Deep Water Culture
*Quick note: While possible, I don't recommend using smaller containers like jars DWC. A single, large reservoir supporting several or bigger plants makes for more effective use of the air pump. Pumps are physically limited in the number of tubes and stones they can support.
Begin with a clean five gallon bucket or tote that's been blacked out with paint, or is a dark enough plastic to limit light passing through to the inside. Too much light has the potential to damage roots and promote undesirable algae growth.
Containers made specifically for DWC can be purchased, but may be more expensive than systems you make yourself. If that's the route you take, you shouldn't need to drill any holes.
If you're making your own reservoir, cut holes in the containers lid using the hole saw. Drill a smaller hole in the lid or near the top of the side of the reservoir for the air pumps tubing to fit through. If the hole for the air tube is too low, it runs the risk of leaking nutrient solution. Pass the air tube through its hole and attach the stone. The tubing should be long enough the stone will be fully submerged in nutrient solution.
Before moving plants to the new system, fill it with nutrient solution and power on the submerged air stone. Adjust the flow of air according to the size of your reservoir. Take a moment to rest and watch as the glorious bubbles flowing through your res.
Once seedlings are tall enough to reach your light source from the inside of a net cup, carefully transfer them to an empty net cup, first cleaning their roots if your grow medium sticks to them. Add enough clay pebbles to the net cup the plant will be held in place and light wont pass through to the nutrient solution.
Set the net cup in the hole you drilled so the plants roots hang down into the nutrient solution. You'll want your container just full enough the roots are partially submerged. As the plant takes up water and nutrients and as the solution evaporates, its roots will grow along.
There can be too much oxygen coming through your air pump. An overly strong air flow rate can cause a number of issues in your nutrient solution, such as temperature regulation issues, and even potential toxicity.
As soon as your plants are suspended safe and sound over the container of nutrients, place the container in a sunny area, or under a grow light. Depending on the amount of shock the plant is experiencing, it can be best to be gentle on it until symptoms subside. If it is a plant that eventually requires full sun, maybe allow it a little extra time in the shade until it looks full strength.
Flush nutrient solution once in a while to prevent deficiencies. Monitor pH as necessary.
Roots will grow to be trapped in most net cups once they're large enough. Removing them from their cups may not be possible without permanently damaging one or both. If you're planning on moving your plants into a system where net cups may not make sense at some point, such as planting them in a coco-perlite mix, you may want to avoid putting them in net cups altogether.
One of the ideas I like comes from the video A Cheap Alternative to RockWool and Net Cups, posted by Hoocho on Youtube.
Best Plants To Grow: