Last time we discussed how to grow and garden in sandy soil. This time, we’ll talk about clay soil.
From the soil facts, we know that clay soil has smaller particles compared to sandy and silty soils and it has good water retention qualities. The downside is the fact that clay soil could become:
- compacted and cloddy when you work with it while it’s waterlogged
- poorly aerated, because of the tight bonding of clay particles
- as hard as brick in extremely dry weather.
A highly compacted clay soil would need several years of TLC before it can be any good for growing.
Amending Clay Soil
Clay soil isn’t ideal gardening material but it’s fairly fertile. It can store important plant nutrients—a good foundation to build on when conditioning clay soil.
Your mission in preparing clay soil is in improving soil structure.
You’ll need to turn it into a looser, more crumbly or granular growing medium by mixing in large amounts of organic matter into clay soil. Organic matter stabilizes the aggregation of soil particles in the top soil, to reduce crusting, improve water handling and nutrient storage, and lessen erosion and runoff.
The good news is, once you’ve created a good soil structure, you won’t need to keep amending clay soil yearly as you would with sandy soil.
One material you can use is compost, integrated regularly and deeply into the soil.
“Green” composting materials that rot quickly (like young leaves) are best. “Brown” or slow-decaying materials like old straw, peat moss, shredded barks, or sawdust won’t be as practical. For one, “browns” don’t encourage aggregation as well as “greens”. For another, they also feed on the nitrogen that plants feed on so you’ll need additional inputs, too.
Organic fertilizers like blood meal, kelp extracts, cottonseed meal and fish emulsion would also improve clay soil structure.
Cover cropping with both leguminous and non-leguminous plants like hairy vetch, cereal rye, oats, and crimson clover would also be beneficial. Rather than leaving the garden uncultivated between crops or seasons, cover crops will also reduce soil erosion, improve water movement, stifle weed growth, prevent weed seed germination and discourage pathogenic nematodes from thriving in clay soil.
Gypsum, a rock powder with calcium sulfate, is a secret ingredient that gardeners add to their clayey garden beds. Gypsum loosens clay particles to improve soil structure, aeration and the flow of water deep into the soil. Every four or five years, 10 pounds of gypsum is worked into a hundred square foot of soil. Gypsum won’t be of much use with acidic soils. It only works best with alkaline or sodic soils so before treating your garden with gypsum, make sure your soil’s the right pH.
Here’s one more tip: humic acids also work wonders on clay soil as do inoculating plant roots with mycorrhizae, especially at the time of planting.
Watering Clay Soil
There are some seasonal considerations to keep in mind when watering clay soil:
- Because clay soil is water retentive, water within the soil could freeze up in winter and create humps that push the plants out.
- During summer’s hot, dry conditions, soil could turn so crusted that seedlings can’t emerge into the surface and their roots couldn’t burrow deeper into the soil.
- In spring, clay soil takes a long time to warm up so planting schedules might be delayed.
- The best time to dig or till is in autumn, when clay is at the right moisture level for handling.
Drip irrigation works best with clay soils. It allows you to deliver water at a very slow rate, giving it enough time to soak through to the root regions and drain away. In summer, a soaker hose trickling at a rate of a cup per minute could run across your garden beds for 1-3 weeks to distribute water evenly, avoiding bare spots.
Make sure that your plots and gardens have proper drainage. Consider growing your plants in raised beds if rainwater puddles don’t drain quickly.
Some gardeners advise mixing sand into the clay soil to improve drainage. It’s a dicey practice at best since the wrong size and texture when mixed with clay could turn your garden soil as hard as cement.
Tilling Clay Soil
Tilling is the initial critical step in soil preparation. It supports good structure for seedling growth and rooting, aeration, water regulation and oxygen distribution. When tilling, make sure that clay soil moisture is just right. “Just right” means moistened soil fractures, breaks or crumbles when pinched between your fingers.
A combination of air-drying, wetting, and raking will break up clods in moist clay to create a good soil structure.
Loosen clay soil with a garden fork before working with it. Puncture the soil and then gently wiggle the fork tines out. Turn over the soil, break the clods using the side of the fork, then leave the soil exposed to sun and air to dry. Once water has evaporated and the soil clods had crumbled, soften the clay again with a fine spray. Work the soil with a rake once it’s dried out.
Continued tilling can use up the organic matter in the soil as it encourages microbial life in the soil to consume the organic matter in large quantities. Once clay soil is friable and the plants are rooted deeply, you could consider switching to a minimum-till system. It will augment organic matter, carbon, total nitrogen and microbial life 2-4 inches from the soil surface.
Plants For Clay Soil
Growing plants that thrive in clay soil would ensure growing success. Here’s a list to give you some ideas:
- Trees: coffee, balsam fir, boxelder, blue beech, hawthorn, ginkgo biloba, butternut, apple, crabapple, pear, willow, oak, aspen, cottonwood, elm.
- Shrubs: lilac, honeysuckle, juniper, witch hazel, potentilla, Russian olive, burning bush.
- Flowers: aster, black-eyed susan, coreopsis, daylily, Japanese iris.
- Ornamental grasses: Canadian wild rye, switch grass, Indian grass, Fountain grass, prairie cord grass
That’s the lowdown on growing and gardening with clay soil. Next time, we’ll focus on silty soil.
How about you? Do you have tips and advice in preparing clay soil gardens? Share your story in the comments section below!