Planting in clay soil is great for the vegetation that have roots strong enough to break through the hardened ground and compacted clay. Amending an area to make suitable for gardening other types of vegetation is doable. The main idea to remember is to amend an entire area NOT just a single hole for the desired plant to root.
Why is it important to improve the soil structure in an entire area rather a single location? If a gardener focuses on a single location once the plant roots it will grow root length only as far and wide as the hole that was amended. Once the roots reach the soil that is clay the roots will grow inward as they are unable to penetrate through the unforgiving clay soil. The plant may survive, but it will be severely root bound.
Checking soil quality is very important, drainage of the soil is imperative. I also researched a multitude of opinions on the best practices of checking soil quality, and the one common factor each opinion offered is to check more than one or two locations in the ground. Some locations of your yard may require different types or amounts of amendments making it even more important to check the soil’s texture in multiple locations. Dig a hole one foot deep fill it with water wait for it to drain, refill to the top, and time how long it takes to empty.
Proper drainage of the soil helps plant growth. If the water drains to slowly you more than likely have clay, but if it drains to rapidly, It will not be able to retain water or plant nutrients for healthy plant growth. In soil where the water drainage is faster than cup and hour the soils may have too much sand. In cases of clay soil with poor drainage mixing builder’s sand or compost (annually) will improve soil quality.
Adding organic amendments to the soil lightens soil texture, discourages compacting clay, adds nutrients, improves drainage and aeration, and moderates soil temperature, and provides pore space. Amend clay soil with organic matter, decomposed organic matter, (if you can tell what it is it is not decomposed enough) by working the compost into the soil.
Using undecomposed organic matter such as wood chips or mulch are great for on top of the soil, but should not be worked into the clay soil during the growing season. the reason it is not suggested during growing season, the undecomposed matter will continue its decomposition and rob the soil of further nitrogen to aid in its process. Sometimes it is referred to as a work in progress when using material that has not fully reach compost.
During the winter months its is fine to use the under decomposed material, the finishing touches of turning to compost will occur during the non growing season, I know there is always an exception to the rule.
The most important aspect to remind yourself, clay soil can be great soil if amendments are made. If you have questions about the pH levels in you soil don’t hesitate to contact your local County Extension Service and request a soil sample be taken.