DRIVING NORTH on Highway 1 from Stinson Beach to Tomales, one can't help but be dismayed by the spreading clumps of one of California's most invasive plants: pampas grass (Cortaderia jubata).
These large, handsome plants grow to 8 feet in diameter and height, each with spikes up to 15 feet, capped by striking fluffy, pale plumes in late summer. Typically, they grow in groups, probably seeded from a local "mother" plant. Since each plume produces thousands of seeds that can be carried by winds up to 20 miles, pampas grass spreads quickly. It establishes itself easily in disturbed, open earth, which is why it is so common along the embankments of our coastal roadways. Once firmly established, it will completely choke out native and other plants, and provide neither food nor cover for wild life.
Its long, frondlike dark green leaves, about an inch wide, are serrated and sharp, making it hazardous to work around these plants. The rugged root systems of large mature plants require heavy equipment to remove them mechanically. It's unfortunate that such a spectacular and hearty plant is invasive, for otherwise it might be an elegant addition to our gardens. As it is, it is important to avoid planting it, and to remove it from public and private gardens and roadways as aggressively as possibly. Fortunately, the seeds of Cortaderia jubata rarely live more than a year or two, so once removed, it is relatively easy to keep under control.Ê
A companion plant and look-alike is Cortaderia selloana, which comes in various forms and is sometimes found in nurseries. While not as invasive as Cortaderia jubata, Cortaderia selloana is, indeed, invasive, and unless planted in a highly protected space with little chance that its seeds could blow over the fence, it is wise to avoid it. The latest Sunset Western Garden book cautions against using it and recommends removing it from gardens that border wild lands.
For the past year, I've been involved with an effort sponsored by the Inverness Association to remove pampas grass from the embankment along Sir Francis Drake Boulevard in Inverness. Last summer, we hired a professional landscaping contractor to cut back the blooming stalks, to prevent further spread of seeds from existing plants in this immediate area. This summer, we plan a more thorough eradication of established plants, accompanied by outreach to local residents, organizations and our sister West Marin villages. Our goal is to engage as many others as possible in removing pampas grass from our bit of California's coastline. Invasive plants on the scale of pampas grass cannot be controlled without the cooperation of many private and public entities, especially gardeners. In the process I've learned how difficult it is to eradicate this tough, invasive plant.
Eradication and control come in two forms: chemical (herbicide) or mechanical.
Since the county of Marin does not permit the use of herbicides along County roads, nor would the residents of the Inverness Ridge approve using herbicides in this area, this leaves us with mechanical methods for use along Sir Francis Drake Boulevard.
Following the advice of Ellen Hamingson, restoration biologist with the Point Reyes National Seashore, we plan again to hire a landscape contractor to cut back existing plants to within a few inches from the ground, likely with chain saws. The stubby plants remaining will be enclosed tightly with plastic and left to die. We considered digging/pulling the plants out, but the embankment is very steep, the plants are as much as 30 feet above the road, and the resulting holes would certainly cause erosion. Our hope is that native vegetation will take hold while the pampas grass plants die, likely within a year, depending on the weather. Warm is better. We may choose to reseed the area, if we have enough funding.
Removing pampas grass in areas not accessible to heavy equipment can be done by hand, using a mattock or similar tool. This is done within the seashore in wilderness areas. Plants are cut back, quartered, and removed from their holes. Plumes are placed at the bottom of the holes, and the plant returned to the hole upside down, so the roots are exposed to sun and air. I've read of whole plants left in tree branches to dry out and die. Once an area is cleared of pampas grass, it is relatively easy to monitor and control future growth. Small plants, those less than two feet in diameter, are not difficult to remove.
Herbicides (such as Roundup, a broad-spectrum weed killer) are effective in killing pampas grass, though must always be used with caution, to ensure that spray containing the herbicide does not touch other plants and does not enter the soil. In home gardens, it is advisable to try mechanical methods before resorting to using an herbicide.
One study found good results using an application called "ropewick treatment," which applies herbicide with a wick or sponge attached to a "well" of herbicide. None of the nurseries I contacted had heard of this device. It would permit the application of herbicide directly to the leaves of the plant, which can also be done (carefully) with a paintbrush. Using herbicide in either summer or fall is advised. One study recommended cutting back fronds/leaves in early summer; as new growth appears in late summer, use herbicide on the new growth. This method requires less herbicide.
For me, it is a challenge to write a garden article about all the ways to kill what is actually a stunning plant. I would rather write about growing things, so here is a short list of plants that have the scale and vertical heft of pampas grass that you might consider as substitutes in the garden:
- Stipa gigantea: one of the tallest, most graceful grasses with showy plumes in summer.
- Phormium (New Zealand flax): The larger forms are dramatic and come in various colors.
- Miscanthus 'Giganteus' (giant silver grass): spreading, upright 8 to 12 feet late summer blooms.
- Miscanthus transmorrisonensis (evergreen Miscanthus): 4-foot leaves with 4- to 6-foot flowering stems.
- Palms: the shorter varieties, branching close to the ground, offer dramatic focal points.
The University of California Marin Master Gardeners are sponsored by UC Cooperative Extension. For questions about gardening, plant pests or diseases, call 499-4204 from 9 a.m. to noon, and 1 to 4 p.m. weekdays, or bring in samples or pictures to 1682 Novato Blvd., Suite 150B, Novato.