5 Ways to Improve Clay Soil in the Garden

Photo: Luis Diaz Devesa/Getty Images

When you see standing water in your garden in the spring, but the same area transforms into a web of cracks in the summer, you have clay soil. There are several ways to improve clay soil in the flower garden, but as they say, when you have lemons, make lemonade: you should also plant flowers that are tolerant of heavy soils.

Do You Have Clay Soil?

Clay soil is made of fine particles that cause it to stick together, preventing normal drainage processes that keep plant roots healthy. If a gardener squeezes moist clay soil into a ball, the soil will retain that shape. Gardeners who regularly fight chicory, sorrel, and buttercup weeds are probably dealing with the clay soil that attracts these weeds.

Amend the Soil

Some gardeners make the mistake of adding sand to clay soil, thinking that adding matter from the opposite soil type will moderate the problem. However, sand and clay make a soil more akin to concrete than the rich loam all gardeners desire. The best soil conditioner for clay is organic matter, and lots of it. Gardeners should add organic compost, leaf mold, and green manures from cover crops to improve soil structure and tilth.

Garden centers commonly sell gypsum as a soil amendment for clay conditions. However, unlike organic matter, gypsum does nothing to improve the fertility of soil. Furthermore, according to the Puyallup Research and Extension Center at Washington State University, gypsum negatively affects the mycorrhizae that enhance root health and development.

Try Double Digging

Double digging is highly laborious, but it can be an effective way to remedy extremely heavy soils in small areas. The double digging method involves digging a 2-foot deep trench in the garden, filling it with a compost and soil mixture, and then returning the native soil to the trench and mixing it together.

Install Raised Beds

Creating raised beds is an easy way to subvert many soil problems, whether sandy or clay-based. Gardeners can choose the type of raised beds they want, exploring lasagna gardening options, raised garden bed kits made of composite or wood, or even hay bale gardening for the back of the flower border. Raised beds have the added bonus of warming up quickly in the spring, for earlier planting.

Prevent Soil Compaction

Clay soil is naturally dense and tends to waterlog easily, and these characteristics become exaggerated in the spring. Gardeners must take care not to walk on clay soil or work it with a tiller when it’s cold and waterlogged, or it will become nearly impervious to water and oxygen. Work clay soil gently with a pitchfork when it’s as moist as a wrung-out sponge, as this garden tool maintains the integrity of the soil strata.

Choose Plants for Clay Soil

Plants that thrive in clay soil are those that can cope with the extremes of sogginess and dry cracked earth that clay can bring.

Note from Esther: Most gardeners in Knysna have heavy clay to contend with.  Choosing the right plants can be a problem.  Below some plants that are suitable and recommended.

Shrubs and groundcovers:

Carissa macrocarpa (Large Num-Num)

Plumbago auriculata (Cape Leadwort)

Aloe ferox (Bitter Aloe)

Budeleja salvifolia (Sagewood)

Salvia chamelaeagnea (Blue Salvia)

Chlorophytum comosum vittatum (Hen and Chicks)

Gazania rigens (Trailing Gazanias)

Chlorophytum bowkeri

Dietes grandiflora


Buddleja saligna (False Olive)

Vachellia xanthophloea (Fever Tree)

Acokanthera oppositifolia (Bushmans Poison)

Diospyros lycioides

Ehretia rigida (Puzzle bush)

Grewia occidentalis (Cross-Berry)

Searsia species (Karee)

Reeds and Restio

Elegia tectorum (Cape Thatching Reed)