Garden Tips: Gardeners to blame for half of noxious weeds

Most gardeners would be upset to learn that about half of the noxious weeds in this country were introduced by gardeners like themselves. Gardeners are always excited to find an interesting or unique new plant. Unfortunately, some of these plants escape 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 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 Internet search shows 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.

Our local Master Gardeners unsuspectingly planted some Ravenna grass several years ago in the ornamental grass garden of their Demonstration Garden on Union Street in Kennewick . 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 finding the plants 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 hairy bases.

The most effective method to control Ravenna grass is to dig it out by the roots. There are not yet recommended chemical control recommendations for controlling Ravenna grass in home gardens.

The Master Gardeners found and removed more than 200 smaller plants not yet producing flowers and seeds 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 other gardeners in our state before nurseries were made aware of the problem. For more information on Ravenna grass, go to the Noxious Weed Control Board of Washington at www.nwcb.wa.gov/detail.asp?weed=193.

This story was originally published August 6, 2015 at 9:00 AM with the headline "Garden Tips: Gardeners to blame for half of noxious weeds."