Ornamental grasses and their risk of reseeding

I have neighbors who are asking questions about ornamental grasses and their risk of reseeding. They are specifically interested in Pennisetum ‘Hameln’ and Cortaderia ‘Richardii.’ I have known Stipa (Nassella) to reseed but I have never noticed any reseeding from either of these two groups in the Seattle area. I know they can reseed freely in other parts of the country, but I suspect the seeds rot in our winters. How can I find out?

I consulted online lists of invasive species and found a few references to Pennisetum species (but not the cultivar you mention) which are problematic in Oregon and California.

According to the University of Florida Extension, the variety Pennisetum alopecuroides ‘Hameln,’ is not known to be invasive.

Although not classified as invasive, the species P. alopecuroides is still a spreader by self-sowing. Rick Darke, author of The Encyclopedia of Grasses for Livable Landscapes (Timber Press, 2007) and a Pennsylvanian, says it “self-sows, usually at a manageable level; however, some of the fall-blooming varieties such as ‘Moudry’ and ‘National Arboretum’ are particularly fertile and can be very weedy if conditions are suitably moist. They often become established in irrigated cool-season turf.”

The Royal Horticultural Society plant profile for ‘Hameln’ says it is early-flowering (which might mean that seeds have time to establish themselves, though a droughty summer such as we sometimes have in the Seattle area might prevent this).

One sterile cultivar is Pennisetum advena ‘Rubrum’.

As with Pennisetum, there are species of Cortaderia (C. selloana, C. jubata) which are listed as invasive in various parts of the world. Here is an excerpt from Los Angeles & San Gabriel Watershed Invasive Plant-Monitoring and Outreach Program’s WeedWatch information on Cortaderia:

“It is unknown whether the cultivated and ‘sterile’ varieties of Cortaderia are able to cross with the wild species of Cortaderia and produce viable offspring. Until this scientific research is conducted, and considering the rampant ecological damage already caused by both C. selloana and C. jubata, it is not recommended to plant any members of the species, including cultivars, varieties and supposed ‘sterile’ varieties.”

Author Rick Darke says that all species of Cortaderia may be grown from seed (therefore, species are not sterile).

A Pacific Northwest palms and subtropical plant online discussion group, Cloud Forest, (no longer available online) includes some dialog on Cortaderia richardii:

“Another terrific grass is Cortaderia richardii, which is a NZ form of the humongous pampas. It is short (to 5 ft.) with elegant flowering pattern (circular and reaching instead of vertical). It’s evergreen and a great specimen. Needs a 6 x 6 space minimum. ”

“Cortaderias scare me a little, ever since my neighbor’s specimen seeded itself all over my poor rock garden (heck it is all over the neighborhood). Obviously sellowiana; I don’t think C. richardii is as aggressive. The other one is a devil to try to remove once it gets wedged in! The leaves cut like razor blades and the crown is extremely persistent. I actually think they look kinda grand, and if I lived on the coast I’d be willing to use them as windbreaks (which is how they got all over the place). I don’t think a hurricane would injure them.”
“Cortaderia richardii is the magnificent cousin of the monstrous pampas grass. Petite and elegant in comparison. Mine have never self-seeded. My friend’s seeded a bit. It may be hotter by his house.”

landscaping around septic systems

We have a new house that we have to landscape around. The biggest problem is that we have to be careful what we plan due to the septic system. It is an evaporation system, with two huge cement tanks buried under the ground in the front of the house and plastic pipes running through the side yard. We are planting grass in a rectangle right above the biggest bunch of the plastic pipes, but what can go around it or by the cement tanks that will not grow long roots and dig into it? In looking at the planting information on the packages and in my Western Garden Book, nothing seems to mention root depth.

Below is an article entitled What to Plant Over the Septic System by Mary Robson (originally published in her Regional Garden Column for Washington State University Extension, December 6, 1998):

“As more and more people move into rural areas, questions about septic systems and landscaping have become quite common. This column deals with some of the basics. A new brochure from Washington Sea Grant called: Landscaping your Septic System, offers considerable detail on the subject and provided much of this material.

“First, be sure that the septic field is clearly identified, and you know where the reserve area is. Keep all construction away from these areas. Understanding the functioning of the system is vital. Get information. (Some of it is available in video form.) The drainfield will not work well if overloaded with extra surface water, so be certain that it is not in the path of downspout run off or irrigation systems.

“Sunlight and air circulation also help the drainfield perform properly. Avoid surrounding it with tall trees. (Some shade is fine, but you would not plant an oak on the edge of a drainfield.) Set up some barriers so that it is not compacted by frequent foot traffic. Occasional mowing or moving through the field to check the system is certainly fine, but you do not want the drainfield in the middle of a heavily used path.

“There are advantages to using plants over the drainfield. Plants do help provide oxygen exchange and contribute to evaporation necessary in the drainfield area. Choose plants with shallow, non-invasive roots. You do not want breakage or damage in pipes from root intrusions.

“Grasses are most commonly recommended for the septic area. Lawn can be attractive. Do not overload the system by watering it a lot. Meadow grasses or a mixture of turf grasses like perennial rye and some broadleaf flowers (such as yarrow) can also look good and require little maintenance. Several mixes sold as Eco-Turf or Fleur de Lawn have these components.

“Small, shallow-rooted ornamental grasses (for instance, Festuca ovina
\’Glauca\’ 4-10 inches) can also be good looking. Very tall grasses like Stipa gigantea are not appropriate. Avoid over-active plants like English ivy (Hedera helix), which is becoming a menace in forested areas by moving in and stifling trees.

“Edible crops are not suggested. Vegetable gardening requires frequent cultivation, and digging in the drainfield area is inadvisable. Also, the brochure notes that: Sewage effluent is distributed through the soil in the drainfield area. Any root vegetables planted in this area may be directly exposed to septic tank effluent.

“Other possibilities are low-growing ground covers. Some, such as bugle weed (Ajuga reptans) and vinca (Vinca minor) grow vigorously and would fill in quickly. The native kinnikinnick (Arctostaphylos uva-ursi) grows well in full sun but is slow to establish. A mulch around the plants may help with weed control while the plants spread.

“The green growing layer over the septic tank helps the system to function, adds to the appearance of the landscape, and should, ideally, be set up to allow easy monitoring and maintenance. Keep landscaping simple and straightforward, remembering that the object is the good performance of the system.”

To get more information on septic systems, contact your local health department. The brochure Landscaping Your Septic System (pdf) is available through the Sea Grant Program.

Here are links to publications that might also be helpful:

Mounds: A Septic System Alternative

Understanding and Caring for Your Sand Filter System

Care and Feeding of Septic Tanks

Miscanthus growing conditions and its invasiveness status

I am looking for an ornamental grass that doesn’t get over 5 feet tall
and am wondering what are the growing conditions for Miscanthus sinensis
(Gracillimus)? How much sun does it need, will it spread and invade my
other plants, is it invasive in our area (Seattle)?

I found several cultivars of Miscanthus listed on the local web site Great Plant
Picks. Miscanthus sinensis ‘Morning Light’ will reach about 5 feet tall
by 4 feet wide. This Colorado State University Extension article on from ornamental grasses may give
you additional ideas on grasses for your garden.
Although the following link is for southwest Washington gardens, this
Washington State University list of ornamental grasses may be of use.
It includes Miscanthus sinensis ‘Gracillimus,’ and indicates it does not
have a problem with self-seeding.

Excerpt:

Miscanthus

BE CAREFUL! Many are self-seeding.

M. sinensis ‘Gracillimus’ Maiden grass 4.5′ FS Most popular. Seldom
self-seeds.

M. sinensis var. purpurascens Purple maiden grass, Flame grass 3 – 5′ FS
Gorgeous red-orange fall foliage. One of the earliest flowering varieties
of maiden grass.

M. sinensis ‘Silberpfeil’ Eulalia 4 – 5′ FS One of the hardiest varieties
of maiden grass.

M. s. ‘Morning Light’ Dwarf maiden grass 4 – 5′ S, LSh Arguably best
all-around plant of the Miscanthus group. Blooms late with reddish
flowers.

M. s. ‘Adagio’ Japanese silver grass to 3.5′ S, LSh Compact with
silver-gray foliage. Two- to three-feet long panicles emerge pink, fade
to white.

M. s. ‘Flamingo’ Japanese silver grass to 6′ Large, loosely open,
pink-tinted inflorescences. Slightly pendant blooms appear late summer.

M. s. ‘Sarabande’ to 6′ Similar to Gracillimus, but finer textured.
Golden copper colored inflorescences in August.

M. s. ‘Strictus’ Porcupine grass 4 – 6′ FS One of the hardier Miscanthus
cultivars. Tolerates wet soils.

M. s. ‘Variegatus’ Variegated silver grass 4 – 6′ S, PSh Prefers
moist, fertile, well-drained soil.

M. s. ‘Zebrinus’ Zebra grass 4 – 8′ S, PSh

Update from 2012 on the invasive potential of Miscanthus cultivars:

Wendy DesCamp of the Washington State Noxious Weed Control Board reports the following:
“There is now a record of the plant growing in eastern Washington by the Columbia River in Benton County. [described as follows:] Shallow backwater on N shore of Columbia River . . . below McNary Dam, elev. 85 m, 45 degrees, 55.9 minutes N, 119 degrees 21.4 minutes west. Collected by Peter Zika, 17 June 2011.

From what I can find, this is the first collection of naturalized Miscanthus sinensis collected in Washington.”

The State Noxious Weed Board is considering whether it should be added to the monitor list or not. The monitor list is a list of plants the Board is keeping track of to collect information and to see if the plants are occurring or spreading in Washington.

UW Botanic Gardens Director, Professor Sarah Reichard had this to say about Miscanthus sinensis:
“We have had it in the Soest Garden for years and I have not seen it invade and I am looking for seedlings. However, not invading in the artificial environment of a garden, with water and nutrient inputs means little for invasion in the wild. I have not heard of it being invasive here, and I have been paying attention to both this species and Imperata cylindrica.It might be a good addition to the [noxious weed] monitor list.”

transplanting Schizachyrium scoparium

Schizachyrium scoparium (Little Bluestem) seems to me to be difficult to transplant. They die on me when moved. What could I be doing wrong? The time of year? Adequately watered?

According to the Color Encyclopedia of Ornamental Grasses, Schizachyrium scoparium requires full sun, prefers good drainage or sloping ground, does not persist on highly fertile soils or in excessively moist conditions, and suffers if the crowns are crowded by mulch.

Propagate by seed or by division in spring.

Grasses are sensitive to soil level, especially when young. Ideally, the crown of the grass should sit just slightly above the soil surface. Planting too low can rot grasses and planting too high can cause them to dry out and die.

Mulch of all sorts can be an efficient method of controlling weeds and conserving soil moisture. Many species, such as Schizachyrium scoparium, cannot tolerate having mulch pushed up around their crowns, a practice that often promotes rot and disease at the base of the plant.

Source: Color Encyclopedia of Ornamental Grasses, by R. Darke, 1999, pp. 121, 276.

drought-tolerant native grasses

I am looking for a native, drought-tolerant grass for a small garden plot in Seattle. Can you suggest a grass that is 2-3 feet tall and at most 2 feet wide.

Native grasses that will do well in a dry meadow setting and grow 2-3 feet tall are:

Festuca idahoensis, Idaho fescue
Bromus carinatus and Bromus marginatus, brome grasses
Elymus glaucus, wild rye grass
Melica species, onion grasses
Calamagrostis nutkaensis, Pacific reedgrass

Each of these grasses grow in very distinct shapes–I recommend that you look at them before choosing which species to plant. Fescues are popular grasses for gardens because of their fine blades and pretty seed heads. Additionally, the Elymus and Bromus will grow much more quickly than the other species.

You can perform searches on each of these species at the USDA Plants Database by typing the plant name into the Plants Name search box–this database will give you additional information about the species and some pictures.

The Washington Native Plant Society website has a list of native plant vendors.

Carex species and difference between grasses and sedges

I was looking at the Great Plant Picks list of recommended grasses, and I wonder why they exclude Carex, which I find is such a useful plant in the garden.

Great Plant Picks does in fact list two different Carex species but they are not on the list of grasses because Carex is a type of sedge, and sedges are not grasses. An article entitled “Sedges Have Edges” from Hilton Pond Center for Piedmont Natural History has a detailed explanation of the differences among grasses, sedges, and rushes. All three are graminoids, but grasses are in the Family Poaceae, sedges are Cyperaceae, and rushes are Juncaceae. According to the article, “a simple ‘touch test’ is the giveaway for sedges, whose stems when rotated have a very noticeable triangular shape–hence a total of three ‘edges.’ ”

native Northwest beach grasses

I live in a community on Camano Island. We have some communal beach front property and would like to plant some native beach grasses that are about one foot high. What species do we have to choose from and where can we purchase them?

I found a list of native Northwest beach grasses in an online symposium moderated by Alfred Wiedemann of Evergreen State College in Olympia. (The symposium was about an invasive species, Ammophila arenaria, or European beach grass, which has been crowding out native species.) Here are some of the plants he mentioned:

Elymus (Leymus) mollis (Dunegrass)

Abronia latifolia

Convolvulus (Calystegia) soldanella

Carex macrocephala

Glehnia leiocarpa

Lathyrus littoralis

Poa macrantha

Here is a Seattle Times article from May 1, 2005 about beach plants by Valerie Easton that may be of interest to you. The Miller Library has the book that is mentioned in the article, Native Plants in the Coastal Garden by April Pettinger (Timber Press, rev. and updated, 2002), and it includes a list of native grasses. These two grasses were specifically recommended for beachside gardens:

Elymus or Leymus mollis (also listed above)

Festuca rubra (Red fescue)

Washington Native Plant Society might also be a good resource for you. They provide a list of nurseries in our area which specialize in native plants. King County’s Native Plant Guide also has a list of sources.

planting over septic drain fields

I am looking for plants suitable for a septic drain field site. I have a very large north facing slope in open sun with a drain field running along the top half. I would like to plant low to no maintenance ground covers and low growing shrubs to cover this area. This is a focal point when driving up to my house so I want it to be eye catching and interesting year round.

I thought of heaths and heathers as a possibility, but I’m not sure if the root system is shallow enough. I also would like to include native ground covers such as ferns, Gaultheria shallon and any others that you might think would work, as well as ornamental grasses and perennial flowers for interest. Can you please offer a resource for planting over drain fields or a list of plants that you think would work?

Trees or large shrubs should be kept at least 30 feet away from your drain field. If you do plan to plant trees near a drain field, consult an expert to discuss your ideas and needs. Trees and shrubs generally have extensive root systems that seek out and grow into wet areas like drain fields. Grass is the ideal cover for drain fields. Grasses can be ornamental, mowed in a traditional lawn, or left as an unmowed meadow. You can also try groundcovers and ferns.

The key to planting over the drain field is to select shallow-rooted, low-maintenance, low-water-use plants. When tank covers are buried, keep in mind that plantings over the tank–from inlet to outlet–will have to be removed every three or four years for inspection and pumping.

Planting your drain field will be much different from other experiences you may have had landscaping. First, it is unwise to work the soil, which means no rototilling. Parts of the system may be only six inches under the surface. Adding 2 to 3 inches of topsoil should be fine, but more could be a problem. Second, the plants need to be relatively low-maintenance and low-water use. You will be best off if you select plants for your drain field that, once established, will not require routine watering.

SOURCE: WSU Cooperative Extension – Clallam County

Information can be found here.

Thurston County, Washington, has some information about landscaping a drain field, including plant suggestions, here.

Additionally, the Pacific Northwest Gardener’s Book of Lists (1997, by R. & J. McNeilan) offers a number of groundcover lists for various situations, including groundcovers for dry sites, slopes, and sun and shade. The Miller Library has this book.

ornamental grasses that tolerate salt water

What ornamental grasses can I plant near salt water, and is there a local nursery that specializes in grasses?

As far as nursery sources, I think a full-service nursery is your best bet for finding ornamental grasses. The only “specialist” in grasses I could find is Walla Walla Nursery, which seems a long way from Seattle to go.

King County’s interactive native plant guide also includes a page on marine (salt water) shoreline plants. At the bottom of the page, note the three native grasses which are recommended:

Lyngbye’s sedge (Carex lyngbyei)
tufted hairgrass (Deschampsia cespitosa
dunegrass (Elymus mollis)

The following list of plants according to their salt tolerance comes from University of Minnesota Extension (link no longer available), but there may be some ornamental grasses that will do well here.

From the lists:

Calamagrostis acutifolia ‘Karl Foerster’ (Karl Foerster reed grass): high tolerance
Schizachyrium scoparium (Little bluestem): high tolerance
Elymus arenarius (Blue Lyme grass): high tolerance
Pennisetum alopecuroides (Fountain Grass): high tolerance
Festuca ‘Elijah Blue’ ‘Elijah Blue’ fescue: moderate tolerance

In her book Gardening at the Shore (Timber Press, 2006), Frances Tenenbaum lists a number of ornamental grasses (in addition to dune grasses):

Festuca glauca
Miscanthus sinensis
Muhlenbergia capillaris
Stipa tenuissima [now renamed Nassella tenuissima–in my experience, this grass is aggressive, seeding itself everywhere; the seedheads stick to people and pets who walk past it]

There are many attractive cultivated varieties of some of the plants listed above, and most local nurseries will carry them.

Garden Tip #50

A book by Jekka McVicar called Seeds: the ultimate guide to growing successfully from seed (Lyons Press, 2003, $22.95) will help you turn your seedy hopes into plant reality. Thirteen chapters are divided by types of plant including ferns, grasses, shrubs, perennials and herbs. The practical information that applies to all kinds of seeds, such as what type of soil to use, and how to break seed dormancy, is included in the last chapter. Color photos illustrate throughout.

For online tips for seed starting go to:
http://cru.cahe.wsu.edu/CEPublications/pnw0170/pnw0170.pdf from Oregon State University.