I have developed a type of hydrogarden pot similar to the ones sold for entirely too much money by gardening supply stores. Admittedly, my design is not as foolproof as the manufactured ones nor as eco-groovy as the 3-liter coke bottle ones.
Parts list:
- Two 32 oz clear plastic reynold's to-go cups
- A nail or drill
- Expanded clay pebbles
- 1/2" borer / hole saw [optional]
- A bit of 3/8" I.D. 1/2" O.D. PE or HDPE tubing (optional)
- Drinking straw (optional)
- Pliers (optional)
Method w/o using the optional stuff:
Poke or drill tiny holes in the bottom of one cup. Put growing medium and plant in cup with holes. Place cup with holes into cup without holes. Water/fertilize with 8-16 oz of solution. Periodically, lift the first cup to check the solution. When there is absolutely no more solution in the bottom cup (but before the medium dries), refill. Don't shove the top cup in, it should be gently placed back and allowed to sink to prevent the solution from spilling out of the sides.
With optional stuff:
Cut small notch at one end of tube so that if it is flush against something (bottom of cup), it does not seal. Drill 1/2" hole in plastic cup with holes. Put tube in 1/2" hole. Add plant and medium to cup with holes and place in cup without holes. Melt straw at one end by clasping with pliers and gently holding near heat source (I use a candle) in a well ventilated area (outside). Place straw in tube. Mark straw at top of tube. Fill cups with 8-16 oz solution. If the seal on the end of the straw is good, the straw should float. I grease the straw with horticultural oil to keep it from sticking to the walls of the tube as well, but this is optional. Mark the straw again at the top of the tube. The two marks now represent full and empty. When all of the solution is used up, the upper mark will be flush with the tube.
With either method, it is a good idea to stick panda film (black side in) to the bottom cup if the plant is going to be in an intensely lit environment. To do a better job of this, the unit can be placed into a regular pot and the top covered with panda film (with a hole for the plant of course). In indirect light situations, this is not needed.
I have personally given up on using the straw as a water level indicator.
The biggest issue is that the cups should not be filled with solution when the bottom cup is not empty. Keeping them filled with water results in very rapid root rot. I discovered this by leaving some outside.
For someone just starting out with hydroponics, this method is the easiest in my opinion. I have given succulents to people inside of these and come back to see them doing just fine months later. Organic hydro nutrients are highly compatible with passive hydroponics as well, so someone who balks at using hydroponics due to inorganic nutrients may appreciate this method as well.
For a hardcore hydroponic grower, this passive method is useful since many starts can be matured using cheap materials before the best specimens are put into an expensive system.
There is no need to buy a hundred pasta salads to get the cups. I bought these cups in a 500 pack for $60. Cash N' Carry and other places carrying restaurant supplies sell 50 packs for about $10.
Some people have commented that since these cups are made of polypropylene, the water becomes plasticized and contains xenoestrogens or some such badness. These are always the same people who use bug bombs, dip plants in miticide, buy conventional produce, eat McDonald's, and then try to talk to me about how hydroponics uses too many weird chemicals... so I'm not so worried about polypropylene.
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