‘Big Blue