Safe Plastic For Hydroponics: What To Use + Avoid

As the weather gets colder where we live, my wife and I thank our stars we’ve gotten into hydroponics. 

It lets us keep growing plants all year long without worrying about soil in our home. 

We’ve enjoyed designing and making our own systems too, but I’m always safety conscious. I know not every plastic is safe when exposed to water, heat, and light. 

I researched safe plastics for hydroponics, and what I found surprised me. 

The safest plastic for hydroponics is tied between High-density Polyethylene (HDPE) and Low-density Polyethylene (LDPE). Both are safe and usable under high heat, water, and light without releasing any chemicals. HDPE is more recyclable and more environmentally friendly, so it’s a more popular option. 

There are other plastics out there to check out. Look ahead for our deep-dive into all the options to consider. 

What Are Safe Plastics For Hydroponics? 5 Options To Check Out

When water is warm, and in contact with plastic for a long time, you want to make sure it doesn’t absorb any bad chemicals and pass it on to your plants. 

With this in mind, here are some safe plastics you’ll want to consider in table form. For the details, keep reading after. 

Plastic Type	Verdict
High-density Polyethylene (HDPE)	Very safe, just make sure it doesn’t use a mold release agent.
Low-Density Polyethylene (LDPE)	Very safe, not as easily recycled.
Polyethylene Terephthalate (PET or PETE)	Safe and great for recycling, but not designed for a lot of use.
Polypropylene (PP)	Safe, but doesn’t handle high heat as well.
Polyvinyl Chloride (V or PVC)	Considered safe in some forms, but new research shows it may leak more chemicals than previously thought.

High-Density Polyethylene

High-density polyethylene is also called HDPE and is commonly referred to by the number “2” for plastics. 

As a general rule, HDPE is one of the safest plastics for any use. It doesn’t spread chemicals through water contact, and it’s also one of the more eco-friendly options as it’s easily recycled. 

Most milk and water jugs, juice bottles, yogurt containers, and other food-related plastics are made of HDPE because of their safety. 

For extra safety, make sure the HDPE #2 plastic container is also food-grade plastic. This means it’s USDA, FDA, or NSF approved. 

Other #2 plastics may contain a “mold release agent” to help release the plastic from the mold shape. 

This agent is not graded for food, so while it’s probably OK for hydroponics, you may want to opt for a food-approved option to remove any risk. 

HDPE #2 resists UV rays, and it handles high heat well without melting or giving off chemicals. 

Verdict: This is one of the best options and the safest for plants. It’s proven not to bleed any chemicals into the water. 

AeroGarden makes its units out of this plastic. Check out our review of the best AeroGarden for lettuce and small herbs. 

Low-Density Polyethylene

Low-density polyethylene is also called LDPE, and it’s similar to its older and more dense counterpart discussed above. 

It’s another food-grade plastic in many cases and is marked as plastic #4. 

You’ll see these in: 

• Bread Bags
• Frozen Food Bags
• Squeezable Bottles 
• Trash Can Liners
• Food Storage Containers

As a general rule, if plastic is good enough to use with food, it’s great for gardening. 

It’s not known to contain any carcinogens (which cause cancer), but it’s not as well recycled as types #1 (PET) or #2 (HDPE).

Verdict: Here’s another safe plastic option for gardening, but if you want to be extra environmentally friendly, check out another choice. 

Polyethylene Terephthalate (PET or PETE)

Polyethylene terephthalate is also called PET or, more rarely, PETE and is referred to as a #1 plastic. 

It’s most commonly seen in: 

• Soda bottles
• Water
• Sports drinks
• Ketchup
• Mustard
• Dressings
• Peanut butter

If it’s a single-use plastic container meant to break down and recycle, it’s a PET #1 and safe for gardening. 

However, while it’s not known to give off any chemicals normally, it’s also not meant for heat, a lot of light, and repeated use. 

As such, it absorbs the odor of whatever’s inside it, so the fertilizer may pose an issue. 

Check out using normal fertilizer with hydroponics and why you may not want to try this.  

Hydroponic reservoirs need to be used with a water-nutrient solution over and over. 

Verdict: While it’s most likely safe to use, it isn’t designed for reuse, heat, and light, all of which are part of the hydroponic system. 

Polypropylene

Polypropylene is also known as PP and is called plastic #5. 

It’s one of the safer plastics for your hydroponic system. 

There are some who debate the safety of the plastic overall as PP is known to release harmful during manufacturing, but once this is done, it releases a minuscule amount of chemicals.

This plastic is also used with some food elements such as straws, bottle caps, and some food containers such as yogurt containers. 

The biggest drawback of PP #5 is that it isn’t recycled widely, so it’s one of the least environmentally-friendly options on the list, though it’s safe. 

When it comes to higher levels of heat, PP isn’t as tolerant at HDPE or LDPE, but it’s more than enough to handle the heat from hydroponics. 

Verdict: While this plastic is largely considered safe, it doesn’t recycle well, and there are plastic options that handle heat better. Use it if you wish; it won’t harm anything.

Polyvinyl Chloride (V or PVC)

Polyvinyl Chloride is known as V or PVC plastic and is one of the widest known plastics out there. Technically, this is also plastic #3. 

It is used in some food-grade forms, mostly as a cling wrap for meats and cheeses. 

We most often find this plastic in places like: 

• Plastic pipes
• Irrigation
• Liquid detergent containers
• Thicker containers
• Flexible shaped pipes

During the most common form of PVC, the manufacturers need to add something called a “plasticizer.” This makes the plastic flexible and workable into its many shapes. 

Research has definitively found these plasticizers, called phthalates, will leak out when in contact with water and foods. 

A chemical called DEHP, a main part of this PVC process, is suspected to be a carcinogen in humans. Carcinogens are chemicals that cause cancer. 

This is made worse by how much more leakage there is when the plastic is exposed to water, heat, and light. 

Since we use all of this in hydroponics in its different forms, those chemicals will leach into your plants, and if you grow edible plants for later, you could end up eating it.

Learn about the forms of hydro- systems by checking out our detailed comparison of Aeroponics vs. Hydroponics vs. Aquaponics. 

As a building material, PVC works well, but it’s not great for use where you may end ingesting something in contact with it. 

Not every PVC uses these plasticizer chemicals, but many do, and more than we may realize. There’s a big push to remove the use of this plastic altogether. 

Verdict: Don’t use it. Theoretically, it’s safe in some forms, but more research is coming out showing even “safe” PVC may not actually be free of chemicals and leakage. 

Parts In A Hydroponic System

Of the parts in a hydroponic system, the hydroponic reservoir, the growth deck, and any pipes you use are the ones you need to worry about for plastics. 

Let’s look briefly at all the parts of the systems. 

• Hydroponic Reservoir – This is the tank where you keep your hydroponic water and nutrient solution. It comes into contact with water the most. 
• Water Solution – Water mixed with liquid fertilizer containing nitrogen, phosphorus, potassium, and other trace minerals. 
• Growth Deck – This is where you store your plants as they grow. It’s below the grow lights and often contains a place for the water solution to come through. 
• Grow Lights – Grow lights are special UV and possibly LED lights that simulate the sun and help plants go through photosynthesis. 
• Seed Pod – This is a container that holds the seeds and fits into the growth deck. 
• Air Pump – Air pumps add oxygen to the water solution and keep it moving to prevent mold and algae. 
• Water Pump And Pipes – Water pumps are needed in most variations of hydroponics as they move your solution from the hydroponic reservoir to the growth deck for the plants. 
• Growing Medium – Plants need something to grow in. Often, this is an organic material made of other plants, though Rockwool is also popular. Learn how to use Rockwool in hydroponics.