Self-Watering Planters

By Sam Burbach, Education & Programming Coordinator – 04/17/2020

JUMP TO INSTRUCTIONS

Need a science project to do at home with the kids? Or do you maybe have a hard time caring for houseplants – either overwatering them or forgetting about them altogether and not watering them until they’re completely wilted? Whether you’re looking for a fun project to do or want a way to keep your houseplants perfectly watered, making recycled self-watering planters is an easy project to try at home!

First, we need to understand how self-watering planters work, and this makes a great science lesson for kids! Self-watering planters work through a process called capillary action, or wicking, which is the same process that plants use to bring water from the ground, up through their roots and all the way up to the highest point of the plant, despite the force of gravity which should pull the water down.

The most basic way to see capillary action in action (no pun intended!) is to dip the corner of a paper towel into a dish of water (colored water makes it even easier to see). The water spreads up through the paper towel as far as it can go until the force of gravity is too strong and the water can no longer climb any higher. While this doesn’t necessarily explain how capillary action works, it is a good visual to show how our self-watering planter is going to work. (If you want to continue with a lesson about capillary action, click here for a more in-depth explanation.)

This self-watering planter uses a wick that will serve as a bridge between a water source and the potting soil. As the plant takes up water through its roots, more water will climb up the wick through the process of capillary action (like how the water climbed up the paper towel), thus making sure the potting media is consistently moist. Watering plants through this method ensures that the roots are evenly moist, promotes deeper root growth, and makes sure the plant does not go through periods of dryness and flooding.

Here’s how you can try it at home!

Here’s what you’ll need:

Plastic bottle – 2-liter bottle, water bottle, etc. (something with a shorter “neck” area – I tried this with an orange juice bottle and the shape didn’t work)
Scissors or utility knife
Sandpaper
Nail
Hammer
Wick material: String/yarn or fabric (scrap fabric, t-shirt scrap, holey sock!, etc.)
Potting mix
Seeds or small plant – something that likes to be consistently moist (cilantro, parsley, mint, African Violets, spider plant, etc.)
Water

Clean out your bottle and remove any labels.

Find the approximate halfway point up the bottle and mark it all the way around. You want the top portion of the bottle to be able to rest upside-down in the bottom portion without the bottle opening touching the bottom.

TIP: Find a can approximately the height of where you want to cut. Place a marker on top of the can, hold or tape marker in place, and spin the bottle around so you can make a straight line all the way around the bottle!

Cut the bottle at your line and sand the edges to make them smooth (this helps with thicker plastic, but doesn’t do much for the thin plastic water bottles). The top piece is now your planter and the bottom of the bottle is the water reservoir.

Create your wick.

String/yarn: If you are using string/yarn, cut a piece that reaches from the top of the planter piece to the bottom of your reservoir plus an extra inch or so. If it’s thin like an embroidery floss cut a couple of pieces, especially if you’re using a larger bottle. Kids can braid it to make it more decorative if they’d like!

Fabric: If you are using fabric, cut a square that will reach from the bottom of the reservoir to approximately half-way up the planter section, or find some fabric to re-use, such as a section from an old t-shirt or what I used – a (clean) holey sock! Cut a few strips into one side so it can be spread out inside the planter.

Insert your wick.

String/yarn: Take the cap of the bottle and use a nail and hammer to poke a hole through the center. (Do this on a piece of wood or outside so you don’t ruin the surface underneath the cap. I did this at our workbench, not the dining room table!) Thread the string through so that it will reach from the top of the planter to the bottom of the reservoir. If the string does not fit snugly, tie a knot on the inside of the cap so it won’t fall out. If you’re using something thin like embroidery floss, knot all the pieces together to feed through the center or poke multiple holes and thread one through each hole. Screw the cap back on.

Fabric: Take the cap off the bottle and push the fabric through the opening. The side with the cut strips should be inside the planter. Make sure it fits snugly. The fabric should reach the bottom of the reservoir and part of the way up the planter.

Fill with potting mix. Take your wick and hold it up as you fill in the potting mix around it. Shake the potting mix down so that it settles into the entire planter, especially if you’re using fabric. Position your wick so that it coils/spreads throughout the planter.

Water the potting mix and wick from the top to evenly moisten it. If you are using string/yarn as the wick, water slowly because the hole with the wick is the only drainage hole for excess water to flow through. If you end up with a puddle of water at the top after a few minutes, carefully pour the excess water out. If you’re using the fabric, the excess water will drip into the bottom reservoir through the bottle opening. This is the only time you will need to water from above.

Sow your seeds or plant your plant. I planted cilantro seeds in two planters and planted my kitchen scrap carrot top in one.

After your self-watering container has had some time to drain any excess water, fill the reservoir with an inch or so of water. Replenish the reservoir as it gets low on water and the wick will take care of watering your plant!