| MadSci Network: Botany |
Complete question: I am about to be doing a project for my AP Biology class evaluating the effectiveness of hydroponic growing methods. I am planning on using both soilless culture and water culture setups, as well as a setup in potting soil as a control. I have read that beans are often used in hydroponics experiments, but I have not been able to find out why this is so. Also, I am concerned that bean plants will grow too large for my project; I am planning on growing them inside with plant lights for a minimum of 3 weeks, possibly longer. For this procedure, what plants would be best to use, and what are their optimum pH and other growing conditions? Also, I know that there are commercial nutrient solutions available for hydroponics, but I would like to know if it is possible to make your own. I found a recipe online, but it was incomplete; it simply lumped all the micronutrients as "trace elements." Thanks! Reply: Three weeks is a rather short timeframe for a plant growth experiment. Beans are readily available and germinate rapidly so are often used in school experiments. The drawbacks are that they need a lot of light, get tall, and often need staking. I often use houseplants because they root readily in solution culture and grow well under indoor light conditions. I particularly like piggyback plant (Tolmiea menziesii) because it roots readily via foliar plantlets. Devil's backbone (Kalanchoe daigremontianum) also produces foliar plantlets and works well. Wandering jews also root very easily and grow rapidly. If you want a crop, a leaf lettuce would be a good choice because it stays short, grows rapidly, does not need to flower before harvest, and is produced commercially in hydroponics. For most rapid growth, give your plants as much electric light as possible for 18 hours per day. A standard system for school experiments uses three, 4-foot shop fixtures side by side, each with two 40-watt cool white fluorescent tubes. Keep the plants within a couple cm of the tubes. It is often easier to buy a mixture of salts to make a hydroponic solution than to make up your own from individual salts because it requires balances, lab glassware, etc. One of that standard research nutrient solutions for hydroponics is Hoagland solution. Hoagland had two solutions, #1 has all nitrate; #2 had some ammonium, which kept the pH lower. Most people now use a modified Hoagland solution because the originals used iron tartrate instead of a chelate. I have never seen Hoagland solution sold commercially but have seen other research-type solutions offered by scientific supply companies at hefty prices ($7 per liter). Many hydroponic companies offer salt mixtures that can be used to prepare a hydroponic solution that will grow fine plants. They are relatively inexpensive with names such as Eco-Grow and Dyna-Gro. Try Worm's way (1-800-274-9676), Eco Enterprises (1-800-426-6937), or other hydroponic company. Miracle-Gro is not formulated for hydroponics so will kill plants if used in solution culture. Hoagland solution #1 (per liter of nutrient solution): 5 ml of 1 M potassium nitrate 5 ml of 1 M calcium nitrate 1 ml of 1 M monopotassium phosphate 2 ml of 1 M magnesium sulfate 1 ml of micronutrient stock solution (see recipe below) 1 to 5 ml of 1000 mg/liter iron from iron chelate (Fe-EDTA, Fe-DTPA, or Fe-EDDHA) Hoagland Solution #2: 6 ml of 1 M potassium nitrate 4 ml of 1 M calcium nitrate 1 ml of 1 M monoammonium phosphate 2 ml of 1 M magnesium sulfate 1 ml of micronutrient stock solution 1 to 5 ml of iron chelate stock solution as for #1 Micronutrient stock solution per liter: 2.86 g boric acid 1.81 g manganese chloride - 4 hydrate 0.22 g zinc sulfate - 7 hydrate 0.08 g copper sulfate - 5 hydrate 0.02 g 85% molybdic acid When diluted 1:1000 the micronutrient stock solution provides the following in mg/liter: Boron 0.5 Manganese 0.5 Zinc 0.05 Copper 0.02 Molybdenum 0.01 Reference Hershey, D.R. 1995. Plant Biology Science Projects. New York: Wiley.
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