Soil is considered to be clay when its particles are very fine and when wet the clay soil feels a bit sticky. Just because a soil is clay does not mean it will not drain well. Clay that is brown in color has a lot of iron in it and will drain pretty well. It is the gray clay that tends to drain slowly.
In either case, the goal is to get soil microbes and earthworms to begin making the clay particles larger by gluing little particles together. The larger particles allow for larger air spaces to be created, improving the drainage as well as making it easier for a plants roots to move through the clay soil. Earthworms and soil microbes need organic materials to eat so they can multiply and begin turning your clay into a nice black loam.
The long term solution to having a clay soil that is hard to dig and that drains poorly is to add organic materials year after year after year. In 3 to 5 years, your “clay” problem will have disappeared.
Short Term Strategy For Clay Soil
Starting New - When preparing a clay soil for a brand new lawn or garden bed, it is very important that you add as much organic material as you can. This is the best time to get that organic stuff down into the soil 4 to 6 inches.
Planting Trees & Shrubs - In the section on Planting Trees and the section on Planting Shrubs we emphasize the importance of digging a saucer shaped planting hole rather than one with vertical sides like a cylinder. This advice is particularly important when planting trees and shrubs in a clay soil. In this case you should not amend the soil that you use to fill the hole after planting.
Planting Individual Flowers and Vegetables - When plant perennials, annuals, and veggies in a clay soil, we will add some shredded pine bark and a product called “Profile” to the hole and to any soil we use to fill the hole. We do this assuming that we will be amending the soil with organic mulch and using soil health products regularly.