Build a PET water bottle hydroponics system (7 steps)

Building a water bottle hydroponic system using a PET bottle is probably the easiest and most budget-friendly way to get started with hydroponics.

The system you will build here works great for growing herbs and leafy vegetables like lettuce, kale, and arugula (rocket).

7 steps to building a budget DWC bottle hydroponic system

Rather than using hydroponic grow beds, reservoirs, air pumps, net pots, and grow lights, we focus on using things you may already have at home. The whole idea is for you to be able to get started right away.

If you do not fancy DIY, check out the small indoor hydroponic systems I use and recommend.

1. Materials needed for water bottle hydroponics

We need a plastic PET bottle, a sharp knife, water, hydroponic liquid fertilizer, and a firm medium like LECA (or Hydroton clay pellets) to build this budget-friendly hydroponic system.

We use plastic bottles made from food-grade PET or Polyethylene Terephthalate. [1]

Ensure that any plastic you use when growing herbs and vegetables is food-safe.

2. Prepare the bottle

Cut off the top 1/3 of the bottle to create a cup (or pot). This cup will serve as a grow bed and will hold the LECA and the plants we will grow later on.

Next, cut off the screw top to make a slightly bigger opening. But do not make the opening too big. You do not want the LECA to fall into your base container (bottom of the bottle).

The larger 2/3 part of the bottle will serve as our reservoir and will hold our water and nutrient solution.

3. Make holes in your grow bed (top 1/3)

I use a soldering iron to make the holes but it can also be done with a knife or a pair of scissors. Please be careful not to hurt yourself or others.

Make sure that no hole is big enough for the LECA pebbles to fall through.

4. Add water and nutrients to the reservoir (bottom 2/3 of the bottle)

Fill the bottom of your bottle with water and add liquid nutrition per instructions (see manufacturer’s recommendations).

Ideally, you use liquid nutrition for hydroponics. It does not cost a lot and goes a long way. If not, use half the recommended dosage of any organic fertilizer you have.

If you use pellets, make sure you dissolve them in water before adding the liquid to the reservoir.

Related: Learn how measuring EC levels can help you monitor the nutrional strength in your water.

5. Add LECA pellets to grow bed (top 1/3 of the bottle)

Fill the top 1/3 of the cup – your grow bed – with LECA that has been soaked in water.

Place some bigger pieces of LECA in the bottom of the cup to ensure that the LECA stays put in the cup.

6. Prepare and plant seedlings in grow bed (top 1/3 of the bottle)

Prepare your seedling by cutting off all but the top leaves. Here we are using a Thai basil cutting, but you can use any herb or leafy green vegetable.

Plant your basil seedling in the cup and mount the LECA to support the seedling.

See bottom of article if you prefer starting from seeds. 

7. Place grow bed (top 1/3) inside the reservoir (bottom 2/3)

Place the top 1/3 of the bottle, or grow bed, holding your cutting inside the reservoir, or the bottom 2/3 of the bottle.

Make sure that about 2/3 of the LECA in the grow bed (top 1/3) is submerged in the water and nutrition solution.

Next, cover the bottom part of the bottle with paper or cloth. As we add nutrients to the water we need to block out light to prevent algae from developing in our reservoir.

And that’s it. You are done.

Finishing touches

You need to ensure that the bottle hydroponics system has adequate light and that the seedling does not dry out.

The easiest way is to ensure that you submerge 2/3 of the grow bed LECA into the water nutrient solution. This way, the seedling´s roots should always have access to water, nutrition, and oxygen.

Place your hydroponic system in a location with about 6-8 hours of direct sunlight per day. Using a grow light will give you healthy growth and a vigorous plant during the darker months of the year.

Do not worry if the LECA dries out on top.

You are fine as long as part of the seedling´s stem is in contact with water. And before too long you will be able to see how the roots of the basil seedling reach the water in the container.

Starting from seeds instead of seedlings

You can, of course, also grow basil from seeds in your budget-friendly water bottle hydroponic grow system.

Instead of placing the seedling in LECA we plant seeds on the moist LECA.

It is essential to keep the LECA moist – even on the top. Making sure that almost all the LECA is submerged in water.

If the LECA shows tendencies to dry out on top you use a spray bottle to add moisture. Covering the top with plastic wrap is often helpful in controlling the level of moisture.

Apart from this detail, the steps above remain the same.

Hydroponics made simple – for a reason

The water bottle hydroponic system we build introduces the concept of the Deep Water Culture (DWC) hydroponic growth systems.

And there is a reason we are trying so hard to use things you probably already have at home. 

We are trying to make the point that there is no magic to hydroponics.

Hydroponics may sound fancy and complicated, but there are more similarities than differences compared to traditional growing with soil as the medium.

You can read my other guides for more information on hydroponics and how to build different types of hydroponics grow systems like Deep Water Culture (DWC) and Ebb and flow hydroponic systems

What is medium or substrate?

Medium or substrate are just different names for anything that plants can grow in or on.

Soil is a medium (or substrate) that everyone knows about. But water is also a medium. And as it happens, water is the medium of choice when we build a hydroponic grow system.

What is LECA?

LECA is a growing medium made of small, baked clay balls. The abbreviation LECA stands for Lightweight Expanded Clay Aggregate.

LECA is porous and absorbs water but is also what we call inert. Inert, simply put, means that LECA has specific attributes (porous and, absorbs moisture) but will not break down or provide any nutrients to the plant.

And this is a good thing as we want the medium to help us deliver the nutrients we add and to help create a healthy balance of moisture (absorbs water) and oxygen (porous).

You can, of course, use rock wool or coconut coir if you prefer. I happen to prefer LECA as it is inexpensive and easy to work with.

Tip! Wash your LECA thoroughly before use. LECA may look clean but even the more expensive LECA made for hydroponics needs to be washed to remove dirt and grit.

Helpful sources:

[1] https://www.americanbeverage.org/education-resources/blog/post/what-is-pet/