Hydroponic growing techniques

Flower & Garden Magazine, Feb-March, 1993 by Brent Shepherd

HYDROPONICS HAS GAINED acceptance as a complement to traditional outdoor gardening and is taking gardening to places and people that before were restricted by space, time, climate and other uncontrollable factors. If you haven't already, you might consider joining the growing ranks of gardeners who are discovering the pleasures and benefits of growing their own vegetables year-round, indoors and out. Hydroponic vegetables grow faster, yield more, may cost less in the long run and often taste better than those you buy at the market. And they can do all these things without soil or sun.

Your hydroponic system can be as simple or complex as you want it to be. You can create your own device from basic supplies and your own intuition or invest in one of the many manufactured systems available on the market today. Any hydroponic system, whether homemade or manufactured, should do two things: support and aerate the root system of the plant and supply the plant with nutrients.

Soil is replaced by an aggregate that performs the support and aeration functions. The lighter and more porous it is, the better. Almost anything can serve as an aggregate, but some recommendations include lava stones and pea gravel. Both should be washed repeatedly before using to remove all excess dirt, dust and salt.

Another new product of note is rockwool, a sterile medium made from molten rock into which seeds may be planted. After germination the seedlings and rockwool may be transplanted directly into your system. It is relatively inexpensive and sold by many hydroponics manufacturers.

The nutrient solution primarily provides nitrogen, phosphorus and potassium, three elements crucial to plant growth. However, plants also need trace amounts of elements like sulphur, iron, manganese, zinc, copper, boron, magnesium, calcium, chlorine and molybdenum, which are normally provided by the soil. Consider getting your nutrient formula from a hydroponic specialist since many commercial formulas do not contain these trace elements.

Since plants require different nutrients at different stages of growth, it is best to provide a balanced solution at all times and let the plant use what it needs. Occasionally, water must be added to a system's reservoir to offset evaporation, but never add nutrient. Nutrient doesn't evaporate and you don't want a solution that's too strong. Always flush out the system with fresh water before introducing new nutrient solution.

Using distilled water for your solution is great if you can afford it, but tap water is generally sufficient, and it contains small amounts of the necessary trace elements. An analysis of your water supply is generally available upon request from your local water department, so you'll know just what your plants are getting. If your water supply is of poor quality, you might consider collecting rainwater.

Before adding nutrient, determine the pH of your water so necessary adjustments can be made, and check it periodically. Professional testing provides the most accurate results. Some manufacturers also sell indicator solution test kits, usually for less than $5.

In the pH range between 5.6 and 6.5, nutrients are most available to plants. The water supply in many areas has a pH between 7 and 8.2. To bring it down, add sulfuric acid, carefully following the directions on the label. Vinegar may also be used, but offers temporary results and must be repeated every few days.

The two most viable methods of getting the nutrient solution to and away from your plants are the flood-and-drain method and constant flow.

The simplest example of flood-and-drain involves gravity and a reservoir of solution connected to the aggregate by a feeding tube. Simply raise the reservoir above the aggregate to flood it. Place the reservoir below the aggregate to allow the solution to drain back into the reservoir. Enough residual solution is left behind in the aggregate to satisfy your plants and the drainage draws oxygen into the root zone. The drawback with flood-and-drain is that on non-automated systems it must be performed two or three times a day, which is all right for gardeners who stay close to home but not very practical for those who don't.

That's where the constant flow method comes in. A water pump is submerged in a reservoir of nutrient solution positioned beneath the aggregate. The pump sprays the root zone continually while solution drains back into the reservoir. If roots are submerged in the solution, a perforated tube attached to an air pump can provide a constant oxygen supply.

Another type of hydroponic system utilizes the "nutrient film technique," which forgoes the use of an aggregate and can use either the flood-and-drain or the constant flow method. Plants are supported by tubes or dark plastic sheets that keep the roots in complete darkness to stimulate their development. Inside the tube, most of the roots rest upon a thin, porous mat that slows the flow of the solution and distributes it more evenly.