Garden soil is much more than simple dirt. If we take a close look at its makeup, we find that garden soil is a mixture of mineral particles, organic material, moisture, living organisms, and chemical nutrients. One of the most critical factors in a soil’s ability to support life is its texture. Depending on the size of the soil particles, the texture can range from very porous and well-draining to extremely dense and resistant to water movement.
We refer to dense soil as clay, because most of its mineral particles are very fine clays. Ideal garden soils, sometimes known as loamy soil, are a mixture of sand, clay, mineral particles, and most importantly, organic material. To truly understand the importance of soil, we have to take a closer look at its ingredients.
The Living World Beneath Your Feet
Soil microbiology is the study of all microorganisms that exist in the soil, specifically the ways they function and affect soil properties. Our soils are teeming with life, serving as excellent hosts for the growth and development of plant life. In fact, there are more microbes in one teaspoon of soil than there are people on Earth, and soil provides shelter for around one quarter to one-third of all living organisms on the planet.
This collection of organisms consists of bacteria, fungi, and algae that serve important roles in the overall health of soils. Biodiverse soils consist of organisms that increase soil fertility, convert nitrogen from the air so it can be absorbed by plant roots, and mineralize nutrients. The community of organisms in soils ranges from microscopic microbes to earthworms and ants, all serving important roles in soil health. To achieve the maximum benefit from our gardens, landscape beds, and lawns, it is essential to support these complex ecosystems in order to preserve and promote fertile soils.
Bacteria, Fungi, and Earthworms
Within just one handful of soil live around 100 million bacteria. These bacteria are largely responsible for converting nitrogen in the air into compounds that can be absorbed by plant roots. Fungi, though less abundant, assist with extremely important functions of soil health. Their main activities include decomposing organic matter and aiding water and nutrient cycling. Fungi are also responsible for binding soil particles together and improving water filtration and water-holding capacity.
Earthworms break down organic matter such as dead leaves and produce natural fertilizers. They support soil fertility by transporting water throughout the soil and creating tunnels that allow air and water to flow freely.
The Problem with Synthetic Fertilizers
We receive requests daily during the planting season to check soil pH, and frankly, most samples we see are either lifeless, powdery, and compacted, or heavy chunks of wet clay. Neither is optimal for plant growth, and both will take some effort to correct.
One cause of soil failure is the overuse of synthetic fertilizers. Fertilizers are of two types: organic (or natural) and inorganic (or synthetic). Organic fertilizers slowly leach essential nutrients into the soil and improve its overall vitality over time. Synthetic fertilizers supply consistent amounts of precise nutrients immediately, which is especially beneficial for dying or severely malnourished plants, and they are easy to use and readily available.
The problem is the long-term effect. Synthetic fertilizers kill beneficial microorganisms that convert organic material into nutrient-rich matter. With the microorganism population gone, plants become reliant solely on synthetic fertilizers and the soil becomes less and less hospitable to plant life. We see this most often in lawns: hard-packed soil that resists a shovel but turns to lifeless powder when struck with a pick. This can be repaired. We can rebuild and replenish the natural biodiversity of this type of soil, the same way we convert heavy clay soil into a hospitable environment for our Mid-South landscape.
Understanding Clay Soil
Clay soil is prevalent in many parts of the United States, and it can be challenging if you are trying to grow a flower or vegetable garden. While some trees and shrubs grow well in clay, most annuals, perennials, and vegetables do not have roots strong enough to force their way through dense clay. Spring flower bulbs tend to rot over the winter in wet clay soils.
Clay soil is defined as soil comprised of very fine mineral particles with little organic material. The resulting soil is sticky and does not drain well. If water tends to puddle on your ground rather than soak in, you likely have clay. Soil that consists of over 50 percent clay particles is referred to as heavy clay. You may already know if you have it: the soil sticks to your shoes and garden tools like glue, or forms big clods that are not easy to separate.
Clay is not without its benefits. Because of its density, it retains moisture well and tends to be more nutrient-rich than other soil types, containing high levels of calcium, potassium, and magnesium.
How to Improve Your Soil
Improving clay soil, or soil that has been depleted by overuse of chemical fertilizers, takes some work, but the results are immediate. Most of the work is done up front, though some maintenance is necessary to keep your soil at its peak.
It is best to improve an entire planting area all at once rather than amending individual planting holes as you need them. In an existing bed, you can amend each planting hole with compost. Adding organic compost on the surface of areas where you did not plant is just as important as adding it where you did. All of the nutrient content of the compost will leach into the ground, feeding the beneficial microbes in the soil. Over time, adding compost to your garden the way you would add mulch will produce a noticeable difference in plant health and productivity.
Starting a New Bed
If you are adding a new landscape bed or starting a vegetable garden, you will need to add 6 to 8 inches of organic matter to the entire bed. Grass clippings (as long as they have not been treated with chemicals), shredded leaves, rotted manure, and compost are all good choices. Spread your organic matter on top of the soil and mix it into the top 6 to 12 inches of soil. A shovel works well, or if digging is too hard on your back, a tiller is fine.
When you are finished, your garden bed will be several inches higher than it was originally. This is not a problem. The bed will settle over the course of a season as the organic material breaks down. The soil structure will continue to improve as microorganisms work to break down all of the organic matter you have added.
The bed can be planted immediately. Plan to add more organic matter in the form of compost once or twice a year. This will continue improving the soil structure and offset any settling.
What Not to Add: A Note on Sand
People often imagine that the proper way to improve dense clay soil is to add the opposite type of mineral material: sand. After all, loamy soils are a mixture of sand and clay. Unfortunately, when sand is added directly to clay, the result is something closer to concrete. Loamy soils are great for plants because they have a large ratio of organic material as a foundation for the sand and clay. Without lots of organic material, clay plus sand equals a poor garden. Clay soils are best improved with the addition of compost and other organic materials.
Testing and Long-Term Maintenance
After a season or so, collect a soil sample and have it tested to check for any nutrient deficiencies or pH issues. The report you get back will offer suggestions for further improvement. Add any organic fertilizers or soil amendments outlined in the report and your bed will continue to be productive for years to come.
Organic material will need to be continually added to prevent your garden from returning to its heavy clay state. Rather than cleaning your garden down to the soil line each fall, allow leaves and other plant material to decay naturally and become part of the ongoing ecosystem of a good garden soil.
Lawns and Larger Areas
On lawns and large landscape areas, fertilizers like Milorganite provide an organic boost to microbe populations and are a great source of natural nitrogen and iron. Products like Fox Farm Microbrew, Kangaroots, or any of the plant-specific Espoma products will increase the microbe population in your soil. Natural Guard Soil Activator is a highly concentrated organic soil conditioner that provides humic acids to stimulate nutrient uptake and soil microbial life. Humic acid also promotes strong, healthy root development.
In the Mid-South, it is generally accepted practice to aerate our lawns once a year. A machine that pulls up plugs is preferred over solid spikes. Once the soil has been opened by aeration, this is the perfect time to spread a layer of compost over your lawn. Back to Nature Cotton Burr Compost, Back to Nature Blend, or Back to Nature Cow Manure are excellent sources of the natural organic materials your lawn needs.
The periodic use of chemical fertilizers for a quick boost is acceptable. However, use products that are slow release and specific to your needs.
No matter the condition, we can improve your soil and help you have a productive vegetable garden or landscaping that will be the envy of the neighborhood. It all truly begins with the soil.