Think you have to drop a load of cash to garden hydroponically? Think again. With a few old two-liter bottles, a large plastic tray, a little growing medium, and some nutrient solution, you can create your own passive hydroponics system. Add a couple of inexpensive modifications and you can convert that passive system into a continuously aerated one in no time.

To get started you'll need:

. a mixture of perlite and vermiculite

. a few clean two-liter bottles or other plastic growing containers

. a large plastic basin at least four inches tall

. hydroponic nutrient

. seeds

First, germinate a few of your seeds in a wet paper towel or Super Starter Plugs. Set aside in a warm place and make sure the seeds stay moist.

Next, cut about three inches off the top of your two-liter bottles, punch several small holes in the bottoms of each bottle, and set them inside your large basin. Mix your growing medium according to the specific needs of the plants you wish to grow. (While vermiculite retains moisture well, perlite allows for excellent drainage. As such, you might use two thirds perlite to one third vermiculite for spinach and other plants requiring well-draining growing conditions.) Whatever the ratio you choose, just be careful not to breathe any nuisance dust when working with these growing media.

Now add some of the growing medium to each bottle, nearly filling it to the top, mix a hydroponic nutrient such as Grow Big Liquid Plant Food or Dyna-Gro Liquid Grow per package directions, and pour some through each plant container to moisten your growing medium.

Once the seeds have sprouted, carefully transplant one seedling into each of your two-liter bottles. Next, fill the basin to about three inches with more of your nutrient solution. Although some of this solution will naturally evaporate, most will be wicked up through the holes in your plant pots, absorbed into the growing medium, and taken into the plants through their roots.

It won't be necessary to add more nutrient solution until the old solution is completely gone. As soon as you notice the bottom of the basin is dry, add another three inches of nutrient and simply repeat this watering cycle.

If you don't want to have to keep tabs on the nutrient solution so often, you might try converting this passive system to a continuously aerated one. You'll need an air stone, a bit of plastic tubing, and a small air pump. Just place the air stone in the bottom of the basin, connect it to the pump, and run the pump continuously to aerate your nutrient solution. Unlike the passive system, you'll want to make sure the nutrient solution level in your continuously aerated system remains topped off.

Plan to use the same growing medium and pots over a period of several months? In that case, it's a good idea to flush out excess nutrient salts about once a month. To do this, pour plain water into the tops of your containers, allow the water to leach through, and then dump the excess water that has collected in the basin.

Finally, place your hydroponics system in a sunny location and wait. If you don't think you are offering your plants enough sunlight, you can supplement them with a full-spectrum fluorescent fixture or HID lighting