THE GRASS GROWS GREENER over the septic tank, or so Erma Bombeck famously maintained. I'm not so sure. My new home is on three and a half acres of rocks and trees, with a bit of lakeshore. The site, northwest of Kingston, Ontario, is all wild and lovely, except right behind the house, where a huge, flat-topped pile of sand and soil marks the septic system. The previous owner seeded it with grass, but that parched in the sun, so I'm turning to alternative ground covers and flowers.
For gardeners outside cities, septic tanks and septic tile beds are essential. However, as one installer of septic systems admitted, they can be "eyesores." If there isn't enough soil depth to bury the works, you'll have a hill of sandy fill near the house, skimmed with seven to 30 centimetres (three to 12 inches) of topsoil. It could be a big hill, about 12 metres wide (40 feet) and 18 metres long (60 feet), depending on the size of the house and its plumbing facilities.
It's inadvisable to plant anything but lawn over the septic tank, since it must be accessible for cleaning. However, any specimens with fibrous shallow roots that like well-drained soil can and should be planted on the tile bed. Artful plantings can help blend this cumbersome feature into its surroundings, while contributing to the aeration of the soil.
All flowering annuals are fine, whether plants or seeds. The seeds of vivid annuals, including cornflower, cosmos or poppy (shown above), can be scattered on bare soil, lightly raked in and watered until they sprout. This is an ideal spot for a wildflower meadow of native flowers and grasses, including little bluestem (Schizachyrium scoparium), which grows about 60 centimetres (two feet) tall.
Among perennials, consider ornamental grasses such as blue fescue (Festuca), feather grass (Calamagrostis) or ribbon grass (Phalaris), though the last can be invasive. Ground covers in sun might include the smaller veronicas, creeping forms of sedum, periwinkle (Vinca minor), bugleweed (Ajuga) or cotoneaster. In the shade, you might plant hostas, ferns or sweet woodruff. Taller perennials include yarrows (Achillea), columbines (Aquilegia), chrysanthemums of various sorts, blanket flowers (Gaillardia), delphiniums, daylilies, peonies and clematis.
Small shrubs are appropriate, too. Consider junipers, pines, dogwoods and, where they are hardy, azaleas and rhododendrons.
The problem with shrubs more deeply rooted than these is that roots can enter the pipes and clog them. This could force the sewage system to back up, eventually necessitating the replacement of the field. Willows and poplars, with their active, moisture-seeking roots, could cause difficulties.
Trees should be grown no closer to the septic system than their mature height. That is, a tree that could grow 12 metres (40 feet) tall should be planted at least 12 metres away.
Avoid construction, rock gardening and heavy garden ornaments over the septic field, and don't dig deeply for any reason, including when planting or tending. The drainage pipes are usually 1.3 metres to 1.8 metres (four to six feet) apart, and not more than 30 centimetres (12 inches) below the surface.
Vegetables can be grown on septic fields. Since the soil could be contaminated with runoff from the septic tank, avoid root and leafy vegetables that could be splashed or exposed to the soil. Plant roots will not absorb human disease organisms, but the soil itself could be contaminated. Better choices are tomatoes, peppers and beans. Mulch around the plants to reduce soil splashing.
With the right attitude and a little imagination, I hope my tile bed can become a garden of varied heights, colours and possibilities.
Jennifer Bennett welcomes feedback at firstname.lastname@example.org or via