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RAVENNA GRASS A NOXIOUS WEED ESCAPEE FROM GARDENS

GARDEN TIPS – written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written August 6, 2015

RAVENNA GRASS A NOXIOUS WEED ESCAPEE FROM GARDENS

Most gardeners I know are concerned about the environment and would be upset to learn that about half noxious weeds in this country were introduced by gardeners like themselves. Gardeners are always excited to find an interesting or unique new plant for their yards and gardens. Unfortunately, some of these plants escape the confines of the garden and wreak havoc on wildlife habitat and agricultural lands.

One of these escapees is Ravenna grass (Saccharum ravennae), a large “ornamental” grass, also called “hardy pampas grass” or “plume grass.” It is so named for its resemblance to pampas grass, forming large 3 to 4 feet diameter clumps and producing 12 feet tall flowering stems topped by attractive silver feathery plumes. Unfortunately, the plumes produce plenty of minute seeds that are easily in spread wind and water.

Ravenna grass proliferates in gardens, irrigation drainage ditches, wetlands, and riparian areas where it can crowd out habitat, create impenetrable areas, and restrict stream flow. It could become a problem in eastern Washington along the Columbia and Yakima rivers and is already a serious problem in many other western states.

Where did it come from? Ravenna grass is native to the Mediterranean region and has been sold by the horticulture industry since about 1921 as a desirable ornamental grass. In fact, a quick search of the internet indicates that you can still buy it. Fine Gardening magazine touts its height as a striking vertical accent for the landscape and notes that it is deer, drought, and frost tolerant. Nevertheless, do not to buy it or plant it. It will spread via the seeds and become a weed problem in your yard, your neighbors’ yards, and beyond.

Our local Master Gardeners unsuspectingly planted some Ravenna grass several years ago in the Ornamental Grass garden of their Master Gardener Demonstration Garden. It thrived and spread itself throughout the entire garden and the neighboring library landscape. They were clued into this invasive grass by a local noxious weed board employee who advised seeking out all the plants in the garden and digging them out. (Ravenna grass is classified as a Class A noxious weed by the Noxious Weed Board of Washington, requiring all of us to remove it from our land.)

Before they could attack the Ravenna grass infestation, the Master Gardeners needed to know its identifying characteristics. Without the flowers or seed heads, it is often hard to tell one ornamental grass from another. However, Ravenna grass leaves are distinctive with a white mid-vein running the length of the 0.5 to 1 inch wide and 3 to 4 feet long blades. The blades are blue-green in color with very hairy bases.

Once they knew what it looked like, the Master Gardeners were ready to attack the grass by digging it out the plants and their roots because that is the most effective method of control in gardens and landscapes. There are not yet recommended chemical control recommendations for controlling Ravenna grass in home gardens.

The Master Gardeners found and removed over 200 smaller plants not yet producing flowers and seed along with the offending larger plants originally planted in the Ornamental Grass garden and responsible for the problem. They averted a noxious weed disaster in their garden, but this grass was unknowingly bought and sold to many other gardeners in our state before nurseries were made aware of the problem. If you have “hardy pampas grass” in your landscape, check it out, and get digging if you find that it is Ravenna grass. For more information on Ravenna grass consult the Noxious Weed Control Board of Washington at: http://www.nwcb.wa.gov/detail.asp?weed=193

PAMPAS GRASS GOOD OR BAD?

written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

We can blame ourselves as gardeners for some of the troublesome weeds in our yards, gardens, roadsides and natural areas. Many noxious weeds are non-natives that were brought into this country as ornamental garden plants that later escaped. They now threaten native wild plant and animal life or cause us trouble in our gardens and landscapes.

Pampas grass is one of those non-natives ornamentals that has escaped. While some will adamantly avow that pampas grass isn’t invasive, others will swear that it’s already a serious invasive weed in parts of the US. Part of this disagreement is the result of the confusion resulting from the two related types of grass commonly called pampas grass. One is the common garden pampas grass (Cortaderia selloana) that has been considered non-invasive and its close relative is Jubata grass or Andean pampas grass (Cortaderia jubata) that’s known to be highly invasive. Both are native to South America.

The Andean pampas grass is the “bad” cousin of the two. It’s very aggressive in open ground that’s bare or has been disturbed. In California, Andean pampas grass is a serious concern in coastal areas. The seeds of this grass develop without pollination and the plant readily seeds itself. The “good” cousin, the garden pampas grass, has been considered non-invasive in the past. That’s because it’s dioecious with separate male and female plants. For viable seed to occur, the female flowers need to be pollinated with pollen from male flowers. Because the female flowers or plumes are whiter and showier, nurserymen and gardeners have traditionally only grown female plants. These are easily propagated by vegetative divisions of other female plants.

As long as male plants aren’t grown in the same area, few viable seeds are produced and the garden pampas grass is not invasive. However, in recent years some unwitting or unscrupulous nurseries have propagated garden pampas grass from seed and sold the resulting plants not knowing if they’re male or female. This has resulted in more of the male plants being planted and has resulted in this “good” cousin becoming very invasive in areas of California, Hawaii, as well as other areas.

In warmer regions it’s understandable that garden pampas grass can thrive. However, as a warm-season grass rated as hardy to USDA Zone 8, it shouldn’t survive and grow well in colder regions, but it does. In warmer climates it’s leaves stay green during the winter, but in colder climates they turn brown in winter like many other ornamental grasses. The plants will survive down to 10 degrees Fahrenheit and the crown will only be killed if the soil freezes deeply during the winter.

Personally, I think the term “garden” pampas grass is a misnomer. This ornamental grass is not for the ordinary garden. The clumps can grow up to five feet wide. The plants may grow to ten feet tall with flower stalks with plumes reaching to 12 feet tall. It takes about three years before it produces flowers. In late winter, the plants are cut back to about 18inches from the ground. This is no easy task! The edges of the leaves are extremely sharp and the plant is very dense. The best tool for cutting it back is a small chainsaw. That’s what I call extreme gardening!

Of course, like with so many garden plants, there is a dwarf form of this gargantuan grass. It’s dwarf pampas grass, Cortaderia selloana

Pumila

. Keep in mind though that “dwarf” is a relative term. Dwarf pampas grass plants reach a size of 4 to 6 feet wide and 5 feet tall. It produces 10 foot long flower stalks with silvery white plumes. Once established, it does well in scorching sun and tolerates drought and wind. It’s also hardy down to USDA Zone 6. This one is also cut back to 18 inches from the ground in late winter with a chainsaw!

There’s also another grass that’s commonly referred to as pampas grass. The hardy pampas grass (Saccharum ravennae, previously known as Erianthus ravennae) is not related to the bad and good “cousins”. The hardy pampas grass is native to north Africa and the Mediterranean. It resembles true pampas grass with plants that grow 6 feet wide and 10 to 15 feet tall with silvery white flower plumes that look somewhat like the fluffier pampas grass plumes. There are also concerns about growing this grass because it’s already shown itself to be invasive in parts of the West.

Environmentally conscientious gardeners should avoid planting any of the pampas grasses. They pose potential threats to our native wildlife, plus they’re pretty big for the average gardener to manage. I know I won’t be planting one anytime soon. If it becomes a noxious weed here, I don’t want to have that on my gardening conscience.

Published: 11/15/2008 1:34 PM

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