How to Grow Your Own Food by Reusing Containers

Have you ever wanted to grow your own food, even though you don’t have suitable land to do so? What about finding a new use for ‘single use’ plastic containers that you already have sitting around? This project outlines a low-cost way to grow your own greens or other veggies (see Note 1) by re-using sturdy plastic containers. This method of growing veggies was first documented by Dr. Kratky (see Notes 2,3).

1. A sturdy plastic container with a lid or opening that is about 3” or larger and a small cup. I used a 32oz Target Good & Gather almond container and a single serving applesauce cup. (see Note 4)
2. Material to grow the seeds in. The plant needs to grow in a material to support its roots. I use rockwool 1.5” cubes that come in a sheet at shown here. I usually cut them in half (sideways as shown) to make them last longer. (see Note 5)
3. The rockwool cubes aren’t enough to fill up the cup, so I also have some expanded clay pellets to fill in the space around the rockwool. (see Note 6)
4. Hydroponic nutrients to nourish the plants. I use “Masterblend 4-18-38 Tomato & Vegetable Fertilizer”. It comes in various sized bags and is a powder. The directions are for a few spoonfuls (12 grams) to be mixed into 5 gallons of water. Magnesium sulfate (the same thing as Epsom salt) and Calcium Nitrate also need to be mixed in. There are many other nutrient brands on the market but this is what I used here.
5. Kit to check and adjust the pH level of the finished solution. The hydroponic solution should have a pH range of about 5.5-6.5. This is quite easy to do. Just take a sample from the mixed solution with the small vial and add a few drops of indicator solution. Compare the resulting color of the sample with the stripes on the bottle to find the pH range. If it needs adjusting, add some pH up or pH down solution until it is within range. (see Note 7).
6. Lettuce seeds or small plants. I jump started the project by using a few seedlings that were already growing outside, but you can also start plants from seed. To use seedlings, I cut a slit in the side of the rockwool and inserted the plant.
7. You will also need some duct tape and an X-ACTO (or similar) knife.

1. Measure and cut a hole in the container lid for the cup to drop into. You want the hole to be large enough for the cup to drop into, but small enough so that the rim of the cup will not fall through. Check that the smaller cup fits into the hole in the lid.
2. If you are using a cup like this applesauce cup, cut holes in it for the roots and nutrients to go through.
3. Cover the container with duct tape or other opaque material. This is because if light gets in then algae will grow in with the roots. I have also seen aluminum foil molded around the outside of containers to accomplish this.

1. Mix up the hydroponic nutrients according to the package directions. Fill the container most of the way full.
2. Place a cube of the rockwool into the cup and use the expanded clay ‘rocks’ to surround and stabilize it. Put a few seeds into the rockwool, or use a pre-sprouted seedling. Top up the container with nutrients so that the rockwool is wet.
3. Place the container outside or inside under a grow light and wait for the lettuce to grow!

As the liquid gets used up plant roots will grow down until they reach the bottom of the container. This can take around 8 weeks or so if growing from seed. A good time to harvest is when the liquid is nearly gone. If you’d prefer to continue growing the lettuce, just refill the container to about 1/2 to 2/3 full. Don’t refill it all the way because the upper roots have developed ‘air roots’ that take in oxygen and need to be exposed to the air. (see Note 1 reference)

I first started these lettuces outside, but due to a stretch of cloudy days I brought them inside underneath a grow light. The video shows growth over a 5 day period. The grow lights were on for 10 hours per day and I edited out the dark periods - that's why the video looks a bit jerky.

Setting the small cup into the container lid as described in Step 1 works well for small plants. However, as the plants grow much larger (see examples in Step 5), the small cup that is connected to the plant's roots will tend to tip over as the plant becomes top heavy.

One way to fix this is to use another ring in between the container and the cup. The extra ring designed for this container was printed with PETG filament. The outer diameter sits on the container opening. The small cup sits in the 3D printed ring. There's a small raised ring on the bottom that fits into the container neck and helps keep the ring in place. Finally, the container lid is screwed on over the cup+ring assembly. The hole in the container lid is a bit smaller than the outer rim of the small cup so that the cup is sandwiched between the ring and the container lid. This will keep it stabilized as the plant grows large!

You can try to adapt this method to many other containers - just use what you have on hand! I prefer to use containers that are between 32oz (1 quart) and 64oz (half gallon) in size.

Since I started this project only about 3-1/2 weeks before the contest deadline, my plants weren't able to grow to their full size by the end. These additional photos are of 2 lettuces and a basil plant that I've previously grown in half gallon glass containers (they have a 3D printed shell around the glass containers to block light). I used the same growing method and materials (nutrients, rockwool and clay pellets) as I've outlined in these instructions. These larger plants took around 2 months to grow from seed.

1. I have successfully grown lettuce, catnip, basil and even tomatoes (in a larger container) using the same nutrients and method.
2. More info and links on Wikipedia: https://en.wikipedia.org/wiki/Kratky_method
3. Link to Dr. Kratky’s YouTube channel: https://www.youtube.com/channel/UCjwBvl5MXuQMziQL2_pQCPA
4. I don’t necessarily recommend the products or brands shown in these instructions - I am just showing the items that I used that I already had on hand.
5. You can find these by searching for “1.5 inch rockwool seed starter plugs for hydroponics”. I understand that they usually have a very low pH as manufactured, so I soak/rinse them in water before using them for planting seeds or seedings.
6. Search for “expanded clay growing media hydroponics” or “Hydroton”.
7. Here is a link to an all-in-one kit to test and adjust pH level. I have found that it lasts a fairly long time – only a few drops of the indicator solution are needed per nutrient batch. https://www.amazon.com/Hydroponics-Advanced-Chemical-Saltwater-Indicator/dp/B078GLP1DC/