Question about planting ornamental grasses over a septic system

Q. I have a septic system that I would like to plant ornamental grasses over. This is located on a slope of about 30 degrees. The soil is mostly clay. The area receives 4-5 hours of sun per day. I'm located in north Georgia. I enjoyed your article in Nov./Dec. of Georgia Gardening. Any information or resource you might provide would be appreciated.

By SuSanA Secretariat - Septic tank Uploaded by Elitre, CC BY 2.0

A. Planting grasses over your septic system is a good idea. If septic repairs are needed, grasses will recover more quickly than shrubs.

If planting over the drain field, I suggest you plant shorter grasses because root systems tend to be commensurate with top growth. Tall grasses like Cortaderia, many Miscanthus and Panicum species have deeper roots, which you should avoid. If planting over the septic tank itself, you could theoretically plant taller Miscanthus, Panicum, Agrostis, etc., because the concrete septic lid would prevent root penetration. But septic tanks usually are not buried deeply, so tall species might not have enough soil to grow anyway.

You should also consider whether you want full coverage of the area such as a lawn substitute, or clumping grasses which tend not to grow together. If you want clumping grasses, some good ones include Festuca ovina var. glauca, Helictotrichon sempervirens, Muhlenbergia capillaris var. filipes, some dwarf cultivars of Pennisetum alopecuroides 'Little Honey', 'Burgundy Bunny', 'Little Bunny', Carex hachijoensis (syn. Carex morrowii). You could also use grass-like plants such as Liriope muscari 'Aztec', Liriope muscari 'Variegata', L. muscari 'Densiflora'

If you want creeping grasses, some good ones include Carex pensylvanica, Festuca rubra,  Hakonechloa macra, or grass-like plants such as Liriope muscari 'Royal Purple', Liriope spicata, Ophiopogon japonicus.

I've not provided an exhaustive list.

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