Composting is one of the most effective ways to recycle organic waste, enrich the soil, and reduce your carbon footprint. By breaking down organic material like food scraps, leaves, and other biodegradable items, compost creates a nutrient-rich mixture that can be used to enhance garden soil. But as beneficial as composting is, there are specific items that should never find their way into your compost bin.
Knowing what should be avoided in compost is essential to ensuring a healthy decomposition process and avoiding problems like foul odors, pests, and harmful soil contamination.
Compost is often referred to as “black gold” because of its invaluable benefits to gardeners and the environment. But what exactly is it, and how does it work? Compost is the end result of decomposed organic matter, which is transformed by microorganisms, insects, and fungi into a rich soil amendment.
The Science of Composting:
Composting relies on the interaction of four key components:
- Greens: These are nitrogen-rich materials like fruit scraps, vegetable peels, and fresh grass clippings.
- Browns: Carbon-rich items such as dried leaves, straw, and cardboard fall into this category.
- Water: Moisture is crucial for microbial activity but must be balanced to avoid over-saturation.
- Air: Oxygen enables aerobic decomposition, ensuring the process remains efficient and odor-free.
Together, these elements create the perfect environment for bacteria, fungi, and worms to break down organic material into humus, a dark, crumbly substance packed with nutrients.
The Benefits of Composting Include:
- Enriching soil with vital nutrients like nitrogen, phosphorus, and potassium.
- Reducing landfill waste by diverting food scraps and yard waste.
- Lowering greenhouse gas emissions from organic waste decomposition.
Why It’s Important to Avoid Certain Items in Compost
While composting is a relatively simple process, the materials you choose to include—or exclude—can make or break your efforts. Adding the wrong items to your compost can lead to contamination, slow decomposition, and even environmental harm. Understanding why certain items should be avoided in compost is key to maintaining a healthy and efficient composting system.
1. Contaminants Can Hinder Decomposition
Items like plastic, glass, or metal cannot decompose, leaving behind debris that disrupts the composting process. These contaminants create a waste management issue, as they must be manually removed later, making your compost less usable and environmentally friendly.
2. Harmful Chemicals Can Leach Into the Soil
Some materials, such as treated wood or paper coated with synthetic dyes, contain toxic substances that can leach into your compost and, subsequently, the soil. This contamination can harm plants, disrupt microbial communities, and pose risks to human health if the soil is used to grow edible crops.
Fact: Studies show that compost containing toxic contaminants may exhibit reduced microbial activity and lower nutrient levels, impacting its effectiveness as a soil amendment.
3. Pests and Odors Can Become a Problem
Items like meat scraps, dairy products, or greasy food residues often attract pests such as rodents, raccoons, and flies. Additionally, these materials can emit unpleasant odors as they decompose, making your compost pile less manageable.
4. Disease and Weed Spread
Diseased plant materials or invasive weeds in compost can lead to future gardening problems. Pathogens from diseased plants can survive the composting process if temperatures don’t get high enough, potentially infecting future crops. Similarly, weed seeds may remain viable and sprout once the compost is applied to your garden.
Case Study Example:
A gardening community in the Pacific Northwest reported widespread powdery mildew in their vegetable gardens after unknowingly composting infected squash plants. The spores survived the composting process and spread throughout the soil.
Common Mistakes: What Should Be Avoided in Compost
While composting can seem straightforward, even well-intentioned gardeners often include materials that don’t belong in a compost bin. Knowing what should be avoided in compost is essential for maintaining the health and balance of your pile. Below, we’ll examine common composting mistakes and the items you should leave out.
Non-Biodegradable Materials
These materials won’t break down, no matter how long they sit in your compost pile.
- Examples: Plastic bags, glass bottles, metal cans, synthetic fabrics.
- Why to Avoid: These items persist in the compost pile, creating contamination that can render the entire batch unusable. Sorting them out afterward is labor-intensive and inefficient.
Pro Tip: Look for the “compostable” label on items like packaging or utensils. If it doesn’t say “compostable,” it likely doesn’t belong in your bin.
Toxic Substances
Chemicals can poison your compost and the soil where it’s used.
- Examples: Treated wood, chemically dyed paper, pesticide-laden grass clippings.
- Why to Avoid: These substances can leach harmful chemicals into the compost, affecting soil quality and plant health. Treated wood, for instance, often contains arsenic or copper compounds, which are toxic to microbes and plants alike.
Data Insight: Research indicates that compost containing heavy metals like copper and arsenic may reduce crop yields by up to 30%.
Animal Products
These materials can lead to unpleasant side effects.
- Examples: Meat scraps, dairy products, fish bones, greasy leftovers.
- Why to Avoid: Animal products attract pests like rats and raccoons and create strong odors during decomposition. They can also disrupt the balance of nitrogen and carbon in your compost pile.
Alternatives: Consider vermicomposting for small amounts of eggshells and dairy-free scraps, as worms can safely break these down.
Diseased Plants and Invasive Weeds
Plant pathogens and weed seeds can cause long-term problems.
- Examples: Tomato plants with blight, dandelions with mature seeds, or crabgrass.
- Why to Avoid: Diseases can survive in the compost and spread to your garden. Similarly, weed seeds may not decompose fully, leading to an outbreak in your soil.
Pro Tip: If you’re unsure, dispose of diseased plants and invasive weeds in the trash or burn them, where permitted.
Human and Pet Waste
Organic doesn’t always mean safe.
- Examples: Cat litter, dog feces, diapers.
- Why to Avoid: Human and pet waste often contain harmful pathogens that can pose serious health risks if not properly treated. Unless you’re using a specialized hot composting system, these materials should stay out of your pile.
Certain Kitchen Scraps
Not all food waste belongs in compost.
- Examples: Citrus peels, onion skins, garlic, large amounts of bread or rice.
- Why to Avoid: Citrus and garlic can upset the microbial balance in your compost due to their acidity and antimicrobial properties. Bread and rice can quickly become moldy or attract pests.
Solution: Add these items sparingly if you must, and balance them with ample carbon-rich “browns” like dry leaves or cardboard.
Specific Items to Avoid in Compost
When it comes to what should be avoided in compost, there are specific items that stand out due to their detrimental impact on the composting process. Below is a detailed list of materials you should exclude from your compost bin, along with explanations for why they don’t belong.
1. Glossy or Coated Paper
- Examples: Magazines, brochures, junk mail with shiny finishes.
- Why to Avoid: Glossy paper is often coated with plastic or chemical inks that do not break down naturally. These coatings can introduce microplastics and toxic residues into your compost.
- Better Alternative: Shredded, plain, non-dyed paper or cardboard.
2. Synthetic Fabrics and Materials
- Examples: Polyester, nylon, spandex.
- Why to Avoid: These materials are not biodegradable and will remain intact in your compost indefinitely. Even items labeled as “biodegradable” may require industrial conditions to break down.
- Pro Tip: Only natural fibers like cotton or wool (without chemical treatments) are suitable for compost.
3. Pressure-Treated Wood
- Why to Avoid: Pressure-treated wood is infused with chemicals like arsenic or copper to prevent rot. While these treatments prolong the life of wood, they release harmful toxins into the compost, which can be detrimental to plant health.
- Solution: Recycle untreated wood for garden paths or raised beds instead.
4. Large Woody Materials
- Examples: Thick branches, logs, or large chunks of wood.
- Why to Avoid: Large woody items break down extremely slowly and can disrupt the balance of your compost pile. They may also make turning and managing the pile more challenging.
- Alternative Use: Chop wood into small chips or shavings before adding it to compost.
5. Dairy Products and Grease
- Examples: Milk, cheese, yogurt, butter, oil, or greasy leftovers.
- Why to Avoid: These items can create strong odors, attract pests, and lead to anaerobic decomposition, which slows down the composting process. Grease can also coat organic material, making it harder for microbes to break it down.
- Pro Tip: Use paper towels soaked with small amounts of cooking oil as “browns” if necessary.
6. Compostable Plastics
- Why to Avoid: Despite their name, most compostable plastics require industrial composting facilities to break down. In home compost systems, they can linger for years without fully degrading.
- Solution: Check local composting programs that accept these materials.
7. Diseased or Pest-Infested Plants
- Examples: Plants with mildew, rust, or blight, and leaves infested with aphids or mites.
- Why to Avoid: Many pathogens and pests can survive the composting process, especially if the pile does not reach high temperatures (131–170°F). These contaminants can infect future plants.
- Pro Tip: Use hot composting methods or dispose of these materials in green waste bins provided by municipalities.
8. Weeds with Seeds
- Examples: Dandelions, crabgrass, or thistles with mature seed heads.
- Why to Avoid: Weed seeds may not decompose and can sprout when the compost is applied to your garden, leading to a new weed problem.
- Solution: If weeds are still young and seed-free, they can be safely composted.
9. Leftover Processed Foods
- Examples: Chips, cookies, or anything with high sugar or salt content.
- Why to Avoid: These foods can attract pests and slow down decomposition due to their preservative content. High salt levels may also harm plants when compost is used in soil.
Quick Reference for Items to Avoid in Compost
| Item | Why to Avoid | Alternative |
|---|---|---|
| Plastic bags | Non-biodegradable; contaminates compost | Use reusable containers for kitchen scraps |
| Meat and fish scraps | Attract pests; foul odors | Dispose in sealed trash or compost industrially |
| Glossy paper | Contains plastic coatings | Use plain paper or cardboard |
| Diseased plants | Spreads pathogens | Use hot composting or dispose in trash |
| Synthetic fabrics | Won’t break down | Recycle through textile programs |
Avoiding these specific items in your compost is critical for creating nutrient-rich, high-quality compost that supports a healthy garden.