One of the more common questions I’m asked on the blog is about plastic use, specifically, “What plastics are safe for use in the garden?” Since a lot of Epic Gardening readers are into hydroponics and aquaponics over soil gardening, there are a lot of people with a lot of plastic in their setup that are curious about their safety and place in the garden.

Well, I was curious too, so I decided to go deep into the world of plastics and figure it all out for you all!

Listen to this post on the Epic Gardening Podcast

Subscribe to the Epic Gardening Podcast on iTunes

Here’s what I found. It turns out there are 7 different types of plastics that are labeled. If you’ve ever seen those little triangles with a number in it on your plastic products, you’ll know what I’m talking about. Here’s a picture:

Below is a breakdown of what each type of plastic is, what products use it, and if it’s safe to use in the garden.

Plastic Type 1 – PET

Plastic marked with a 1 is made of Polyethylene Terephthalate, or PET. It’s one of the most common plastics for food items like soda bottles, jars of peanut butter, or if you’re like me, jars of ghee you use for cooking. One of the issues with this type of plastic is that it tends to take on the aroma of the food that is stored in it.

It’s one of the most commonly recycled plastics and is almost exclusively used for single-use items since it can break down when exposed for long periods of time to light or heat.

If you’re paying attention, that means it’s not the best choice for your garden, since ​gardens typically are exposed to quite a bit of light and heat!

Yes, it’s probably going to be fine, but why take the chance of some leaching, especially when you’re running a soil-free setup, meaning that the leached chemicals will go straight into your reservoir rather than the bit of soil next to the plastic.

Verdict: While it’s probably OK to use, there are better plastic choices out there, so why not use those instead?

Plastic Type 2 – HDPE

Plastic marked with a 2 is made of High-Density Polyethylene.​ You see HDPE everywhere, from milk jugs to detergent bottles. It’s one of the best and safest types of plastic for food consumption as it resists UV rays and is extremely heat tolerant ( -148 to 176 F / -100 to 80 C ). Because of this, it’s an excellent choice for the garden.

Verdict: Very safe, not known to transmit any chemicals into soil or food. An excellent choice for the garden.

Plastic Type 3 – V

Plastic marked with a 3 is made of Polyvinyl Chloride​, better known as PVC. One of the more commonly known types of plastic, PVC shows up in plastic pipes, irrigation, salad dressing bottles, and liquid detergent containers.

Most PVC products contain chemicals known as phthalates, which essentially help the PVC be more durable, flexible, etc – all of the qualities we associate with plastic.​

While this is great for making PVC a quality building material, phthalates are not the best for us humans. In fact, most of us have some small concentration of phthalates in our urine due to leaching, though the CDC believes that our diet is the reason for most of the phthalates in our bodies.​

For this reason, try to stay away from PVC setups in your gardens. I know it’s attractive to have a cheap PVC garden, but if you value your health, choose an alternative plastic.

*Note: not all type 3 plastics use phthalates as a plasticizer, so you may be OK using some PVC products – but be sure you know that phthalates weren’t used before you make the decision.​

Verdict: We’re already exposed to enough phthalates in our daily lives, why grow with a material known to leach them into the environment?

Plastic Type 4 – LDPE

Plastics marked with a 4 are made with Low-Densidy Polyethylene. Some products that use LDPE include plastic produce bags, trash can liners, and food storage containers.

Are you seeing a trend here? The plastics that are already used for food storage tend to also be safe to garden with. Like it’s older cousin HDPE, LDPE plastic is very safe in a wide range of temperatures and can even be used in the microwave. Conclusion? It’s a good choice for the garden.

Verdict: Very safe, not known to transmit any chemicals into soil or food. An excellent choice for the garden.

Plastic Type 5 – PP

Plastic marked with a 5 is made of Polypropylene​. Commonly used in products that require injection molding like straws, bottle caps, or food containers. While it’s not as universally tolerant to heat as HDPE or LDPE, it generally is safe for use with food and the garden.

There are some minor concerns about leaching that came up after Canadian researchers found that the leaching was affecting their labwork, but for the most part it’s regarded as a safe plastic ​

Verdict: A decent choice for the garden.

Plastic Type 6 – PS

Plastic marked with a 6 is made of Polystyrene​. You see polystyrene based plastic everywhere – packing peanuts, styrofoam cups, plastic forks, meat trays, to-go containers, etc. It’s one of the most widely used types of plastic in a variety of industries.

​Being so widely used, it’s also been the subject of many scientific tests on health and safety. The general conclusion is that it’s safe for use in food products, which doesn’t necessarily mean that it is safe for gardening.

One interesting fact is that the food products that are contained in polystyrene (meat, berries, etc) all have styrene as a naturally occurring compound. Polystyrene is a continual topic of discussion in scientific circles due to it’s wide use. One particularly popular topic is the safety of microwaving polystyrene products with food – the jury is still out on that one.

All in all, it’s a decent plastic to use for the garden, but my only concern is that it is a more porous material and less sturdy, making it not a good structural choice for the garden.​

Verdict: Seems fine safety-wise, but structurally may not be the best choice for the garden if you need it to support weight or water.

Plastic Type 7 – OTHER

Plastic marked with a 7 is made from anything other than the materials listed in numbers 1-6. Typically this means plastics made of Polycarbonate or Polylactide​. Polycarbonate is the most common type 7 plastic, and also one of the most harmful plastics that we have ever created. It’s been proven time and time again to leach BPA, which has been linked to a lot of different health problems.

The thing to know about plastic type 7 is that it’s a catch-all for anything that doesn’t fit into the first 6 categories. That means that there are also some safe plastics in this category as well, but you’ll have to do further research to make sure that you’re using one that’s safe.

Why go through the trouble when there are other, safer plastics to use like HDPE or LDPE? My vote is to stay away from type 7 in the garden simply due to better options elsewhere.​

Verdict: Some type 7 plastics contain BPA, a harmful compound that has been linked to many adverse health effects. Stay away from type 7 plastics in your garden.

Which to Choose?

Hopefully this breakdown gives you a good idea of what to look for when it comes to using plastic in the garden. I’m all for recycling materials and using what you can to build out your garden, but not at the expense of your health or the health of the people who are eating what you’re growing!

My personal choice is to go with HDPE or LDPE, just because they’re the safest by far when it comes to actual scientific tests and potential concerns. Yes, they’re a bit more expensive to purchase, but they last a long time, which means they’re actually cheaper when you consider the fact that you won’t have to replace them often.

Have any thoughts or suggestions about plastic use in the garden? Let me know below!

The Green Thumbs Behind This Article:

Kevin Espiritu

Founder

Clarisa Teodoro

Researcher