Introduction: Hydrohex Planter

This planter uses passive (Kratky) hydroponics that requires no pumps or electricity. It can be made for a just a few dollars and does a fantastic job growing leafy greens like basil and lettuce. I use this model year round to grow fresh produce in my Alaskan home. It also makes a great project for science fair or classrooms. Let's go.



•Foam Core

•White Glue

•Vacuum-seal Bag-Quart Sized

•2 inch netcup

•1.5 inch Grodon Cube

•Maxigrow Plant Nutrients

•Craft Knife


•Grow Light

•Clay Pebbles

Step 1: Make the Cardboard Base

Find some clean cardboard to make the hexagonal prism base. I am using the top of a copy paper box for this build. Cut the cardboard into a 13 1/2 by 7 inch rectangle. For esthetic reasons, I like the "grain" of the cardboard to run horizontal.

Step 2: Score Prior to Folding

In this step we need to create seven sides to our Hex base. The seventh side has a shorter width and will be used as a glue tab. Put tick marks every 2 1/8 inches. You will need a tick mark at 2 1/8, 4 1/4, 6 3/8, 8 1/2, 10 5/8, 12 3/4. Repeat the marks on the top so you can make straight scoring marks. Use a sharp blade to cut halfway through the cardboard. This allows the cardboard to bend and flex.

Step 3: Creativity

If you are a creative type, this would be the time to add decorations. In my classroom I let students decorate as they wish. Here are a few examples. I also like these felt flower stickers from Amazon.

Step 4: Be Flexible

Bend your joints back and forth a bit so they flex.

Step 5: Glue the Hex

Place glue on the shortest tab. Glue it to the backside of the first 2 1/8 inch side. Allow for a 10 minute dry time. Set aside.

Step 6: Print Templates

Print a template for a foamcore base and top. I use a small hex and a larger hex in my build.

Step 7: Trace and Cut

Trace and cut out two hexagons on 1/8 inch foamcore board. The larger hex will be for the top. I have 3-d printed templates because I make a lot of these for students in my class.

Step 8: Trace a Circle

Find the approximate center of your larger hexagon. Use a two inch netcup to trace a circle. Use your blade to cut the circle. NOTE: Cut the circle slightly smaller than the one you traced so your netcup will seat properly.

Step 9: Glue the Base

Apply a generous amount of white glue to the base of the cardboard hexagonal prism. Place on the smaller foamcore hexagon. Put something heavy on the top while it dries.

Step 10: Extra Support: Optional

Make a few foamcore L brackets. Glue to the inside base and side of the planter. Hot glue can help make this optional step work better.

Step 11: Prepare Your Plastic Liner

Fold back the top two inches to double up the plastic. Place your hand in the plastic bag and push it down into the hex base. I use a couple of paperclips to hold the plastic bag in place. I shove the paperclip down through the cardboard to make the attachment. If you used tough cardboard, you can use your utility knife to create a slit.

Step 12: Nutrients

Add one tablespoon of Maxigrow to one gallon of water. Add nutrient solution to your planter. Fill the plastic bag inside the hex base to within one centimeter of the top.

Step 13: Get Ready for Seeds

Place the lid on the planter. The grodon cubes gets pushed to the bottom of the netcup which sits in the hole you cut out of the larger hexagon. You will notice the cube starting to wick up moisture. Place a few seeds on top of the cube. I like to push a few down into the cube also. You might need to check your liquid level again to ensure it is making good contact with the bottom of the netcup/cube. Add a bit more liquid if necessary.

Step 14: Place in a Warm Location

You don't need sunlight just yet but you do need a warm spot. Also, I like to place something over the top to help the seeds germinate and struggle a bit. Struggling seeds make for better rooting. In this picture I have placed a seed packet on top. If you can remember, spray down your seeds each day with a few squirts of water. This increases the germination success rate.

Step 15: Clay Pellets

If your grodon cube loses contact with the nutrient solution prior to roots developing and extending downward, your seeds won't germinate or seedlings will die. Just keep an eye on this. After a couple of weeks your seedlings will emerge and stregthen. At this point, place a few clay pellets on top of your cube to keep out algae and keep in moisture. Place your planter under a grow light.

Step 16: Celebrate With a Salad

A few weeks later your greens will be ready to harvest. If interested, you can find more passive hydroponic gardening information at Good luck.