Total-control Indoor Gardening with Modern Hydrop

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Start out with water that is as pure as possible. Surest is steam-distilled water available for about $1 a gallon at a pharmacy. But you'll have to change your nutrient water every week or two, and a 30-gallon reservoir can run through a lot of dollars and have you hauling around and recycling a lot of plastic water jugs.

Cheaper and more satisfying is to accumulate naturally pure rainwater in a well-rinsed and covered inert (foodgrade) plastic barrel connected to your roofs gutters. just be sure to rig a roof cleaning bypass for the first few gallons of each rain, so leaves won't get in to sink and decay on the bottom.

I'm fortunate enough to live on a hard rock mountain stream with no beaver ponds (to contribute cryptosporidium), people, or livestock ( E. coli or other pathogens) uphill, so, luckily for my plants, I share the water with the moose, bears, and brook trout. But I had it tested to be sure it was as pure as it looks.

Lake, stream, tap, or well water may be naturally saturated with minerals, including heavy metals that occur naturally in local rock, that make it unsuitable for a hydroponic system. Only a lab test can identify them properly.

Urban water supplies are always problematic. You'll recall from filling your aquarium that chlorine disinfectant (a gas that will kill plants) will dissipate naturally if water is boiled, strained through a filter of hay or straw, or just let sit for a day or two. Many cities add calcium carbonate to their water to raise PH to 8.0 and reduce pipe corrosion. This is ten times too alkaline for most plants.

An excess of minerals such as the calcium and carbon in the aforementioned example—each of them a nutrient that plants need in small quantity but that reduce nutrient-absorbing ability when in oversupply-can be harder to remove than chlorine; conventionally demineralized (softened) water contains too much common salt for best plant growth.

Red-brown or white crusty residue on porcelain plumbing appliances may be a clue that your own well water contains plant endangering levels of calcium, iron, sulfur, or other minerals.

Groundwater from low-lying streams, lakes, ponds, shallow wells, or seeps can be alive with small noxious creatures: bug eggs, germs and parasites, algaes and molds, seeds and spores that may be harmless in nature, where they belong, but that can multiply and wreak havoc in a hydroponic system.

Start with pure tested water.

Nutrients

Like most life on Earth, garden plants are mostly water. The 10% to 20% of a plant that is dry matter consists of about 45% (by weight) of both carbon (C) and oxygen (O) and 5% or 6% of the lightest element, hydrogen (H). Most of those elements go into the cellulose (C 6 H 10 O 5 ) that stiffens cell walls of stems, leaves, fruit, and root tissue. The plant absorbs these so-called free elements from the surrounding atmosphere and from water and atmospheric gasses in the soil. (Though the plant metabolizes CO 2 , not oxygen like animals, underground roots need a constant exposure to plenty of oxygen in order to absorb nutrients.)

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