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While this question seems simple, it has an incredibly complex answer. What is soil? What forces have a negative impact on soil? At what point is soil considered bad?
Soil does not go bad but it can become unsuitable for plant growth if:
- It is heavily compacted,
- Has extremely high or low amounts of nutrients, or
- Has a significant change in texture or structure.
However, we can usually fix these conditions. Soil is only potentially ruined if it is contaminated by pollutants.
Soil is constantly changing. If you manage it properly, soil should always be improving. However, if you neglect your lawn or garden, the soil may start to lose beneficial properties.
What is Soil?
Soil is a mixture of 5 ingredients:
- Parent material – This is what determines the texture. Soil can have large, medium, or fine particles of parent material, making it sand, silt, or clay.
- Organic matter – Dead leaves, roots, and branches slowly decompose and the basic chemical compounds are reintroduced into the soil. Organic matter is what makes soil spongey and holds water and oxygen while adding nutrients.
- Living organisms – This can be anything from toads to nematodes. Small animals, insects, and microscopic bacteria all work together to break down organic matter and transform it into nutrients for new plants.
- Gas – Soil should be 50% solids and 50% pore space. The pores should have a range of sizes that allow for oxygen and water to penetrate the topsoil and provide moist, aerobic conditions for the living organisms and root systems.
- Water – Without water, soil cannot support plant life. While some plants only need very little water, the soil still has to be able to absorb, hold, and drain water to support plant and animal life. This does not mean soil has to be constantly saturated.
All five soil ingredients should be present in healthy, active soil. An ideal soil has a balanced soil texture, spongey soil structure, a diverse insect and animal population, and an even ratio of oxygen to water.
To learn more, read What Is Soil (And Why Does It Matter).
How Does Soil Go Bad?
Soil doesn’t spoil, but neglected soil can become unbalanced and unable to support plant life.
Planted soils, even if they are neglected, will be much healthier than bare soils.
It is impossible to change the parent material of a soil. You should never try to amend a soil’s parent material by adding sand to clay or vice versa. However, wind and water erosion can wash or blow away lighter soil particles and leave larger particles behind.
This is why most neglected soils are sandy or rocky. An easy way to prevent erosion is by planting bare patches of soil with groundcovers or grass, and watering slowly to prevent runoff.
Low Organic Matter
Soils high in organic matter have a spongey structure due to large amounts of dead, decomposing plant material.
Over time, bacteria break down organic matter into fundamental chemical compounds. If the soil is not replenished with more dead plant material, the organic matter eventually breaks down completely and the soil structure suffers.
This is why it is important to add compost each year; because eventually the compost breaks down and the structure benefits disappear.
Neglected soil will continue to lose organic matter and become more compacted, which reduces porosity and nutrition.
Declining Soil Life
Neglected soil will be unable to support a thriving bacteria, insect, and animal population. As organic matter decomposes, bacteria lose their food source and begin to die off. The soil becomes compacted, which makes it difficult for earthworms, beetles, and other insects to live in the soil.
If the soil is bare, lack of root systems and shade make the area uninhabitable by beneficial insects. As the insect population declines, so does the animal population.
Bare, neglected patches of soil tend to attract weeds and harmful insects that thrive in poor soil.
As organic matter declines, porosity becomes unbalanced. As porosity suffers, the soil loses its ability to hold oxygen and water. These soils either become very compacted, if it’s clay, or drain too quickly, if it’s sandy.
The only way to improve absorption, retention, drainage, and aeration is to add organic matter. Neglected soils without organic matter will lose porosity, and will either erode easily or compact to the point that they are unable to absorb water without intervention.
How to Fix Bad Soil
Luckily, all neglected soils can be recovered and improved. The core reason soils decline is a lack of organic matter, so adding compost back in to any soil will gradually improve all aspects of a healthy soil profile.
Poor soils will start to revert back to their basic texture, so clay soils become compacted hardpans and sandy soils become loose and dry. Both need compost, but they require slightly different recovery processes.
How to improve hard, compacted soil
This is usually the result of an area that has constant vehicle traffic and no water or poor drainage.
The first step is to remove the weeds, either through chemical sprays or pulling them by hand. Weeds that grow in this kind of soil can have large, thick taproots and do not pull out easily. Many can regrow through root fragments left in the ground.
While I’m not a fan of using RoundUp or similar chemicals, this is usually the best route for improving soils like this. Kill the weeds, then start removing the rocks on the surface.
You may need to irrigate the area for a few days before you try to remove weeds and rocks. Use a sprinkler or sprayer and very slowly begin to saturate the topsoil. Water will runoff if you apply too much. Water for 10-20 minutes, take a break for a few hours, then water again. Eventually, the soil will begin to take in water and it will seep into the subsoil.
While the soil is damp, but not muddy, begin to till with a heavy-duty tiller. Rake out rocks and debris as you go. After the first pass, set the tiller a few inches deeper and till again. Keep tilling until you have done a pass on the deepest setting.
Next, add a 3”-6” layer of compost to the area and till or rake it in. You may need more compost if the soil is still blocky.
How to improve sandy, loose soil
Sandy soils attract some nasty weeds- most of which have thorns or stickers. However, the real danger in working with poor, sandy soils is that it has a higher risk of being a home to venomous insects and reptiles. Wear boots and heavy-duty gloves while you work.
Spray or pull the weeds and burn or dispose of them. Never compost weeds you remove from poor, neglected soils.
Rake out rocks and debris and remove them. If your soil has enough structure to need tilling, then irrigate and till the area until you have reached the deepest setting. Extremely sandy soils will not need tilling and you can skip to adding compost.
Sandy soils need much more compost than clay soils if they are going to hold any sort of plant-friendly structure. Add 6”-12” of compost to the area and till it in as deep as you can. When you water, the compost will settle into lower parts of the soil profile because it is so loose, so it will be distributed much deeper than in clay.
Can Bagged Soil Go Bad?
Not really, but bagged soil runs a much higher risk of having pockets of anaerobic activity. Anaerobic refers to a process that happens in an environment with no oxygen.
If soil is inside a plastic bag, and the soil is moist, anaerobic bacteria can begin to grow and the soil will begin to smell.
Is that harmful? No. It stinks, and it can get a weird texture, but as soon as the bagged soil is incorporated into the topsoil in your lawn, the anaerobic bacteria will die and become food for healthy bacteria.
Can You Fix Contaminated Soil?
If your soil has been contaminated by a harmful chemical, you can still try to improve it and reclaim it for plant life. Plants and soil organisms are surprisingly capable of breaking down harmful chemicals, while bare patches of soil can hold on to them for much longer.
Research the chemical pollutant thoroughly before trying any sort of reclamation process. You can follow the same processes as listed above as long as it is safe to be working with the soil in question.
Never try to plant food-bearing plants in soil contaminated by harmful chemicals. Contact an environmental specialist about waiting periods before you consume anything from plants grown on contaminated land.
Any soil that has become unsuitable for plants in the past is at risk of becoming unsuitable in the future if you stop adding compost and following basic maintenance guidelines.