The organic content is a critical key to healthy soil, whether it is sand or clay. Like clay, organic matter acts as glue, holding soil particles together that provide pore spaces needed for oxygen and water exchange. Organic matter added to the soil helps to hold moisture content in sandy soils and provide needed oxygen in clay soil. It also makes nutrients available for plant use.

Clay soils, with their minute particles, have very tiny pore spaces that drain slowly. This can leave soils saturated with water, reducing space for oxygen. Since oxygen is a key element necessary for most growing plants, any soil with poor drainage can lead to damage or death of plant
life.

Amending your soil properly can overcome heavy, compacted clay and get it back on track for healthy garden growth. Adding materials such as organic compost, leaf mold, pine bark, composted leaves and gypsum to heavy clay can improve its structure and help eliminate drainage and compaction problems.

You can buy compost in bags, and that's fine for a small garden or for container gardening, but it is also available in bulk which is  less expensive. In bulk it is sold by the cubic yard (3ft x 3ft x 3ft) and often available by either pick-up or delivered.

Probably the least expensive compost is shredded leaves. If you have lots of trees, that's a fairly easy material to accumulate; however, you would need to own or rent a shredder. Shredded leaves will deteriorate over the winter and need to be applied annually.

Other organic materials include well-composted animal manure (available in bags or at some local farmers--but be sure it's aged), weed-free grass clippings and organic mulches such as shredded bark. Rabbit manure is especially good as it does not burn plants.

Unfortunately, there is no cost-free material available to improve your soil. A soil test from Michigan State University Extension
for a home garden will provide a measure of the organic content of your soil as well as information on soil type, nutrients, soil pH and recommendations to improve the soil. An annual application of compost, leaf mold and other material may be recommended to maintain ideal levels of organic matter that is slowly depleted each year by micro-organisms. If the soil has less than 3 percent organic matter, additions of 3 cubic yards of organic amendment per 1,000 square feet will help keep levels stable in the soil.

Self-mailer soil test kits from the Michigan State University Plant and Pest Diagnostic Lab are available. You can obtain them at the link below. Full instructions are there and also come with the kits. The cost is $25. The Lab will make recommendations for any needed soil amendments.

https://shop.msu.edu/product_p/bulletin-e3154.htm