Clay soil is hard to work, but loaded with nutrients. Adjusting a low pH by adding lime helps make those nutrients more readily available for plants.
Adding organic matter in the form of leaves, hay, bark mulch, peat moss, and untreated grass clippings all help to make clay soil more workable.
You know you have clay soil when you can take a handful and can form clay figures.
Clay soil can be transformed in a loose, easy to work garden soil with time, patience, and persistence.
From California to Maine gardeners have to contend with clay soil. In some ways clay soil has gotten a bad rap. Yes, it does turn into bricks when dry, and when wet it’s probably best used for a facial, but it does have an upside. It holds water and nutrients well and as a horticultural friend of my says, "grows great grass". However, for any vegetable gardener, working with clay soil takes patience and perseverance. Many a gardener has slopped through wet clay, the heavy soil sticking to their boots and tools, or needed a pick axe to turn over cracked, dry clay. But if you are able to work your clay soil, you'll be rewarded with abundant crops.
Here are some tips on making clay soil your next best garden friend.
Test Your Clay – A key with any soil is to adjust the pH to the appropriate level for the crops you're growing. For vegetables, that would be between 6.5 and 7.0. Clay is loaded with nutrients, but if the pH is too low or high, they won't be available for your plants no matter what you do.
If you're gardening in the Southwest and a soil test calls for the addition of calcium, consider adding gypsum to your clay soil. Not only does it add calcium nutrients to your soil, gypsum helps break the bonds between clay particles and loosens the soil. However, don't add gypsum if not called for in your soil test. Chances are your soil already has abundant amounts of calcium and adding more will cause a nutrient imbalance.
Add Organic Matter – Whether it be clay or sandy soil, organic matter is the key to making your soil healthier and easier to work. It doesn't matter so much about the form of the organic matter as it does when you add it. Work in a 6- to 8-inch thick layer of coarse raw materials, such as chopped leaves, untreated grass clippings, hay, straw, peat moss or fresh manure in fall or a few months before you're going to plant your garden. It will take that long for the soil microbes to break down the high carbon material into humus that the plants can use. Only work the organic matter into the top 6- to 12- inches of soil. Add a 2- to 3-inch thick layer of finished compost or aged manure anytime time right up to planting. This works best on clay soil that has already been amended with raw materials so it's beginning to loosen up.
Another form of organic matter that helps immensely to make clay soil more workable is a cover crop. If you have the time and patience, grow a cover crop, such as clover, winter wheat, or buckwheat, in your garden area the year before you plan on planting. Tap-rooted cover crops, such as alfalfa and fava beans, are great at breaking up clay and pulling nutrients up to the top layers of soil from the subsoil. Growing cover crops that are tilled into the soil and replanted a few times during the growing season will add loads of organic matter and allow you to better work your garden once you get started.
Grow Up – Some gardeners contend with clay soil by avoiding it. If you have a small garden, it might be easier to build raised beds on top of your clay soil and fill the beds with a mix of loam and compost. You're basically creating a container on top of the soil, where you'll be better able to successfully plant your crops right away. Not only will the soil be easier to work with, because it's in a raised bed, you won't be stepping on the soil and compacting it.
The Miracle of Mulch – One of the biggest problems with clay soil is it easily compacts. To keep it from getting too dense and to prevent the soil from cracking and drying out, add a 2- to 3-inch thick layer of organic mulch over the soil during the growing season and replenish it as needed. The organic matter provides a carpet so you won't be packing down the soil as much when walking on it, and as the organic matter breaks down, it's helping loosen the clay. If you aren't growing a winter cover crop, consider covering the garden with organic matter (leaves, grass clippings, hay) all winter so the winter rains and snow don't compact the clay soil further.