Condensed over long periods of time, clay soils are old, tightly packed soils. They’re found all over the world, including in most parts of the U.S. One sure way to recognize clay soil is if water sits around after a rain, or if your soil is sticky.
A soil is considered clay when it contains 40 to 100 percent clay. The clay particles are tiny. They pack tightly, stick together and squeeze out the air channels plants and microbes need to survive.
The Benefits of Using Clay Soil
Once you understand the difficulty of working with it, clay soil’s density provides a stable environment with few surprises. Here are the benefits of using clay soil:
It holds water and nutrients:
During dry spells, clay can still offer plants moisture. Because of clay soil’s low presence of macro pores moisture moves through the profile quite slowly and nutrients have an incredible number of adsorption sites.
Sticky can be good for plants:
Clay particles are negatively charged, meaning they attract positively charged, beneficial minerals like potassium, calcium, ammonium and magnesium. Like a food bank, clay soils release ions as plants and microbes call for them.
It’s erosion resistant:
Dense and heavy also means immovable. Clay soil resists wind and water erosion that can deplete the mass and the nutrient density of lighter, more porous types of soils.
The Disadvantages of Clay Soil
Clay soil is difficult to work largely because it’s so dense and sticky.
Clay soils are really good at holding onto moisture, they can easily become waterlogged and stay far too wet for far too long during rainy weather or if too much supplemental water is added. The density and poor drainage can lead to some of these problems:
Drowned root systems:
clay soil has a disproportionate ratio of micro pores. These are small spaces that trap water — unlike macro pores, the larger gaps that allow moisture and air to move freely. With micro pores, it is easy to fill the profile with moisture and potentially drown root systems. Because roots need oxygen to breathe, plant health can be adversely affected quite quickly in poor conditions.
Heavy weight:
The density of clay soil is quite high, making it considerably heavier than other soils and harder to break apart or till through. If you’ve ever lifted a clump of wet, sticky clay, you can imagine how hard a whole plot of that might be to turn in a garden.
Impermeability:
When clay soil isn’t waterlogged and heavy, it’s hard as a rock. Clay tends to form solid layers that can become nearly impermeable to water, when compacted. In spring, dispersed clay forms a crusty layer on top of clay soils, making it difficult for seeds to sprout. When dry, clay soils can become so tightly packed they bend or break tools.
How to Make Clay Soil Better
One good thing about clay soil is that it can be improved upon. With patience and effort, you can change the profile of your clay soil and make it easier to work with and more likely to yield the results you desire. Here’s how to improve clay soil:
Break it up.
Cut through the dense profile of clay soil, slowly add decomposable, coarse organic matter, such as pine bark chips, and other, larger inorganic particles, such as coarse sand, can help break up the clay, keep the particles separated, and create more open pore space in the soil. Just make sure these are tilled into the soil so they become well-incorporated throughout the clay profile.
Try raised beds.
Gardening with raised beds will help drainage and avoid standing water on top of your plantings. Raised planting beds mean less foot traffic and compaction on clay soils and shifts the plant roots above the sitting water.
Top it off.
Sprinkle gypsum on the soil surface. It replaces sodium with plant-friendly calcium and makes the neutral clay soil more workable. Top-dress clay soils with a light layer of straw, fine bark or compost in the fall, to protect against surface crusting.
Dig down deep.
To help with drainage issues, dig through the clay layer into the soils below. This can help alleviate any drainage concerns by opening up the flow of water through the soil profile. If the density issue is severe, add calcined clay pellets along with the other amendments. They will eventually break down.
The Best Plants for Clay Soil
Petunia
Petunias have been popular for generations because they come in every color of the rainbow. Look for hybrid types that don’t require you to deadhead (remove spent blooms) to keep blooming until a hard frost.
Lantana
This shrubby plant with insanely bright colors is super-tough! It doesn’t mind heat or drought. It’s an annual in cold climates but are perennial in warm climates.
Bee Balm
As the name indicates, this perennial is a favorite of bees and many other pollinators. It comes in different shades of pinks and purples and blooms for weeks and weeks!
Potentilla
For low maintenance blooms all summer long, this shrub has a nice mounded shape that works well in mass plantings or mixed borders. It’s also extremely cold hardy.
Coneflower
Also known as echinacea, these flowers offer gorgeous, saturated colors from white to hot pink to deepest coral, making them a great addition to any garden. Bees and butterflies love this perennial.
Black Eyed Susan
This smiley-faced perennial is a must-have because it blooms for months starting in mid-summer through fall. It doesn’t mind heat or cold, so it’s a versatile plant in many different planting zones.
Bearded Iris
With thousands of varieties, this incredible perennial comes in every color of the rainbow! They’re tolerant of many soil types, multiply readily so you can transplant elsewhere in your garden or share with friends, and are low-maintenance bloomers that flower from spring to early summer, depending on where you live. Bet you can’t plant just one type!
Daylily
Daylilies are the ultimate in low-maintenance perennials. Although each flower blooms for just one day (thus, the name!), multiple flowers appear on each stem. They come in an astonishing array of sizes and colors with single, double, or frilly petals.
Lilac
Lilac is an old-fashioned shrub with pretty, fragrant pink or purple spikes in mid-spring. Look for re-blooming types which flower again later in the season. New dwarf sizes fit tidily in small spaces.
Hosta
Hostas are reliable, unfussy perennials that come in every size and color you can imagine. They typically are considered shade lovers, but they actually like a little morning sun. Just be aware that deer love them!