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Indoor Garden 101

What Is Hydroponics?

The word hydroponics—from the Greek words "hydro" (water) and "ponos" (to work)—literally means "working water." In hydroponics, the water does the work because it brings all the necessary nutrients directly to the plant. (In soil, the plant has to do the work by developing an extensive root system to obtain its nutrients). Due to this difference, plants grow much faster in a hydroponic garden than in a soil garden, and they usually produce greater and more consistent yields in a smaller amount of space. Another major advantage to hydroponics is the reduced water usage: you use one tenth the water in hydroponics that you do in soil gardening, and your expended hydroponic nutrient solution can be recycled by pouring it on your house plants, garden, or lawn. Many indoor gardeners use a hydroponic system under a grow light, but the two things are not inseparable: a grow light will work great over an indoor soil garden, and you can place your hydroponic system on an outdoor porch or patio to enjoy the sun in the 'traditional' summer growing season.

Hydroponic Growth Media

By definition, a hydroponic medium should offer no nutritive value-its sole purpose is to provide support for the plant and to allow an even distribution of the nutrient solution. An ideal growing medium is sterile, inert, water- and nutrient-retentive, free-draining, non-toxic, and will promote vigorous root development.


Rockwool is the most revolutionary soilless medium to date. Horticultural Rockwool is made of volcanic basaltic rock and a binder which prevents potassium hydroxide and other elements from leaching into the nutrient solution. Rockwool provides 90-95 percent air space between its fibers. It is capable of holding more nutrient solution and more air than any other medium. When the Rockwool is completely saturated, it maintains a ratio of air to water which is ideal for promoting root development: 80 percent nutrient solution, 15 percent air space, and 5 percent Rockwool fibers.

Fired Clay Pellets

Fired Clay Pellets, often called grow rocks, are manufactured by heating clay pellets to very high temperatures, causing them to expand and puff up with air. Grow rocks retain moisture because they are porous, while the irregular shape and rough surface of the rocks promotes free drainage and air circulation. Grow rocks can also be reused from one crop to the next.


Perlite, or puffed sand, is a sterile and lightweight medium. It is a good medium for lettuce, cabbage, herbs, and other small crops. Its major drawback is its inability to give good support to the plants. It also tends to promote algae growth more than other media. Perlite is an excellent medium when used in grow bags or when combined with clay pellets in a reservoir or wick system. Perlite should be discarded after only one use.

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