What Are the Characteristics of Clay Soil?

A garden full of clay soil is a challenge, but if you work with it the right way, it will yield great results. Clay soil is high in nutrients, and it holds water well. The key is to unlock the nutrients and improve drainage. The key characteristic of clay soil is the small particle size, typically 0.002 millimeters in diameter or smaller.

A significant benefit is the high nutrient content in clay soil. The fine structure of clay soil holds nutrients that get trapped in between the particles. Clay soil also holds water well -- sometimes too well -- and it provides a stable base for roots to get a firm hold.

On the downside, clay soil gets wet and waterlogged easily, and when it dries out, it dries out hard and cracks. Water then may run into cracks that form, instead of moistening the soil and reaching the plant roots. The dense structure and high water content can suffocate roots and render the nutrients inaccessible to plants. Clay soil will compact easily if overworked.

Take a handful of soil and work it into a ball. Clay soil is malleable, meaning you can work it into shapes without it breaking apart or crumbling. Clay soil also has a sticky or tacky feeling when damp.

Adding bulky organic material to clay soil helps separate the fine particles. This improves drainage, helps unlock nutrients and helps keep the soil from compressing or drying out into a hard sheet.

Add bulky organic matter to the soil in the fall before the ground freezes or in the spring two to three weeks before planting.

Use a 6- to 8-inch-deep layer of:

shredded leaves

leaf mold

sawdust

peat moss

Use a 2- to 3-inch-deep layer of fine materials like:

plant-based compost

seasoned manure

Work the organic material into the top 6 to 12 inches of the soil. Turn the soil and break up clumps of clay and dirt as you go. The key is to blend the organic material thoroughly.

Working clay soil when it is too wet will compact the particles, further damaging the already compromised soil structure. If the soil is sticky, or if clumps stick to your tools, wait a few weeks until it dries out a bit before amending, digging or painting.

In dry weather, when clay soil is prone to drying out and cracking, use mulch 2 to 3 inches deep over the bed to keep moisture from evaporating. An organic mulch, like compost, leaf mold or sawdust, works well. Leave a 3- to 6-inch-diameter space around each plant so you don't suffocate the stems with the mulch.

One of the best ways to make good use of clay soil is by selecting plants that grow well in the clay conditions.

A few to try include:

Chinese Juniper (Juniperus chinensis), an evergreen shrub that grows in U.S. Department of Agriculture plant hardiness zones 4 through 9. In USDA zones 2 through 6, common Juniper (Juniperus communis) grows well. 

Bulbs such as crocus (Crocus vernus), hardy in USDA zones 3 through 8, and snowdrops (Galanthus

nivalis), hardy in USDA zones 3 through 7 are good choices for clay soil areas.

For a lush foliage look, grow ostrich fern (Matteuccia struthiopteris), hardy in USDA zones 3 through 7. 

In warm climates, you can grow the cold-sensitive canna lily (_Canna x generalis_), a flowering perennial that thrives in USDA hardiness zones 8b through 10b. 

For a little color, try the blue-flowering aromatic aster(Symphyotrichum oblongifolium), hardy in USDA zones 3 through 8, or the yellow-flowering willow-leaved sunflower (Helianthus salicifolius), hardy in USDA zones 4 through 9.