Q. I have a small sunny hillside next to my driveway. It is hard to mow and I would like to replace the grass with a ground cover plant like periwinkle. How do I get rid of the grass without eroding the hillside? I tried this before on the other side of the driveway, and we ended up with dirt in the driveway every time it rained. I would like to avoid terracing it if possible.

A. You can kill the grass with a nonselective herbicide such as Roundup (or one of the many knock-offs available since Monsanto's patent on glyphosate expired), but leave the dead grass in place. Do not mow it beforehand, because more leaf surface allows for better absorption of the herbicide, resulting in better control. It will take 10-14 days for Roundup to kill the grass, including the roots.

Once the grass is dead, mow it so that it is shorter, and then simply plant your ground cover right in the dead grass. The dead grass will act as a mulch and hold things in place until the ground cover fills in and takes over. Now is a good time to spray and even plant the site, depending on what you choose to replace the grass.

You can apply a thin layer of bark mulch over the dead grass once the area is planted for a neater appearance. An inch or two is sufficient.

You should still have a soil test performed so that you know the pH (acidity or alkalinity) and fertility level of the soil, which will aid in proper plant selection. Soil test kits are available from your local Penn State Extension office for a nominal fee (details below).

Since you have a sunny hillside, periwinkle (Vinca minor) is not the best choice; it prefers some shade, especially from the hot afternoon sun. Also, since you are not incorporating organic matter or preparing the soil to any degree, it is important to choose tough plants that do not mind less-than-ideal soil conditions.

Although you certainly do not want anything tall that would block your line of sight pulling out of the driveway, ground cover plants do not have to hug the ground. Many perennial flowers can act as a ground cover, with the added bonus of flowers through the growing season.

Here is a list of good ground covers for your spot. Evergreen and semi-evergreen plants are marked with an . Although these are tough plants, they will not tolerate poorly drained soil. After the list I have included a bibliography of suggested references.

• Blue fescue (Festuca ovina glauca)
• Daylilies (Hemerocallis spp.) especially smaller re-blooming varieties such as 'Happy Returns' or 'Rosy Returns'
• Cheddar pinks (Dianthus gratianopolitanus) especially 'Firewitch' or 'Bath's Pink'
• 'Nikko' slender deutzia (Deutzia gracilis)
• Ground cover junipers (Juniperus horizontalis, J. procumbens 'Nana')
• Lily turf (Liriope muscari)
• Creeping phlox (Phlox subulata)
• 'Gro-low' fragrant sumac (Rhus aromatica)
• 'Green Mound' Alpine currant (Ribes alpinum)
• Sedum (Sedum spp.) especially 'Vera Jamison' (Sedum spurium) and 'Angelina' (Sedum repestre)
• Japanese spirea (Spirea japonica 'Little Princess' or 'Magic Carpet')
• 'Crispa' cutleaf Stephanandra (Stephanandra incisa)
• Spreading English yew (Taxus baccata 'Repandens')

Bibliography

• "Armitage's Garden Perennials" by Allen M. Armitage, Timber Press.
• "Perennials for American Gardens" by Ruth Clausen and Nicolas Ekstrom, Random House.
• "The Color Encyclopedia of Ornamental Grasses" by Rick Darke, Timber Press.
• "Taylor's Guide to Ground Covers" by David C. Michener and Nan Sinton, Houghton Mifflin.
• "Taylor's Guide to Shrubs" by Kathleen Fisher, Houghton Mifflin.
• "Manual of Woody Landscape Plants" by Michael A. Dirr, Stipes Publishing.

In Allegheny County, consumer soil test kits cost $12 each, and come with detailed instructions. Customers ordering multiple kits at one time pay $9 each for additional kits. Send a check made payable to Penn State Extension to 400 N. Lexington St. Pittsburgh, Pa. 15208. Write Attn. Soil Test Kit in the lower left corner of the envelope.