Is It Safe To Compost In Plastic? Garden Tips 2022

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is it safe to compost in plastic

Compost is organic material that we add to the soil to feed plants to encourage healthy growth. You can buy organic compost at garden centers or you can make your own at home. But if you’ve never made compost before, you need to familiarize yourself with some important composting basics, including what makes a suitable compost bin and what you can put into the compost. 

There are many different types of compost bins that you buy or make. Generally, unless you have a lot of space, it’s best to have a bin rather than an open compost pile. But are the many plastic compost bins you can buy safe to use? Since you aren’t composting the plastic, but using it to make plastic, yes they are.  

Can compost be made in a plastic container?

Yes, compost can be made in a plastic container. It’s an excellent material for making compost and for plastic recycling. 

Most commercially available compost bins and composters are made from dark plastic that absorbs heat from the sun. Dark plastic also helps to prevent moisture from escaping.  

Dangers of composting in plastic containers

Because we know that plastic generally can’t be composted, a major concern amongst home gardeners is whether plastic containers are safe for making compost. 

While plastics do produce toxic substances when they degrade, the plastic that is used to make plastic containers for composting is made to last – not degrade. It certainly isn’t biodegradable! More on this later. 

What materials should be avoided when composting?

materials to avoid when composting

A wide variety of yard waste and food scraps can be tossed into a compost bin or onto a compost pile rather than thrown away. According to the United States Environmental Protection Agency (EPA), household waste and scraps comprise more than 30% of what we chuck away with other rubbish.

Using this waste matter for compost keeps it out of landfills. You might think that this isn’t an issue because it’s going to decompose there. But it takes up space in landfills and also releases methane, which is a potent greenhouse gas. 

As the EPA points out, all compost needs three different types of ingredients:

  1. Brown materials including dead leaves and twigs
  2. Green materials including fruit and vegetable scraps, grass clippings, and coffee grounds
  3. Water to help it develop

Main Materials to Avoid

While there is a lot that you can compost, there are certain materials you should avoid. For example, while yard trimmings are a great addition to compost, if they have been treated with chemical pesticides don’t use them. The chemicals may kill beneficial composting organisms.

Pet waste including feces and soiled cat litter, is another no-no. The issue here is that it might contain parasites, germs, bacteria, pathogens, and viruses that are harmful to humans. 

Plants that are diseased or covered in insects should also be avoided. It stands to reason that if they survive the composting process, they could easily be transferred back to other plants. 

Anything that creates odor issues or attracts pests such as flies and rodents should also be avoided. This includes dairy products, fats, oil, lard, or grease, and meat or fish bones and scraps, none of which are “safe foods” when it comes to composting.

Anything that releases or contains substances that are, or might be, harmful to plants. The EPA mentions black walnut tree leaves or twigs and coal or charcoal ash. They don’t specify plastics, but they do have a whole section on plastic recycling and composting in their FAQ.   

Should plastic be avoided when composting?

All plastics are derived from organic products, but the materials used are processed in different ways making some types compostable. So if you’re thinking of composting plastic, you need to be sure you only compost what is compostable. 

It’s confusing to most of us. Some types of plastic are biodegradable, but not all of these are categorized as compostable plastic. 

The EPA advises that most petroleum-based plastic isn’t readily biodegradable. What this means is that it won’t be consumed by various microorganisms which guarantee it is returned to compounds we find in nature. 

Petroleum-based plastic may be designed to biodegrade, but it may only degrade partially. Compostable plastic will biodegrade into what the EPA calls “soil conditioning material.” 

It gets even more confusing because the EPA warns that just because a product is labeled “compostable” doesn’t make it suitable for home composting. This is simply because industrial and commercial composting facilities operate at much higher temperatures than homeowners’ compost bins.  

But not all plastic products are labeled. For example, packing peanuts, which are usually made from plastic and are never biodegradable, are now sometimes made from wheat and corn starches. 

If you aren’t sure, pop one into the water. If it dissolves you can chuck it into the compost. 

But, unless you are 100% sure, avoid any type of plastic unless the label specifies that it is approved for home composting

Can plastic chemicals be absorbed by soil?

A study published online in 2019 states that one of the main problems facing the compost industry is contamination from various plastic waste. Low-density polyethylene (LDPE) used to make grocery bags, sandwich bags, plastic bags, and soft packaging materials is one of the worst.  

Titled Exploring the long-term effect of plastic on compost microbiome, it states that because of its inert nature, its decomposition can take up to 1,000 years.

Plastic chemicals can negatively affect the ecosystem of the soil by releasing toxic substances into the soil. If this happens, the toxic compounds associated with plastic can enter the food chain and affect our health. 

Can plastic chemicals be absorbed by plants?

Yes, they can, and plastic contamination can have really bad effects on seed germination and root penetration. It can also affect water flow and the uptake of nutrients from the soil into plants.

But the problem is when you recycle the wrong types of plastic, not when you use a plastic container to make compost. 

Conclusion

Plastic isn’t something we usually add to a compost pile, but it is a very common material used to manufacture compost bins. So, if you’re looking to buy a compost bin off the shelf, plastic is a good choice.

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