Pesticides can help keep pesky pests and harmful fungus away from your garden. But before you use pesticides on your plants or yard, you’ll need to know how long these chemicals last in soil and familiarize yourself with their potential drawbacks.
Pesticides can degrade within a few hours, but some can remain in the soil for centuries. Pesticide degradation varies depending on pesticide type, soil type, average rainfall, and carbon levels. Pesticides pose multiple risks, so gardeners may prefer to use non-toxic alternatives.
This article will review the factors affecting pesticide degradation and the potential consequences of pesticide use. We’ll also address non-toxic alternatives to pesticides, helping you make an informed decision about how to protect your garden from threats.
Factors That Affect Pesticide Duration in Soil
Determining the half-life of a specific pesticide can be challenging, as several factors impact pesticide duration in soil.
These include:
- Pesticide type
- Soil type and texture
- Average rainfall
- Organic carbon levels
- Amount of pesticide used
Let’s explore these factors in greater detail to discover why they’re crucial aspects in understanding how long pesticides last in the soil.
How Pesticide Type Affects Its Longevity
Pesticides typically fall into one of four categories:
- Insecticides used to kill and repel insects. Common examples include synthetic pyrethroids, neonicotinoids, and carbamates.
- Fungicides used to kill and repel fungus. Common chemical fungicides include propiconazole, myclobutanil, and tebuconazole.
- Herbicides used to kill plant life. Common chemicals used as herbicides include atrazine, glyphosate, and dinoseb.
- Rodenticides used to kill and repel rodents. Common examples include white arsenic, strychnine, and barium carbonate salt.
The longevity of each pesticide type varies depending on its active ingredients.
For example, permethrin (a common insecticide) can remain in the soil for anywhere between 30 and 38 days. However, arsenic (a common rodenticide) can stay in the ground for thousands of years!
Still, pesticide type isn’t the only factor influencing pesticide longevity. Soil type and texture can also impact pesticide degradation.
Soil Type and Texture
There are several types of soils, each with distinct textures and soil pore sizes. These qualities affect how quickly water drains, which impacts the longevity of pesticides in soil.
For example, sandy soil tends to be exceptionally porous. Consequently, pesticides applied to sandy soils may drain into subsoil layers quickly, leaving few traces in the topsoil.
But clay soil has few pores. Therefore, pesticides used on or near clay soils may be unable to drain into subsoil layers, resulting in a longer-lasting presence in the topsoil.
In addition, water is the primary carrier of soil-bound pesticides, so rainfall is also a vital factor to consider.
Average Rainfall
Those living in rainy areas may find that pesticides degrade far more quickly from topsoils. Rainfall can carry pesticides beneath the topsoil and into the subsoil and substratum, resulting in surface soils that contain few long-lived pesticides.
Organic Carbon Levels
Nearly all living creatures are made of carbon. When plants and animals die, their bodies release carbon into the soil. This process generates organic carbon, which is another factor influencing pesticide longevity.
Some types of organic carbon, like charcoal, can bind with pesticides, helping remove them from soils and rapidly decreasing the time they last in the ground.
But, of course, the more pesticides used (especially over time), the more organic carbon required to remove pesticides from the soil.
Amount of Pesticide Used
The amount of any given pesticide used also affects its longevity in soil. The more pesticide applied to an outdoor environment, the more rainfall and carbon required to break it down.
For this reason, professional landscapers and pesticide technicians only apply small amounts of potent pesticides. After all, using too much can have immediate adverse effects on the environment and pose health risks to residents.
Potential Consequences of Using Pesticides in Soil
Gardeners who are considering using pesticides should consider their potential drawbacks.
The most significant of these drawbacks include risks associated with:
- Developing health problems
- Poisoning local wildlife
- Making soil infertile
- Groundwater contamination
Developing Health Problems
Exposure to pesticides can put you at risk of developing both short-term and long-term health problems.
Some of the most common health issues related to contact with pesticides include:
- Nausea
- Dizziness
- Skin rashes
- Throat and eye irritation
- Increased risk of cancer
- Nervous system damage
These acute and chronic effects can be debilitating, painful, and life-shortening. But coming into contact with pesticides (via your eyes, skin, or breathing them in) isn’t only dangerous to humans. It can also harm local wildlife.
Poisoning Local Wildlife
In addition to posing risks for humans, soil pesticides can poison local wildlife. Soils rich in chemicals found in pesticides tend to harbor few beneficial microorganisms and helpful creatures, including earthworms.
Animals that come into contact with pesticide-polluted soil, particularly wet soil, can absorb the dangerous chemicals found in pesticides through their skin. Some of these chemicals can increase the risk of cancer development, and others can result in near-immediate organ failure.
In addition to harming wildlife, pesticides in the soil can also lead to that soil becoming infertile. This means that the affected ground is unable to sustain plant life.
Making Soil Infertile
While some pesticides become inactive after several weeks, others can remain in the soil for years, even centuries. Unfortunately, the average consumer may be unaware that their store-bought pesticide contains long-lasting active ingredients.
These ingredients can build up in the topsoil when reapplied over several months or years, eventually leading to soil infertility and toxicity. When this happens, ridding the soil of its built-up chemicals can be challenging, if not virtually impossible.
Sadly, a heavy build-up of pollutants in the soil can also contribute to contaminated drinking water, making tap water unsafe.
Groundwater Contamination
When rainwater seeps through soil pores, carrying pesticides along with it, it doesn’t simply disappear. Instead, it enters the subsoil and substratum layers, eventually making its way into local groundwater reserves.
Local water management companies often sanitize this groundwater, but some types of pesticides can be challenging to remove. Unfortunately, pesticide use can pollute local groundwater and contaminate local drinking water reserves.
Practical Alternatives to Chemical Pesticides
Since chemical pesticides are associated with a wide range of risks, you may want to try using non-toxic alternatives to common pesticides when working in your garden.
There are several natural options to choose from, many of which post few long-lasting risks to human health or the environment.
Let’s explore some of the most effective of these pesticide alternatives.
Insecticides
Getting rid of insects using non-toxic items is a straightforward process. That’s because most insects are sensitive to salty and acidic environments.
Here are some top-notch non-toxic alternatives to chemical insecticides:
- Baking soda
- Salt
- Diatomaceous earth
- Castile soap
However, since excessive amounts of baking soda and salt can harm garden soil, it might be best to use diatomaceous earth (which dehydrates insects) and a castile soap spray.
Fungicides
Powdery mildew and common molds can wreak havoc on your plants. Fortunately, there are several homemade fungicide recipes you can use to keep fungus from taking over.
The best option depends on the type of fungus you’re fighting. Notably, many ingredients needed to make these sprays are everyday kitchen items, including baking soda, vinegar, and dish soap.
Herbicides
Weeds are a constant problem when working in an outdoor garden. However, chemical herbicides can contribute to premature plant death and remain in your garden soil for years, making it infertile.
If you’re determined to minimize weed growth, mulch is one of the best options. Placing mulch on the exposed ground (while leaving a small space open around plant stems) can prevent most weeds from taking root.
However, wood mulch can retain moisture. This can lead to mold growth, increasing the risk of root rot. For this reason, you may prefer to make your own herbicide spray.
You can make an effective and non-toxic herbicide by combining vinegar, low-cost shampoo, and salt in a spray bottle. Shake the bottle a few times, then aim the spray nozzle at offending weeds and douse them in this solution.
The sodium lauryl sulfate found in most dish soaps and shampoos helps break down the outer plant cell wall, and the vinegar and salt dry out the sensitive interior of the plant. Essentially, this DIY herbicide spray works by dehydrating weeds.
If you would like to explore your options for clearing your garden of weeds, check out my article: How To Make a Garden Weed Free (10 Methods)
Rodenticides
Instead of spraying the soil around your home and garden with chemical rodenticide, you may want to opt to have humane traps installed. Unlike rat poisons or glue traps, humane rat traps don’t kill or harm rodents.
Instead, these devices lure rats to specific areas around your property. When a mouse or rat enters the trap, the entryway door is triggered, forcing it to close. From that point, you can release the rodent yourself (at least 100 yards or 91.44 meters away from your property).
You can also plant rodent-repelling plants along the border of your garden or property.
Some popular options include:
- Mint
- Catnip
- Cayenne
- Camphor
These plants produce strong odors or spicy fruits that can deter rodents from entering your yard.
Final Thoughts
The most common pesticides include:
- Insecticides
- Fungicides
- Herbicides
- Rodenticides
These chemicals can remain in the soil for a few hours or several years.
The half-life of a pesticide varies depending on the type of pesticide, the amount used, soil type, rainfall, and organic carbon levels in the soil. Unfortunately, pesticides can negatively impact human health and the local environment.
For this reason, it may be best to use a non-toxic alternative to chemical pesticides when protecting your garden from weeds, pests, and fungal spores.
