Gardening Solutions for Heavy Clay Soils

What should a gardener do with soil that compacts easily and drains poorly? Find out here 

Gardening in clay soil can be a difficult task. I know because I have gardened in heavy clay soil before. Let’s skip the muscle pain talk and instead discuss how to handle clay soil so you can have fun in the garden.

Not sure if you have clay soil? First, determine your soil type, then move on to the solutions for gardening with clay soil below.

Basics of clay soil

Amendments. Gardening in clay soil is great exercise, but I’ve learned the hard way that some plants, like root vegetables, won’t grow well unless you significantly improve the soil. If you’re going to invest your effort and money into improving your clay soil, think strategically about where to do it. Raised vegetable garden beds or garden beds near your porch or backyard are great places to focus your fertilizer. The linear beds in this garden are nicely designed and easy to access, so you can add fertilization on a regular basis.

Sand and compost are the most important conditioners for clay soils. Adding well-graded sand (i.e., various particle sizes) to 50% of the soil will improve drainage, but is an expensive method. Compost and mulch work wonders on clay soil. You’ll want to make your own compost, as we add it to the clay at least once a year.

Understand what type of garden you can get from clay soil. For example, it would take a lot of work to turn clay soil into a garden of tender annual crops without doing a lot of amendments. Working with what you have will make you much happier in the long run. It is possible to improve soil to the point where new types of soil can be built on. This is a method many botanical gardens use to create special display gardens of drought-tolerant or wetland plants in areas without suitable soil types.

The meadow garden will also grow well in clay soil because it contains a variety of meadow-type plants that are clay tolerant.

Compaction. Clay soil compacts more easily than other soil types. Soil particles like to stick to each other. Walking or rolling a wheelbarrow over garden beds can compact the soil. When compression is complete, return to step one: re-cultivating the soil provides air and nutrients to the plant roots. 

Willow trees are tolerant of clay soils. The slender, thin leaves that are characteristic of this genus.

Wet soil. Never work when the garden soil is wet. If you work clay soil while wet(even tilling it slightly, the soil will eventually dry out into a rock-hard mass that is nearly impossible to break. Working clay soils while wet significantly disturbs soil ecology. Resist the urge to till the soil in early spring. Once the soil has completely thawed and opened up, it will have a cornbread-like texture and will make your time much easier.

Clay-tolerant plants

Many native plants can tolerate clay soil, but ask your nursery about your plant’s clay tolerance before testing it in your garden. Clay may slow the growth and spread of some plants, but true clay-tolerant species will thrive.

One of my favorites for Midwestern clay soils is the elegant Baptisia. The pretty blue flowers are from Baptisia australis, commonly known as false indigo or blue wild indigo. Because it has deep roots, it can withstand drought well and penetrates deep into the ground.

This spiky flower is the rattlesnake master. It is a funky plant with unstoppable vitality and vigor. Plant carefully. It is native to the American Midwest but can spread aggressively.

Additional clay-tolerant plants include redtwig dogwood, switchgrass and native serviceberry, linden and Viburnum spp.

Vines are underutilized in home environments and are a great way to add dimension to your garden without a lot of work. A sturdy kiwi vine on a top wooden pergola. It is hardy to produces edible fruit.

Garden planning

Plan your garden by organizing plants that fit together. Think of your garden like a plant
community where species interact to support each other and thrive.

For example, the magic of the tall grasslands of the Midwest is that plants grow with varying root depths. Roots can draw moisture and nutrients from different parts of the soil. What a clever plant! Armed with this knowledge, you can also mimic grassland conditions by planting several species with different root types together.

This lush shady garden features a variety of plant types with different root systems and is beautiful to look at.

Types of roots to look for

Primary root: A single, large main root that can grow very deep. According to the theory, the roots anchor the plant and help it survive drought. This is because the roots can draw water from deep in the soil. Primary root has one of the most resilient root systems and grows well in clay soil.

Fibrous roots: Numerous bundled roots that form thick clumps and spread in all directions.

Rhizome: A network of roots that sprout new plants from nodules along the root system. These plants, also called runners, can all form have connected colonies underground.

Planting plants with different root systems together will form plant colonies over time.