Recently I went to my local landscape supply yard for some blended topsoil. But it occurred to me that I didn’t really know what “dirt” is composed of, so I asked about the ingredients. I was told it’s a mixture of leaf compost, manure compost, mulch compost, creek sand, and screened dirt.
You’re probably thinking, “If all those things are NOT dirt, then what exactly IS dirt, anyway?”
Composition of Dirt
It turns out dirt – or soil – is a complex mixture of several key components:
- Air: the air pockets between soil particles contain gasses like nitrogen and oxygen. Air allows drainage and root growth.
- Clay: made up of sticky mineral particles that tend to hold water. Clay provides nutrients for your plants.
- Humus: decomposed plant and animal matter. Humus improves soil structure and provides nutrients.
- Living organisms: worms, insects, fungi, bacteria, and other microbes. These organisms help create humus and recycle nutrients.
- Rock fragments: these vary in size from stones down to sand and silt granules. These provide structure and drainage.
- Water: from rain along with dissolved minerals and nutrients. Water carries nutrients to plant roots.
The ideal soil composition is 50% solid matter, 25% air, and 25% water. The exact makeup of the solid matter depends on the region, which is why some areas have:
- Clay soil, which holds too much water and can drown some plants. It also hardens to a bricklike consistency during drought.
- Loamy soil, which has the ideal proportion of sand, silt, and clay along with ample organic matter from humus. Loam is crumbly and nutrient-rich, considered the best soil for planting.
- Sandy soil, found near the coast, which drains water too rapidly and is best suited for drought-tolerant plants.
The native soil in my area tends to be high in clay. Because of this, the landscape supply yard blended in some sand and compost to give their topsoil a nicer loamy texture with improved drainage.
For more information and examples, check out our video on soil evaluation. Understanding the components of soil helps you improve your garden.
A soil test from your local extension office or a private lab is the best way to analyze your existing soil. The test results will provide the pH level, nutrient content, and precise ratios of sand, silt, and clay. This helps you determine how to optimize the soil for the plants you want to grow.
For instance, clay-heavy soil may need compost or gypsum to break up the tightly packed clay particles and improve drainage. The test could also show a nutrient deficiency, indicating a need for fertilizers.
Soil tests typically cost $10 to $30 per sample. Here’s how to get started:
Sending a Sample to a Lab
Take samples from several spots around your yard at a depth of six to eight inches. Mix them together for the test to get a representative reading. Avoid sampling immediately after fertilizing or liming, which can skew the results.
The video below reviews a popular DIY soil testing kit and shows how to use it on your lawn:
Improving Soil Drainage
If puddles form easily in your yard or water takes a long time to drain through the soil, you likely have a drainage issue. This is a common problem in clay soils, which get compacted into a dense mass.
Here are some solutions to improve drainage:
- Add two to three inches of compost and till it into the soil, which will help loosen compacted clay.
- Install French drains or drainage tiles to carry away excess water.
- Plant deep-rooted grasses and avoid shallow-rooted ground covers. The deep roots create air pockets in the soil.
For a DIY drainage solution, try digging narrow trenches filled with gravel around your yard. Place perforated drainage pipes in the trenches to channel water away from soggy areas.
Building Healthy Soil
The best soil includes a blend of sand, silt, and clay along with ample organic matter from humus. Here are some tips for improving your soil’s structure and nutrition:
- Grow cover crops like clover or alfalfa, then till them into the soil to increase organic matter. Legumes add nitrogen.
- Regularly add compost, aged manure, shredded leaves, grass clippings, or other organic materials. This feeds soil microbes and provides nutrients.
- Avoid walking on beds to prevent soil compaction. Use boards to kneel on for planting and weeding.
- Mulch beds with two to three inches of organic mulch, like wood chips or shredded bark, to retain moisture and prevent weeds.
- Fertilize according to soil test results to supplement any deficient nutrients. Look for organic or slow-release fertilizers.
Healthy soil leads to healthy plants and better harvests from your vegetable garden, flower beds, and landscaping. Paying attention to your soil pays off.
So, Is Healthy Soil Important?
Soil might seem like an afterthought, but it’s the foundation that all your plants rely on to thrive. Good soil provides drainage, structure, nutrients, and a diverse community of organisms. Taking steps to understand and improve your soil will make your entire yard more vibrant and fruitful.
Test regularly, add organic matter, and adopt gardening practices that protect soil health. The effort is well worth it when you see the results in robust vegetation and bountiful blooms. Do not take soil for granted — nurture it and your plants will flourish.
FAQs About Soil
How do I test my soil?
Use a home soil testing kit or send samples to a lab to measure pH, nutrients, and soil composition. Sample from several spots in your yard at a depth of six to eight inches.
What are the components of soil?
Soil contains rock particles, clay, humus, living organisms, air, and water. The ideal balance is 50% solids, 25% air, and 25% water.
What should I use to fertilize my garden soil?
Choose organic fertilizers like compost, manure, fish emulsion, or cottonseed meal. You can also use slow-release synthetic fertilizers applied according to soil test results.
What can I add to clay soil to improve drainage?
Adding two to three inches of compost tilled into clay soil helps loosen the compacted particles for better drainage. Sand and gypsum are other options.
How often should soil be tested?
Test soil every two to three years to monitor pH and nutrient levels. Test more frequently if making major changes like adjusting pH or improving drainage.