Clay soil is prevalent in many parts of the world. So, don't feel like you're all alone if that's what you have in your garden. And, if you do have clay soil, you know it can be a real pain to dig in and for plant roots to grow through. While many trees and shrubs grow well in clay, the roots of the majority of annuals, perennials, and vegetables just aren't strong enough to make their way through. Clay also tends to hold a lot of water, particularly in winter when there is less evaporation. This can cause problems for specific types of plants that don't like wet feet. During the warm season, and particularly when there is prolonged dry weather, clay soil can become as hard as a brick.
The good news is, with the addition of the right soil amendments and a little effort on the gardener's part, clay soil can be turned into a richer, more loose soil that flowers and vegetables will appreciate.
What is Clay Soil?
Clay soil is defined as soil that is composed of mostly clay particles. Soil that consists of over 50% clay particles is referred to as “heavy clay.” To determine whether you have clay soil or not, you can do a simple soil test. Most likely, you probably already know if you have clay soil. If your soil sticks to shoes and garden tools like glue, forms big clods that aren't easy to separate, and crusts over and cracks in dry weather, you have clay. Also, if you squeeze it in your hand, and it molds instead of falling apart when you open your hand, you probably have clay.
The Positives
Even clay soil has some good qualities:
- Retains moisture well
- Tends to be more nutrient-rich than other soil types. The reason for this is that the particles that make up clay soil are negatively charged. They attract and pick up positively charged particles, such as calcium, potassium, and magnesium.
The negatives
Clay has it's fair share of negatives as well. It is:
- Slow draining
- Slow to warm in the spring
- Compacts easily, making it difficult for plant roots to grow
- Tendency to heave in winter
- Tendency to be acid
Improving Clay Soil
Improving your clay soil will take a bit of work, but the good news is that the work you do will instantly improve the structure of your soil and make it easier to work with.
It is best to improve an entire planting area all at once, especially when you are planting ornamental plants such as shrubs and trees. After these have been planted, there's no going back to improve the soil further. In the vegetable garden, you can improve soil between each growing season.
When planting shrubs and trees, you can add organic matter, such as mushroom compost, composted cow manure or your own homemade compost to the soil to the backfill mixture. Or you can till or turn in organic matter to the entire planting area. If you will be just improving individual planting holes as you go make sure to dig a very wide planting hole (3 to 4 times or more the size of the root ball of the plant. When digging holes for your plants, I usually recommend adding organic matter in at a 25 to 50 percent ratio with the native clay soil removed from the planting hole. The amount you add will depend on the consistency of the clay. If the clay has quite a bit of sand in it, and crumbles after being squeezed in your hand, add less. For heavy clay soils add more. When conditioning an entire area, till or turn in 3 to 6 inches of organic matter to the native soil. Adding in organic matter should loosen up the clay soil and make your plants very happy.
When you're finished, your garden bed will be several inches higher than it was originally. It will be what is often called a "raised bed." Many plants, especially those that don't like wet feet, appreciate growing in raised beds because there is better drainage.
