Battling the Bathtub Effect
I recently renovated my courtyard, carefully double-digging the clay soil and adding plenty of organic matter. When heavy spring rains arrived, I discovered I had created a giant bathtub. As deep as I had dug, and despite a slight slope to the garden, I could not change the fact that my garden had solid clay subsoil, which prevented excess water from leaving the area.
When it comes to drainage, clay soil can be incredibly problematic. Luckily, there are a variety of solutions for improving drainage in heavy clay soil. I used a French drain to solve my drainage problem. A French drain is a small trench fitted with a perforated pipe and filled with gravel to carry water downhill to an outlet point.
For a French drain to work properly, it must be installed so that it drops away from the area needing drainage. In the case of my courtyard, I installed the French drain along the lower edge of the garden and directed the pipe down our sloped lawn to an outlet point. Many gardeners also like to build a rain garden at the end of the drainage pipe, which is a wonderful way to capture the excess water.
Digging Dry Creeks and Building Berms
Sometimes, water can be directed and moved on the surface using a dry creek bed. As the name suggests, a dry creek bed is a stone bed mimicking a creek running through the landscape. Dry creek beds have several applications – they are used to move water away from an area where it collects and pools, or to slow the flow of water that runs down a slope, reducing erosion problems. You can also use a dry creek bed to move water from a gutter downspout toward a more desirable location in the landscape.
Dry creek beds provide a tough substrate for water to wash through and they add a decorative element to the landscape. Often installed in a serpentine manner, a dry creek bed incorporates plantings to soften the form and is connected to the larger landscape through carefully placed stone and selective hardscape materials.
Not all solutions need be so drastic or involved. Sometimes, simply amending the soil with organic matter loosens soil structure and improves water movement enough to solve drainage problems. Organic matter also invites beneficial organisms into the soil. Many insects and earthworms help aerate the soil through their movement and feeding, further enhancing water infiltration.
Likewise, deep-rooted cover crops such as daikon radish (Raphanus sativus) can help break through compacted clay soil, creating channels for root growth and water movement. Alternately, gardeners can build berms in the landscape to lift plants out of poor-draining clay. Use a loose, organic-rich soil when building berms to enhance drainage.
Working with What You’ve Got
When problem areas are located at low points in the landscape, added drainage is often not an option. In this case, it’s best to work with what you have. You can reduce some of the water problems through careful irrigation management and soil amendment, but that’s only part of the solution.
Selecting plants that tolerate wet soil will ensure that the low spots in your landscape perform to the best of their ability. Trees such as river birch (Betula nigra) and bald cypress (Taxodium distichum), water-loving shrubs like buttonbush (Cephalanthus occidentalis), and marginal plants such as cardinal flower (Lobelia cardinalis) and swamp milkweed (Asclepias incarnata) provide year-long beauty in poorly drained soil.
Improving Clay Soil Step-by-Step
Regardless of your drainage situation, improving the underlying clay soil is key to a thriving garden. Here’s a step-by-step guide to conquering clay soil:
1. Aerate the Soil
Injecting air pockets into clay soil is essential for improving drainage, breaking up compaction, and inviting in soil microorganisms. Use a digging fork, aeration tool, or even let clay-busting plants like daikon radish do the work for you.
2. Add Organic Matter
Incorporate lots of organic matter, like compost, leaf mold, and composted manures, to improve soil structure and nutrient content. This attracts microorganisms that further break down the clay particles.
3. Plant Cover Crops
Cover crops like clovers, vetch, and favas help incorporate soil amendments deeper into the clay, reduce erosion, and enrich the soil. Be sure to chop them back before planting your garden.
4. Mulch Appropriately
Protect your hard work by mulching with shredded leaves, straw, or alfalfa hay. This prevents compaction and retains moisture, all while feeding the soil as it decomposes.
5. Avoid Compaction
Create narrow, 3-foot-wide garden beds so you don’t have to walk on your precious soil. And be mindful of when you work the soil – only when it’s moist, never when it’s waterlogged.
Following these steps, even the heaviest, most stubborn clay can be transformed into a rich, loamy paradise. It may take some time and effort, but the rewards of a thriving, productive garden are well worth it.
As you can see, there are many creative solutions for improving drainage and conquering clay soil. By incorporating organic matter, aerating the soil, and choosing the right plants, you can turn that muddy mess into a lush, healthy garden.
Ready to start your journey to soil success? Head over to todaysgardens.org to learn more about our garden design and landscaping services. We’re here to help you conquer your clay and create the garden of your dreams.