Helictotrichon sempervirens (Blue Oat Grass) – A cool season evergreen clump-forming grass that grows to 2 feet tall by up to 3 feet wide with blue-gray leaves radiating out like a bristly porcupine. The light tan flowers are on erect spikes that rise a foot above the foliage in mid-summer, though flowering is not as strong or commonly seen in southern California as in areas with cooler winters. Plant in full sun or light shade and give occasional irrigation. This plant remains evergreen in mild climates but is considered semi-evergreen in areas that experience harsher winters and is hardy to USDA zone 4 and perhaps 3. In these areas it is best to trim plants back close to the ground in late winter. It performs best in soils with good drainage and may rot in heavy soils, especially if over irrigated. The blue color seems best in dryer soils when plant is in full sun or bright shade; too much shade and the plant flops over and opens up in the middle. Maintain plants by removing withered leaves as they appear or by occasionally pulling a steel rake through the foliage. This stunning European grass has long been one of the most popular grasses we have grown, but observations over time of plantings of it have us questioning its suitability as sustainable plant in our mediterranean climate, particularly in warmer southern California where it tends to last only a few years but does seem to perform better in cooler northern California. It is native to central and southwestern Europe (France to Italy) and, where it is happy, it is a great grass for use as an accent plant or in mass plantings. The genus name Helictotrichon comes from the Greek words ‘helictos’ meaning “twisted” or “spiral” and ‘trichos’ meaning “hair” or “spine” in reference to the twisted awns with the specific epithet meaning evergreen. Helictotrichon sempervirens won the coveted Award of Garden Merit from the Royal Horticultural Society in 1993. The information on this page is based on research conducted in our nursery library and from online sources as well as from observations made of this plant as it grows in our nursery, in the nursery’s garden and in other gardens that we have observed it in. We also will incorporate comments received from others and always appreciate getting feedback of any kind from those who have additional information, particularly if this information is contrary to what we have written or includes additional cultural tips that might aid others in growing Helictotrichon sempervirens.

Helictrotrichon at the Denver Botanical Gardens.

Blue oat grass, Helictotrichon sempervirens, is a cool season, clump-forming grass with steel-blue foliage. This is an award-winning plant for any garden. It won the Award of Garden Merit from the Royal Horticultural Society in 1993 and was selected for Great Plant Picks in 2004. The neat, bristly mounds make an attractive ornamental plant. It is similar in appearance to blue fescue (Festuca ovina glauca cultivars), but taller and with sturdier blades.

Blue oat grass forms nice clumps of steely blue foliage.

Native to central and southwestern Europe, this perennial grass is hardy in zones 3 or 4-8.The long, wiry leaves on arching stems are about ½ inch wide and taper to a fine point. Under optimal conditions it grows about two feet tall and three feet wide. Graceful flower plumes grow vertically from the center of the plant. Pale blue flowers bloom on beige, one-sided panicles in midsummer. It often does not consistently produce the attractive, arching four foot flower stems in more northern areas where there is a shorter, cooler growing season. The leaves turn light brown in autumn and persist through the winter.

Helictrotrichon combines well with other grasses and perennials.

This small ornamental grass has many landscape uses, with a color and texture few plants have. It makes a nice addition to the perennial border, particularly as a contrast to green-leaved plants. Use it as a single accent plant in the smaller garden or rock garden, grow it in masses for a fine-textured drift, or try it in a container. Blue oat grass makes a nice row along a walkway, or can be added to the front of a shrub border. It combines well with Russian sage (Perovskia), Salvia x sylvestris ‘Mainacht’ (‘May Night’), blanketflower (Gaillardia), Sedum ‘Autumn Joy’ and other, more upright ornamental grasses. Use it to echo the blue foliage or flowers of blue spruce, blue junipers or blue-flowering perennials such as Campanula, lavender (Lavendula), or blue mist spirea (Caryopteris). For a more dramatic effect, try combining it with plants with deep maroon leaves.

Blue oat grass produces tall flower spikes above the leaves.

Plant blue oat grass in full sun. Well-drained soil is essential for winter survival. Although it prefers a moist soil, it will tolerate sandy as well as heavy clay soils – as long as it does not remain too wet in winter. Evergreen in milder climates, the leaves die back in Wisconsin winters; use a rake to remove the old foliage or cut back close to the ground in late winter. This plant has no significant insect pests or diseases other than crown rot that occurs in poorly drained soils.

There are a few cultivars:

  • ‘Sapphire’ has finer blades that are slightly smaller and bluer than the type.
  • ‘Saphirspudel’ (‘Sapphire Fountain’) is a finely textured, semi-evergreen selection from Germany.

Propagate blue oat grass by division in the spring or grow from seed. Sow fresh seed in late summer, keep over the winter in a cold frame, and they should germinate in spring.

– Susan Mahr, University of Wisconsin – Madison


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Blue Oat Grass in bloom

Blue Oat Grass in bloom

(Photo courtesy of NetPS Plant Finder)

Blue Oat Grass

Blue Oat Grass

(Photo courtesy of NetPS Plant Finder)

Plant Height: 24 inches

Flower Height: 3 feet

Spread: 24 inches

Sunlight:

Hardiness Zone: 3a

Ornamental Features

Blue Oat Grass’ attractive grassy leaves remain steel blue in colour throughout the year. The tan seed heads are carried on plumes from mid summer to late fall. The flowers are not ornamentally significant.

Landscape Attributes

Blue Oat Grass is an herbaceous evergreen perennial grass with a mounded form. It brings an extremely fine and delicate texture to the garden composition and should be used to full effect.

This is a relatively low maintenance plant, and is best cut back to the ground in late winter before active growth resumes. It has no significant negative characteristics.

Blue Oat Grass is recommended for the following landscape applications;

  • Border Edging
  • General Garden Use

Planting & Growing

Blue Oat Grass will grow to be about 24 inches tall at maturity extending to 3 feet tall with the flowers, with a spread of 24 inches. Its foliage tends to remain dense right to the ground, not requiring facer plants in front. It grows at a medium rate, and under ideal conditions can be expected to live for approximately 10 years.

This plant should only be grown in full sunlight. It prefers to grow in average to dry locations, and dislikes excessive moisture. It is not particular as to soil type, but has a definite preference for alkaline soils, and is able to handle environmental salt. It is highly tolerant of urban pollution and will even thrive in inner city environments. This species is native to parts of North America. It can be propagated by division.

Ornamental Oat Grass – How To Grow Blue Oat Grass

Grasses add drama to the garden and accentuate and complement other garden specimens. If you are looking for an attractive ornamental grass with a unique color, look no farther than ornamental blue oat grass. Read on to see how to grow this blue hued ornamental oat grass variety.

What is Blue Oat Grass?

Native to Europe, ornamental blue oat grass (Avena sempervirens syn. Helictotrichon sempervirens) is a perennial grass with a dense, clumping habit of foot long stiff, blue green foliage about ½ inch wide and tapering down to a point. Blue oat grass resembles blue fescue although it is larger; the plant grows 18-30 inches tall.

Flowers are borne from the tips of the tapered leaves tipped with golden oat-like seed heads. Beige panicles are produced June through August, eventually achieving a light brown hue by fall. Blue oat grass maintains its attractive light brown fall color through the winter.

Blue oat grass is good as an accent plant of in

mass plantings. The blue/green foliage with a silvery cast is an excellent eye catcher and accents the green foliage of other plants.

How to Grow Blue Oat Grass

Ornamental blue oat grass is cool season grass. United States Department of Agriculture zones 4-9 are suitable for growing ornamental blue oat grass. The grass likes moist, well-drained soil in full to part shade. It prefers fertile soils but will tolerate less fertile as well as sandy and heavy clay soil. Plants are usually set two feet apart to form a solid mass of foliage.

Additional plants can be propagated by division in the spring or fall. Blue oat grass does not spread via rhizomes or stolons like other grasses so it is a less invasive option for the landscape. New seedlings will pop up of their own accord, however, and can be removed or moved to another area of the garden.

Blue Oat Grass Care

Blue oat grass care is minimal, as it is a forgiving and hearty grass. Heavy shade and little air circulation foster foliar disease on blue oat grass but, otherwise, the plant has few problems. It does tend to get rusty looking, especially when it is overly humid and wet, usually if it is in a shaded area.

No more than yearly feeding is needed to keep the plants thriving and they should last for years with very little care.

Growing blue oat grass can be pruned back in the fall to remove old leaves or at any time they are looking a bit peaked and need some rejuvenation.

Of ornamental oat grass varieties, A. sempervirens is the most common, but another cultivar ‘Sapphire’ or ‘Saphirsprudel’ has an even more pronounced blue hue and is more rust resistant than A. sempervirens.

When it comes to pruning ornamental grasses, even an ordinarily confident gardener can feel some confusion. Each type of grass has different requirements, which makes it hard because there’s not one rule of thumb which fits all. While some varieties look shaggy and sad if not whacked to the ground each January, for other types of grass this treatment sounds the death knell.

Not to worry. I’ve got you covered with a list of the ornamental grass varieties that are grown most commonly, and simple instructions for how to prune each. Though I live in the coastal Pacific Northwest and have geared my instructions towards people in similarly rainy climes, the only thing that would be different in a climate where it snows is that you would have to prune your grasses either earlier before the first snow, or later in midspring.

In cold climates, I’d advise pruning grasses as late as possible, since snow-covered ornamental grasses make a sculptural display in the landscape, and by allowing the seeds to sit on the plant, you provide birds with an important food source through a tough time of the year.

Ready to prune your grasses?

For ease of reference, I’ll start with the largest varieties and work my way down to the smallest.

Flax (Phormium) and clumping varieties of festival grass (Cordyline). This is one of the toughest plants for people to wrap their minds around pruning, because their bold colors and spiky nature make them an instant focal point in the garden. So the penalty for doing it wrong is staring at a very ugly plant for some time. Luckily, pruning these plants isn’t difficult, just a little time-consuming.

You can approach them in one of two ways. Keep them looking nice by using your hand pruners to individually remove any blades that are brown, have been damaged by snails, or are old and have lost the vibrant color of their new growth (on flax). Simply put on some eye protection, then cut each blade as far down into the base of the plant as possible. You can also control size in this way, by spending a peaceful half hour removing the tallest blades one at the time.

The second method is to ignore them until they are unattractive and oversized, and every few years whack them to the ground. Once they come back, you’ll have a honeymoon period of about six months when they look flawless and colorful again, and then you will start wishing you had the patience to cut out the unattractive individual stalks to keep them looking nice.

Cape rush (Chondropetalum), Papyrus (Papyrus) and rush (Juncus). Restios and rushes are gorgeous in the landscape because they have an upright habit and deep green foliage which looks good year-round. However, it’s best to put them in a location where they are going to be happy and will have room to spread out, because they resent being pruned and can take over a year to even begin to look okay again after being attacked by the hedger. If there is a buildup of brown strands, cut them out individually as low to the ground as you possibly can. A healthy plant should have very few leaves that aren’t green.

Maiden grass (Miscanthus), feather reed grass (Calamagrostis), Giant pheasant’s tail grass (Stipa gigantea). Maiden grass and ot her large grasses that go fully dormant actually benefit from and appreciate being pruned down to about 10 inches tall each January. Start by putting on some gloves and long sleeves to prevent cuts, then tie the grass into a bundle with a spare bit of rope, lay a tarp next to the plant, and use your powered or handheld hedging shears to give them a quick buzz cut.

The one thing you should never do is prune off just the tops and flowers in fall, as I see so many overzealous lawn care companies do. That takes away the loose, airy beauty of the fall and winter flower display and does nothing to address the buildup of old foliage within the plant.

New Zealand wind grass (Anemanthele lessoniana). This evergreen, or shall I say ever-orange plant is absolutely stunning when it’s happy – but wind, heavy soils, and simple time can cause a buildup of beigey-brown leaves that make your plant look sorrowful and half dead. Unfortunately, New Zealand wind grass does not respond well to being pruned to the ground, and if it comes back at all from such a treatment, it will do so quite slowly. Another alternative is to grab small fistfuls of primarily dead leaves and cut them out as close to the base as possible. This stimulates new growth, and by moving around the plant and pruning out about 20 fistfuls of dead leaves every two months for a year, you will effectively rejuvenate the plant and give it new life.

Switch grass (Panicum) and fountain grass (Pennisetum). These grasses are satisfyingly easy. Use your handheld hedging shears or a Japanese trimming sickle and cut these plants about 5 inches from the ground in January. The one exception are colored fountain grasses such as ‘Rubra’, ‘Fireworks’, or ‘Cherry Sparkler’, none of which appreciate our winter frost and rain. I generally treat them as annuals, but if you are hoping to overwinter them, leave them alone until you can see whether or not they are coming back in spring, because the old foliage will shelter the growth points and help them through any frosty nights. Once you see new shoots sprouting up at the very base, you can cut out the old foliage, being careful not to remove any new growth with it.

Mexican feather grass (Nassella tenuissima). These grasses don’t need to be pruned every year, but when they do need it they can be pruned at any time of year you wish. When they are ready, they will develop shaggy beige dreadlocks which rival that of a Humboldt hippie, and may begin to flop. I generally end up pruning them every two years in August after bloom. Wear sturdy jeans, and a workshirt that the seed heads won’t cling to, because (trust me on this) the seed heads do not come out easily in the laundry and the incautious gardener will be picking itchy seeds out of their soft fleece for months.

Japanese forest grass (Hakonechloa) and Japanese blood grass (Imperata cylindrica). This is another easy set of grasses. You can prune them at any time between when they go fully brown in November, and when their new growth begins to emerge in March. Just use your handheld hedging shears or pruning sickle to bring them down to about 2-3 inches tall, just as you would a dormant perennial flower.

Blue oat grass (Helictotrichon). While I love the spiky habit and strong blue color, blue oat grass piles up so quickly with dead beige strands that it quickly overwhelms the look of the plant. Here’s my quick solution for getting them back on track: put on rubber gloves, and run your fingers through the grass as though you were combing its hair. The spent foliage comes out in easy clumps. You may need to do this quarterly to keep the plant looking good. However, this plant doesn’t respond well to being pruned to the ground, and may rot out in clumps if you whack it frequently.

Sedge (Carex), lily turf (Liriope) and mondo grass (Ophiopogon). These plants really don’t need to be pruned much at all, and can look good indefinitely without anything more than occasional deadheading (for Liriope). However, if painters or the family dog tramples your plants, or if time causes some browning of the foliage, you may need to go in for the big chop. In early to midspring, use your hand pruners or hedgers to remove two thirds of the foliage. Though your plants will look awkward at first, they should look good again within 2 to 3 months. However, because this type of pruning weakens evergreen grasses, it shouldn’t be done any more often than is necessary to keep them looking good.

Sweet flag (Acorus). This plant is very similar to sedge, lily turf, and mondo grass in the way it is pruned, yet there is one important difference. Sweet flag tends to spread out laterally and cover the ground in a wide, tight clump of very thick rhizomes. If you would like to make the plant into a smaller clump, you can grasp a handful of foliage around the outer edge of the clump and pull towards the center of the plant. The most recently rooted rhizomes will pull up easily and it’s a simple matter to cut off any of those outer rhizomes by snipping them off as close to the base of the plant as possible. If you go all the way around the plant, lifting the outer edges of the clump and trimming out each rhizome, you can effectively make the plant much smaller around, and an added benefit is that you will have a small pile of lightly-rooted sweet flag to plant around the garden or give to friends. This can be done at any time of year.

Blue fescue (Festuca ovina var. glauca, more). I think of blue fescues as short-lived, because they eventually pile up with a great deal of dead foliage if they aren’t pruned and divided every few years. While I certainly don’t object to a spot of pruning, I find division tiresome, both because of all the digging and because of the uncertainty about whether your newly divided plants will make it. However, if you don’t want to replace your fescues every 5 to 7 years, consider getting on a schedule of pruning every other year by removing half to two thirds of the foliage in midspring, and dividing every 3 to 4 years.

The right tools for pruning grasses

While selective pruning is always done with hand pruners, cutting grasses to the ground is a different matter because of the sheer number of stems you need to trim all at once. Even with small grasses such as Japanese forest grass or Mexican feather grass, using hand pruners requires so many cuts that it makes this fun seasonal task seem like an arduous chore. Here are my favorite tools to get the job done right.

Fiskars PowerGear Hedge Shears, or Fiskars Quantum Hedge Shears. Hedging shears are an ideal tool for cutting large and small grasses down to the ground. Though most hedge shears are designed to do a precise job of cutting tiny leaves and stems, such as those of boxwood, these particular models are built for heavy-duty jobs where you’re cutting thicker stems. This line of shears from Fiskars have a gearing mechanism which provides leverage to help you power through cuts, and the blades have a nonstick coating so they slice through even the largest ornamental grasses with ease. The Powergear version is the regular workaday version, while the Quantum model is the high-end one that does essentially the same thing but feels much more luxurious to use.

Battery-powered hedging shears. While you may have tried some battery-operated power tools in the past and found them lacking, there’s a new generation of 40 V cordless power tools which are quiet to run, avoid the mess of gas and oil, and work great for about an hour on each charge. This 24 inch one from Black & Decker is the model that my landscaping crew uses on our jobs (spare batteries here), and I think my clients appreciate that it doesn’t make a racket, and is less stinky than the traditional gas powered hedger. These are perfect for grasses like Miscanthus – tie your grass into a bundle and zip through the foliage in seconds with this bad boy.

Serrated Japanese sickle. A sickle is a traditional harvesting tool which has a handle attached to a curved, serrated blade. To prune a grass, hold the foliage taut with one hand and use the other hand to run the sickle’s toothed blade against the base of the plant using a sawing motion. Because you’re already holding each clump of foliage, you can put trimmings into a bag or bucket as you prune, saving time on cleanup. Sickles aren’t as effective on the thicker stems of large ornamental grasses, but are a time-saving solution for small to medium grasses. I like this one from Garrett Wade.

Want to learn more?

Here are some previous articles I’ve written about pruning different types of ornamental grass.

Pruning Miscanthus and other large grasses

How to summer prune Miscanthus and other large grasses

Stop! Don’t prune that grass (How to prune ornamental grasses right)

How to prune a variety of ornamental grasses

What’s Growing On: Proper pruning of ornamental grasses and look-alikes

I have to admit, this article is about one of my pet peeves, plant butchering. I hope to educate homeowners and commercial landscapers about how the specific growth habits of different plants should dictate the appropriate pruning methods.

If you remember only one rule from this article, it should be this: Some plants should NOT be sheared into unnatural balls or boxes!

This caveat especially applies to tall grass species and similar plants. Their leaves are showy, and if they’re chopped halfway off, the attractive form of the plants will be ruined permanently or for many years to come. If grasses are “shaped” like hedges, the result is unsightly, ragged balls of half-length leaves from which the points of longer, newly emerged leaves stick out, looking like a horrible haircut.

Ornamental grasses and other plants with a similar appearance have characteristically long, narrow, straplike leaves, and they’re frequently used as focal points in a landscape. Depending on the species, their foliage can be stiffly upright, gracefully arching, or tufted. They don’t have branches with leaves scattered along their length; instead, their leaves all emerge like a fountain from a central, ground level clump or “crown.” Their leaf buds are at the root-shoot junction at or near the soil level.

So how should these plants be properly maintained? Let’s start with the grasses.

Ornamental grasses can be grouped into two categories: warm season and cool season. Each has different pruning needs.

Warm season ornamental grasses

Warm-season grasses grow best at temperature between 80 and 95 degrees Fahrenheit. They grow robustly during spring and summer, flower in fall, and go dormant from late fall through early spring. Some commonly planted decorative species of warm-season grass include Deergrass (Muhlenbergia rigens), Blue Grama (Bouteloua gracilis), Fountaingrass (Pennisetum species), and Maiden Grass (Miscanthus sinensis).

As a general rule, warm-season grasses need a pruning only once a year or less. Oftentimes, they can be “combed” with gloved hands or with a small rake to remove dead leaves and neaten their appearance, without the need for severe pruning. When grooming the plants, start at the base, then pull upward to remove old growth. If necessary, the clumps can be renewed by cutting them down to a height of 2 to 4 inches (not flush to the ground, to protect the crowns).

The best time to cut back warm-season grasses is in late winter or very early spring, just before fresh leaves begin to emerge. (The exact timing of new growth depends on climate and precipitation.) The exception to this seasonal trimming rule is if you live in a fire-prone area; in this instance, cut back dried grass clumps in the fall, and protect their tender crowns with a layer of loose organic mulch.

Warm-season grasses are best undisturbed through winter. Their dried flowering stalks, seedheads, and leaves change color to subtle shades of golden-brown, tan, and white during dormancy, adding a decorative touch and visual interest to the winter garden. The old leaves also protect the tender crown of the plant from frost damage, and they provide shelter for birds and beneficial insects.

Cool season ornamental grasses

Cool-season grasses favor temperatures between 60 and 75 degrees Fahrenheit. They begin new growth as temperatures drop in the fall, and they prefer more moisture than warm-season grasses. Many cool-season grasses flower in spring and stop sending out new growth in summer. In our mild climate they grow year-round, although their growth slows significantly in heat. Some common ornamental cool-season grasses include Feather Reed Grass (Calamagrostis x acutifolia), Blue Fescue (Festuca glauca), and Blue Oat Grass (Helictotrichon sempervirens).

Periodic upkeep to remove dead leaves and spent seedheads is sufficient to keep these grasses attractive for many years, without trimming/pruning. Use the same grooming method as with warm-season grasses.

Cool season grasses often don’t need cutting back unless the foliage is damaged or dominated by old leaves. If it’s necessary to renew these grasses, cut them down by about 2/3 before the fall growth spurt, or early in summer if fire danger is a consideration. Trimming cool-season grasses too severely or frequently or at the wrong time of year — such as during peak fall and winter growth or during severe cold weather — will stress the plants and make them more susceptible to disease or frost damage. Once new growth fills in, the older, shortened leaves can be selectively cut out with pruners to improve appearance if needed.

Cool-season grasses are also pretty in winter, when cold temperatures often leave their foliage tinged with hues of bronze, purple, red, or gold.

Some final notes

Make sure your pruning tools are clean and sharp to prevent disease and ragged cuts. Hand pruners work well for small grass species, but if you have large grass clumps to cut back, use manual hedge shears, electric hedge trimmers, or a weed trimmer fitted with a blade attachment.

One useful trick is to bind the leaves of each grass clump together before pruning; this keeps them out of the way and makes cleanup easy. If you use natural jute twine instead of man-made materials, the entire bundles can be composted or put in green waste bins.

Some excellent sources of information on ornamental grasses and their care are:

• “The Encyclopedia of Ornamental Grasses” by John Greenlee.

• “Pruning Ornamental Grasses,” an online article by the UC Master Gardeners of Sonoma County.

• A short YouTube video (https://youtu.be/nuQEw_umiz0) entitled “Pruning Ornamental Grasses” by the University of Illinois Extension.

Next month, we’ll take a look at how to properly maintain grasslike plants.

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