Improve Clay Soil: Gardeners Share Their Top Tips

Clay soil is found in many American gardens, but it isn't a hospitable home for all plants. If you're preparing your garden for summer, or want to grow flowers or vegetables, you might struggle.

There are ways to make it a friendlier environment for beautiful blooms or tasty produce, though. Below, two experienced gardeners share their secrets for transforming clay soil, with just a day of work and a whole lot of organic matter.

What Is Clay Soil?

Clay soil is made of fine mineral particles and not much organic material. It's a heavier earth that tends to stick together and, since there's no space between the particles, the soil does not drain.

"If you have noticed that water tends to puddle on the ground rather than soak in, it is likely your soil is clay," according to Donald Loggins, the last original gardener at the first community garden in New York City, Liz Christy Community Garden.

Soil that consists of more than 50 percent clay particles is referred to as "heavy clay," Loggins told Newsweek. You can identify it because it sticks to your shoes and garden tools like glue, forms big clods that aren't easy to separate, and crusts over and cracks in dry weather.

The ideal soil for gardening is loamy—a mix of sand, clay, intermediate mineral particles and organic materials. It will drain well and have good nutrient retention.

Advantages and Disadvantages of Clay Soil

Amber Scott Freda, a garden designer based in New York, told Newsweek that because clay soil retains moisture for longer, it can prevent plants from drying out.

Plants such as evergreens tend to grow well in this type of earth, she said, while species from more arid climates such as succulents, rosemary and lavender are used to growing in lighter soil and will dislike being wet for so long.

"Vegetables and annuals dislike clay soil because it's hard for their small roots to grow in such dense soil," she added.

Loggins said: "Clay soil is prevalent in many parts of the United States, and it can be very problematic if you are trying to grow a flower or vegetable garden." In clay soil, vegetable roots struggle to force their way through and spring flower bulbs tend to rot over the winter.

soil with sprouting seeds.
Soil with sprouting seeds. Vegetables struggle to grow in clay soil because their roots can't break through the dense material while spring flower bulbs tend to rot in the wet winter. Getty Images

How to Improve Clay Soil

Improving your soil will take a bit of work, Loggins warned. Most of the job only has to be done once, but some annual upkeep is necessary.

You have to add a good dose of organic matter to the soil and let nature do its work. According to Freda, you can mix clay soil with gypsum, compost or pine bark to make it lighter and better aerated.

You can also lay several inches of mulch on top of clay soil and leave it to break down gradually and improve the soil. "Leaves are nature's best mulch, so if you can resist removing the leaves from your garden beds each year, they will gradually break down and improve the soil naturally," she added.

It is best to tackle an entire bed at once, rather than just individual planting holes as you need them, Loggins said.

"If you dig a planting hole in clay soil, then drop in a plant and nicely amend only the soil you're using to backfill, your plant will be happy for a little while. But you have done nothing more than create an in-ground flowerpot.

"Eventually, the plant will start sending out roots that will be stopped in their tracks when they reach the clay walls of the planting hole. You'll end up with a root-bound plant that won't grow as large or as healthy as it should."

Loggins recommends adding 6 to 8 inches of organic matter to the entire bed. This can be grass clippings (as long as they haven't been treated with chemicals), shredded leaves, rotted manure or compost.

After you've spread your organic matter, mix it into the top 6 to 12 inches of soil using a shovel—or a tiller "if digging is just too hard on your back."Your garden will look several inches higher than it was, but the beds will settle as the organic material breaks down.

How to Break Up Clay Soil Quickly

Break up the soil with a hoe or spading fork 5 to 6 inches into the ground. You can use a tiller if strictly necessary, but be aware that this type of motorized tool can kill worms and other organisms that are vital for the soil.

If the clay is particularly hard, it may help to spread a small layer of sand across it before adding the organic matter.

How to Improve Clay Soil Drainage

Adding compost will improve drainage. Loggins said you should do this when the soil is dry, because working in wet clay is messy and will compact the bed even further.

Compost "not only helps with the soil structure," he explained, but the glomalin compound created by the mycorrhizal fungi in compost "binds the small clay particles together into aggregates with a waxy coating, thus creating more space between them for air and water to flow."

Preparing Clay Soil for Vegetable Gardening

If you want to grow vegetables, it's best to work the organic matter deep into the soil—because the roots will end up there—and to do this before planting.

"You can till as deep as a tiller will go, or dig sections of a bed at a time to a foot deep, work in compost, then replace the soil and do the next section. In future years, just work the surface, as organic matter you've worked in deeply will decompose quickly when brought up to the surface," Loggins said.

You can also increase organic matter in clay soils by planting cover crops. "These are crops planted as you prepare beds, for a season or year prior, or in fallow periods between annual crops such as flowers and vegetables. They consist of small grains and grasses such as buckwheat, ryegrass and oats," he said.

Legumes such as clover can benefit the soil by "fixing" nitrogen from the air for its use.

How to Take Good Care of Soil

Freda believes the key to a beautiful, healthy garden is treating your soil with compost. "It's what nature has been doing since the beginning of time, and Mother Nature always knows best."

Her simple advice is to "add several inches of compost to clay soil each year and mix it in well with the existing soil until the soil measurably improves."

Man handling soil
Man handling soil. The best way to improve a sticky, dense clay soil is to mix organic matter with it and let nature do its work. Getty Images