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Sandy's Garden

Planting on a Slope

Hillsides are the hardest to landscape

By: Sandy Feather ©2011
Penn State Extension


Q. I have a hillside to plant and do not want to work up the soil up for fear of erosion. I know that the soil is heavy clay. Can you recommend plants that will perform well in clay without amending it with organic matter? It is a big area, so I am not afraid of large plants.
  
  A. There are many plants that will be fine in such a situation. Shrubs and small trees that spread by suckering (sending up shoots from their root systems) such as some species of red-twig dogwood, sumac and bottlebrush buckeye are excellent for holding hillsides in place. Of course, you should still have a soil test performed so that you know the pH (acidity or alkalinity) and fertility level of the soil. Also make sure that the site drains reasonably well. Do not assume that it does just because it is a hillside.

Drainage Test

Dig a number of holes (how many depend on the area of the site - you want a representative sample) 15 - 24 inches deep and fill them with water. If they drain in a few hours, the drainage is fine. If not, drainage could be a problem. In that case, you may need to install French drains or limit your selection to plants that tolerate poor drainage. Those plants that tolerate moist soil are marked with an * in the following list.

You do not mention whether the site is sunny or shady, so the following list includes plants for both situations. After the list I have included a bibliography of suggested references so that you can read more about these plants before making your final selections.

Plants that perform well in clay soil include:

TREES

Red Maple* (Acer rubrum)

Horsechestnut  (Aesculus spp.)

Serviceberry* (Amelanchier spp.)

Hornbeam (Carpinus spp.)

Hackberry* (Celtis occidentalis)

Fringetree* (Chionanthus virginicus)

Fringetree
Fringetree

Hawthorn (Crataegus spp.)

Gingko (Gingko biloba)

Larch (Larix spp.)

Goldenrain Tree (Koelreuteria paniculata)

Crabapple (Malus spp. and cultivars)

White Pine (Pinus strobus)

Flowering Cherries (Prunus spp. & cultivars)

Black Gum* (Nyssa sylvatica)

Hophornbeam (Ostrya virginiana)

Amur Corktree Phellodendron amurense

White Spruce

Pin Oak* (Quercus palustris)

Pin Oak
Pin Oaks need room to grow

Scholar-tree  (Styphnolobium japonicum)

Arborvitae (Thuja spp.)

Linden (Tilia spp.)

Japanese Zelkova (Zelkova serrata)

 

SHRUBS

Bottlebrush Buckeye (Aesculus parviflora)

Chokeberry* (Aronia spp.)

Flowering Quince (Chaenomeles spp.)

Summersweet* (Clethra alnifolia)

Red & Yellow Twig Dogwood* (Cornus alba, C. sericea)

Grey Dogwood* (Cornus racemosa)

Smokebush (Cotinus coggygria)

Forsythia (Forsythia x intermedia)

Witch Hazel* (Hamamelis spp.)

Rose-of-Sharon (Hibiscus syriacus)

Hydrangea (Hydrangea spp.)

Tardiva Hydrangea
Hydrangea paniculata 'Tardiva'

St. Johnswort (Hypericum spp.)

Japanese Holly (Ilex crenata)

Inkberry Holly* (Ilex glabra)

Winterberry* (Ilex verticillata, Ilex serrata)

Juniper  (Juniperus spp. & cultivars)

Japanese Kerria (Kerria japonica) 

Bayberry* (Myrica pensylvanica)

Mockorange (Philadelphus spp.)

Purpleleaf Sand Cherry (Prunus x cistena)

'Gro-low' Fragrant Sumac (Rhus aromatica 'Gro-low')

Staghorn Sumac (Rhus typhina)

Saltspray Rose (Rosa rugosa)

Dwarf Blue Arctic Willow* (Salix purpurea ‘Nana’)

Elderberry* (Sambucus canadensis)

Common Lilac (Syringa vulgaris)

Bumald Spirea (Spirea x bumalda)

Vanhoutte Spirea (Spirea x vanhouttei)

Bridal's Wreath Spirea
Vanhoutte (Bridal's Wreath) Spirea

‘Crispa’ Cutleaf Stephanandra (Stephanandra incisa ‘Crispa’)

Snowberry/Coralberry* (Symphoricarpos spp.)

English Yew (Taxus baccata  ‘Repandens’)

Japanese Yew (Taxus cuspidata)

Anglojap Yew (Taxus x media)

Arborvitae (Thuja spp.)

European Cranberrybush Viburnum* (Viburnum opulus)

Doublefile Viburnum (Viburnum plicatum var. tomentosum)

Blackhaw Viburnum* (Viburnum prunifolium)

Sargent Viburnum* (Viburnum sargentii)

American Cranberrybush Viburnum* (Viburnum opulus var. americanum)

Weigela (Weigela florida)

Yucca (Yucca filamentosa)

 

GRASSES, PERENNIALS AND BULBS

Blue Star (Amsonia tabernaemontana)

Big Bluestem* (Andropogon gerardii)

Swamp Milkweed* (Asclepias incarnata)

Asters* (Symphotrichum spp.)

False Indigo (Baptisia australis)

Bergenia* (Bergenia spp.)

Foxglove* (Digitalis purpurea)

Purple Coneflower (Echinacea purpurea)

Coneflower
Coneflower

Ravenna Grass (Erianthus ravennae)

Joe Pye Weed (Eupatorium purpureum)  

Bigroot Geranium (Geranium macrorrhizum)

Sneezeweed (Helenium autumnale)

Daylilies* (Hemerocallis hybrids)

Hostas* (Hosta cultivars)

Siberian Iris* (Iris siberica)

Beebalm* (Monarda didyma)

Daffodils (Narcissus spp. and hybrids)

Narcissus
Daffodils

Switch Grass* (Panicum virgatum)

Oriental Poppy (Papaver orientale)

Obedient Plant* (Physostegia virginiana)

Rodgersia (Rodgersia spp.)

Brown-eyed Susan (Rudbeckia spp.)

Sedum (Sedum spp.)

Goldenrod (Solidago rugosa)

Indian Grass (Sorghastrum nutans)


BIBLIOGRAPHY

Armitage, Allan M., Herbaceous Perennial Plants, Stipes Publishing, 2008. (ISBN 9781588747754)

Darke, Rick, The Color Encyclopedia of Ornamental Grasses, Timber Press, 1999. (ISBN 0881924644)

Dirr, Michael A., Manual of Woody Landscape Plants, Stipes Publishing Co., 2009. (ISBN 1588748685)

DiSabato-Aust, The Well-Designed Mixed Garden, Timber Press, 2003. (ISBN 0881925594)

Gerhold, Henry D., et. al., Landscape Tree Factsheets, Penn State University, 2001. (ISBN 1883956014)

Still, Steven M, Manual of Herbaceous Ornamental Plants, Stipes Publishing Co., 1994. (ISBN 0875634338)


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