The word hydroponics comes from the Greek roots hydro for water and ponos for labor. That means that in this type of gardening, you let the water do the work.
In a traditional system, the soil provides macro- and micronutrients for plants. Meanwhile, water helps dissolve the nutrients from the soil and provides plants with components needed for the complex biochemistry of photosynthesis. But in hydroponics, a nutrient solution is used to provide both hydration and nutrition.
As a result, hydroponics requires plants to use less energy to get much-needed nutrients. It also allows growers to customize concentration and types of nutrition provided for different plants and across their growing cycle. Plus it takes up less space than traditional growing methods and can be used in places where traditional farming just isn't possible -- like desserts.. or Mars!
There are 6 basic types of hydroponic growing, but for this project, we are focused on a wicking system. A wick of absorbable materials, such as string, rope or fabric is used to move the nutrient solution from a reservoir to the plants. And inert growing media is used to hold the solution and provide structure for the plant to grow. This kind of system is to easy to build, does not need pumps or moving parts, and is perfect for smaller plants that don't need a lot of intense watering or nutrition.
We're going to use and an upcycled water bottle to create our grower. Our wick will be a strip of cotton sock or felt. Store-bought nutrient concentrate and media will provide everything our lettuce seeds need.
UPDATE: Want to take it up a notch? Add a micro:bit controlled monitoring system to your hydroponics planter. Learn more at https://makershare.com/projects/using-microbit-monitor-hydroponics
First, we need to create our planter. To do that we'll modify a clean water bottle.
Start by measuring about 2 1/2 inches from the top of the bottle. Mark it. Use your scissors to cut the top from the bottle. The bottom of the bottle will be a reservoir for your nutrient solution. The top will hold the growing media and seeds.
Next, use the awl (or a Phillips head screwdriver) to pierce a hole in the center of the cap.
Now we need to make a wick for our planter. The easiest thing to do is to upcycle an old, unmatched washed cotton sock. If you don't have one an old towel or piece of felt will work. Use a sock made of natural fiber, as polyesters and nylons won't wick your nutrient solution well. Cut a strip from the sock that is between 1/2" to 1" wide. It doesn't have to be perfectly straight. Do not use the ribbed portion of the sock. The length should be approximately as long as the bottom section of the bottle.
Tie a knot in one end of the strip of fabric. Leave a tail. Pus the unknotted end through the hole you made in the cap so that the knot is on the inside of the cap. If needed, widen the hole to allow the strip to pass through, but take care not to widen it so much that the fabric falls out of the cap.
Place the cap back onto the neck of the water bottle.
(UPDATE: I now make a longer strip of sock and tie the knot so that there is a "tail" above and below. This extra length of wick goes into the groth media and helps to transport more liquid to the plant.)
Place some gravel in the bottom of the water bottle. This will help keep your planter from falling over, especially if you have pets. Small rocks or glass marbles also work. Make sure you clean and rinse the gravel well before adding it to the water bottle.
Mix your nutrient solution as described on the bottle. Usually, hydroponic nutrient solution will come as a liquid concentrate. One solution is a base, with potassium, phosphorous and nitrogen needed by all plants. You then supplement with a second solution for the type of plant you are growing -- flowers, vegetables, etc. Often you will make a dilute solution to start with and increase the concentration of nutrients as the plant grows.
Add the solution to the bottom of the bottle, your reservoir. Do not fill it all the way. Invert the top of the bottle and place on the reservoir, so that the wick hangs down into the nutrient solution. You may need to trim your wick.
Depending on your water and what you plan to grow, you may need to adjust the pH of your nutrient solution.
Fill the inverted top of the bottle with growing media, leaving some space between the top of the media and the rim of the bottle. Be sure that the tail from the knot of your wick extends into the growing media, to help wick the nutrients from below. Gently press it down.
For this project, you want something that is a mix of an inert material like coconut coir, perlite, or vermiculite, which will hold water and provide support for the plant. Grain or foam hydroponic media won't work for this project. Check your local gardening center or home improvement store for supplies.
For your seeds, there are many options. I recommend a pinch of lettuce seeds for classroom projects. They germinate quickly and easy to grow. You can try herbs, like dill or basil. Smaller flowers work nicely too. Cucumbers and tomatoes will work as well, though you may want to scale up to a 2-liter bottle planter. Bare-root strawberries can be grown in larger planters as well. Whatever you do, don't crowd your plants.
Once you've added your seeds, gently add sprinkle some of your nutrient solution over the growing media.
Because the nutrients in the solution can be degraded by light, cover the reservoir with aluminum foil. Then place a bit of plastic wrap (or a used, cleaned sandwich bag) over the top. Use rubber bands to hold the foil and wrap in place, if needed. The plastic creates a greenhouse effect, keeping the growing media warm and moist while the seeds germinate. Once the first green leaves appear, remove the wrap.
Place your planter in a sunny spot and let the seeds do their thing. Check the reservoir every week to make sure it doesn't run dry. Also check to make sure it isn't too wet, as that can cause roots to rot. For coconut coir and similar media, it should look somewhat dry on the surface, but release water when you pinch the soil. If your planter is getting too wet, reduce the width of your wick or try changing to a different material. Also, over time, wicks may transport less and less water, as minerals build up in the fabric. Replace your wick each time you replant.
As your plants grow, increase the concentration of nutrients according to the manufacturer's directions.
Then enjoy the veggies! To make a science experiment out of your planter, try starting lettuce seeds in traditional potting soil at the same time. Monitor how long it takes them to germinate in each, how quickly they grow (measuring the plants each day, for example) or how much water you use over their life.
Or skip the seeds completely! The ends of leaf lettuce heads, bunches of celery, onions and other "vegetable wastes" and be started in water, so why not give them a shot in your cool new planter.
So get started with hydroponics today, and you may some days have the skills to be a gardener on Mars.
If you enjoyed this project, check out my project "Using micro:bit to monitor hydroponics" as well.
And if you are looking for lots of fun, hands-on maker projects for your club, camp, school or library, please check out my book The Big Book of Maker Camp Projects (McGraw-Hill/TAB)