The Q&A Archives: Hard clay soil

Question: What are the best types of shrubs and flowers to plant in hard clay soil? What is the best way to
soften the soil? It is rock hard soil and very difficult to dig in.

Answer: The best thing you can do for a clay soil is to add composted organic matter, which will improve the structure and internal drainage and aeration of the soil. Do this any time you plant or replant a garden bed. Add a couple of inches of compost and work it in deeply. You might also consider building raised planting beds which will not only make the soil easier to work but will also improve drainage.

Choosing plants to grow in clay soil takes some discretion. Certainly, plants that need a well drained soil are not going to be happy growing in clay. Don't give up. There are plants that not only tolerate clay soil, many will also help break up and improve its texture. Rugged native prairie plants have the constitution to hold up in clay. Tap rooted plants can get deep enough so that their roots don't rot and they break up the texture of clay on their way down. Some plants that tolerate clay soils include the following:

Amsonia Blue Star (Zones 5-9)
Asclepias tuberosa Butterfly Weed (Zones 4-9)
Aster (various) Aster (Zones 4-8)
Coreopsis Tickseed (Zones 4-8)
Echinacea purpurea Coneflower (Zones 3-9)
Eryngium yuccifolium Sea Holly (Zones 5-10)
Helianthus angustifolius Swamp Sunflower (Zones 6-9)
Helianthus x laetiflorus False Sunflower (Zones 5-9)
Heliopsis helianthoides Ox Eye (Zones 4-9)
Hemerocallis Daylily (Zones 3-10)
Liatris pycnostachya Kansas Gayfeather (Zones 4-9)
Liatris spicata Blazing Star, Gayfeather (Zones 4-9)
Monarda fistulosa Wild Bee Balm (Zones 3-9)
Ratibida pinnata Drooping Coneflower (Zones 3-10)
Rudbeckia hirta Black-eyed Susan, Gloriosa Daisy (Zones 3-7)
Sedum 'Autumn Joy' (Zones 3-10)
Silphium integrifolium Prairie Dock (Zones 4-7)
Silphium laciniatum Compass Plant (Zones 5-9)
Silphium perfoliatum Cup Plant (Zones 5-9)
Solidago Goldenrod (zones 5-9)
Vernonia noveboracensis Ironweed (Zones 5-9)
Yucca filamentosa Adam's Needle (Zones 5-10)

Ornamental Grasses Suited for Clay Soils
Acorus gramiineus Grassy-leaved Sweet Flag (Zones 10-11)
Andropogon gerardi Big Bluestem (Zones 2-7)
Elymus canadensis Canadian Wild Rye (Zones 3-8)
Miscanthus sinensis Eulalia Grass (Zones 4-9)
Panicum virgatum Switch Grass (Zones 5-9)
Pennisetum (various) Fountain Grass (Zones 6-9)
Sorghastrum nutans Indian Grass, Wood Grass (Zones 5-8)
Spartina pectinata Prairie Cord Grass (Zones 4-7)

Shrubs for clay soils:

Amelanchier species Serviceberry hardy to zone 4
Aronia melanocarpa Chokeberry hardy to zone 3
Berberis koreana Korean barberry 4
Berberis thunbergii Green barberry 4
Caragana arborescens Siberian peashrub 3
Cephalanthus occidentalis Buttonbush 4
Cornus alba Tatarian dogwood 3
Cornus alternifolia Pagoda dogwood 4 Needs moist, acidic soils
Cornus racemosa Grey dogwood 3
Cornus sericea Red osier dogwood 3
Diervilla lonicera Dwarf bush-honeysuckle 3
Elaeagnus angustifolia Russian olive 2
Elaeagnus commutata Silverberry 2
Forsythia x 'Meadowlark' 'Meadowlark' forsythia 3
Forsythia x 'Northern Sun' 'Northern Sun' forsythia 3
Hamamelis virginiana Witch hazel 4
Ilex verticillata Winterberry 4
Juniperus species (most) Juniper 3
Lonicera species Honeysuckle 3-4 ?
Physocarpus opulifolius Common ninebark 2
Potentilla Fruticosa Potentilla 2
Rhamnus frangula Glossy buckthorn 4
Rhus species Sumac 2 Prefers well-drained soils
Ribes alpinum Alpine currant 2
Ribes odoratum Clove currant 2
Rosa rugosa Rugosa rose 2
Salix species Willow 2
Sambucus canadensis American elderberry 3
Sambucus pubens Scarlet elder 4
Spiraea species Spirea 3-4
Symphoricarpos albus White snowberry 3
Syringa species Lilac 2
Thuja occidentalis Arborvitae, white cedar 3
Viburnum dentatum Arrowwood viburnum 3 Prefers well-drained soils
Viburnum lentago Nannyberry viburnum 2
Viburnum opulus European cranberrybush

Best wishes with your landscape!

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