Gardening Answers Knowledgebase

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, at the following link:
http://www.co.thurston.wa.us/health/ehoss/landscp.html

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.

Season All Season
Date 2008-01-03
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Regrettably, there are not any native, shade-loving, walkable ground covers available unless you are interested in mosses. If that is appealing, you can check in the book Plants of the Pacific Northwest Coast by J. Pojar. The following websites may help you find native plants:
King Conservation District
King County Native Plant Guide
Washington Native Plant Society

For information on growing mosses, see "Encouraging Mosses" from Oregon State University, based on the writing of George Schenk.

If your heart isn’t definitely set on natives, there are some good alternatives:

1. In her book Big Ideas for Northwest Small Gardens, Marty Wingate recommends “Mazus reptans.” It is semi-evergreen to evergreen with tiny blue flowers from late spring through summer. It takes full sun to part shade and is delicate looking, but takes foot traffic. It requires some fertilizer to stay perky. (Note: I use it in my garden--it is versatile and pretty)
2. Another source of ideas is the website http://stepables.com/
   Click on “plant info,” then “plant search.”
3. A ground cover that I have found useful (it can take car traffic a couple times a day) is “Leptinella gruveri Miniature.” You’re almost certain to find it at the website above.

Season All Season
Date 2008-01-31
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I am guessing that the spot receives a good amount of sun, since you have lavender Lavandula that flowered there in the summer. Were you looking for a groundcover that will tolerate people walking on it, or did you want somewhat taller plants that will blend well with the lavender?

If you plan to walk on the area, you might want to consider chamomile (Chamaemelum nobile) or creeping thyme (Thymus serpyllum).

There are many great choices for plants not intended to be walked on, and I recommend that you take a look at some of the resources we have in the Miller Library so you can find the plants that most appeal to you. I recommend the books Gardening with Groundcovers and Vines by Allen Lacy (HarperCollins, 1993), and Perennial Groundcovers by David MacKenzie (Timber Press, 1997) as starting points.

Plants that are evergreen (or 'ever-grey') and might go well with lavender are Santolina, Helianthemum (sun rose), Teucrium chamaedrys (germander), and Ceanothus thyrsiflorus (creeping blue blossom ceanothus).

For the spot under your pine trees, you will need plants that tolerate shade and do not have large root systems. I would try Lamium (dead nettle), which comes in several foliage and flower colors, and I would avoid Lamiastrum, a closely related plant which is very aggressive. Vinca (periwinkle) might also work. The Lady Bird Johnson Wildflower Center has information on planting beneath pine trees.

Season All Season
Date 2006-11-14
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Here are some links to information which may be useful to you:

Primitive Plants: Mosses, Ferns, and Allies

Moss cultivation:

Encouraging Mosses

Mad About Moss—The Simple Art of Moss Gardening

There are two books I would recommend, Moss Gardening by George Schenk (Timber Press, 1997), particularly the chapter on "Moss Carpets," and How to Get Your Lawn Off Grass by Carole Rubin (Harbour Publishing, 2002). Rubin gives directions for preparing your site, which involve digging out existing plants or--in your case--smothering the lawn with mulches of leaves (12 inches), bark (3 inches), or newspaper (10 sheets thick). Schenk offers several different methods for creating a moss garden. Briefly paraphrasing, these are:

1. Work with nature, allowing self-sown spores of moss to take hold. (Prepare the site by weeding, raking, and perhaps rolling the surface smooth.)
2. Encourage the moss in an existing lawn by weeding out grass. You can plant what the author calls "weed mosses" which will spread, such as Atrichum, Brachythecium, Calliergonella, Mnium, Plagiothecium, Polytrichum, and others.
3. Instant carpet: you can moss about 75 square feet if you have access to woods from which large amounts of moss can be removed legally.
4. Plant moss sods at spaced intervals (about one foot apart) and wait for them to grow into a solid carpet.Choose plants that match your soil and site conditions.
5. Grow a moss carpet from crumbled fragments. This is rarely done, and only a few kinds of moss will grow this way, including Leucobryum, Racomitrium, and Dicranoweisia.

Another approach is to change the soil pH. Sulphur should be beneficial to moss and detrimental to lawn grass. The reason for this lies in the fact that moss grows best with a soil pH of 5.0-6.0, while lawns grow best with soil pH between 6.0 and 7.0 (according to The Lawn Bible by David Mellor, 2003). Added sulphur lowers the soil pH, creating a more acidic environment.

Season All Season
Date 2007-04-04
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Some of the plants that occur to me, based on the description of your site, are Brunnera macrophylla, Epimedium, Geranium phaeum, Stachys byzantina, Lamium maculatum, and Liriope. Of these, the Geranium and Lamium will trail somewhat, while the others are essentially upright.

These links offer lists of plants that may be appropriate to your site: From the University of Missouri Extension and Whatcom County Groundcovers.

You could also try entering your site requirements into the plant-finding and plant selection web pages below:

Great Plant Picks (a local site)

King County's native plant guide

Missouri Botanic Garden Plant Finder

Royal Horticultural Society Plant Selector

The Miller Library has many books on gardening in the shade, so you may wish to come in and do some research to help you in your plant selection. Here is a booklist that may be of interest.

Season All Season
Date 2007-05-21
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Creeping thyme would be ideal for your needs. It will do well in sun, and can withstand foot traffic. Colorado State University Extension has useful information on groundcover plants for dry conditions.

Leptinella, or brass buttons, is another option.

Chamaemelum nobile likes sun and will withstand light foot traffic.

The website for Stepables, a company specializing in groundcover plants, allows a search by plant characteristics.

Season All Season
Date 2007-07-25
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If it's pure gravel, you can just make a border (with rocks and/or wood, preferably non-treated) and fill it with 9-12" of soil. (No need to remove the gravel.) You buy soil by the cubic yard, so to figure out how much, multiply the length (feet) x width (feet) x depth (.75 or 1), then divide by 27 to get the number of yards. One yard of soil is 3' x 3' x 3', or 27 cubic ft. My guess is that you need less than a yard, but it settles.

You can save money by buying the soil in bulk. Otherwise, you have to buy it by the bag, and they might come in cubic feet. If there is only some gravel, you may be able to get by with the soil/gravel mix that you have. See how much hardpan there is by digging around a little.

If you have lots of weeds in the gravel, cover the whole area with large sheets of cardboard or multiple layers of newspaper (about 10 sheets), overlapped to prevent light from getting through. Then put down a border and fill the area with soil. Smothering weeds depends upon complete darkness more than anything. Therefore, overlapping biodegradable stuff and deep soil is key.

Once you've done that, you can plant right away. Here are some plant suggestions. I've included links to pictures, but you can always find more on Google images or the Missouri Botanical Garden's PlantFinder

1. Lobularia maritima, known as sweet alyssum: You can plant seeds of this and it will come up this year. It's best to mix it with something else, since it dies down in winter (but self-seeds vigorously and will return). The white seeds the fastest (year to year), but it's nice to mix with purple. Both varieties smell good and attract beneficial insects.

2. Fragaria x ananassa 'Pink Panda': A strawberry-potentilla hybrid that grows fast and spreads easily, is good weed suppresser, and blooms twice a year with pink flowers. This is an excellent groundcover, will probably be evergreen.

3. Pachysandra: This plant is evergreen, and though it is not as fast growing as some groundcovers, it does spread.

4. Hardy Geranium spp.: Geranium x oxonianum 'Claridge Druce' is a variety that spreads well. Another good variety is Geranium endressii 'Wargrave's Pink'; in particular, it seeds itself well. Geranium macrorrhizum has many cultivars, a pleasant scent, and self-seeds readily.

5. Galium odoratum: Also called sweet woodruff, this plant is prettily scented, probably evergreen here, and spreads fairly rapidly. It produces white flowers in early spring, and it would be particularly good to mix with something taller, like Geranium species.

6. Oxalis oregana: This native plant looks like a shamrock, and though it is slow to establish, once it has it's very tough and spreads. If you don't get the native Oxalis oregana be careful, as the other species are very aggressive.

7. Euonymus spp.: These woody groundcover plants are evergreen, and come in lots of varieties like E. fortunei 'Emerald 'n'Gold' and 'Emerald Gaiety'. Do be sure to get a groundcover and not a shrub version of the plant. 'Emerald and Gold' is the most robust choice.

8. Convallaria majalis: Also known as lily of the valley, this is a vigorous groundcover.

9. Maianthemum dilatatum: Called false lily of the valley, this native plant is a good choice for shade groundcover.

10. Polystichum munitum: The native swordfern (or another fern species) might work. P. munitum is basically evergreen, though you might need to cut out some dead fronds in late winter, and makes a good mix with something else. Other deciduous ferns are higher maintenance.

There are also a couple of plants to avoid!

1. DON'T plant Aegopodium podagraria 'Variegatum': Commonly called bishop's weed, and frequently used as a groundcover, this plant is very invasive.

2. DON'T plant Lamiastrum galeobdolon, either: Yellow archangel is very invasive in Pacific Northwest forests.

Season All Season
Date 2008-05-14
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