Hydroponics FAQ
What exactly is hydroponics?
How long has hydroponics been around?
I'm a scientist. Why should I care about hydroponics?
I'm a gardener. Why should I care about hydroponics?
I'm neither a scientist nor a gardener. Why should I care about hydroponics?
What exactly is hydroponics?
Hydroponics is the growing of plants in water instead of soil. To do this successfully, the water must be enriched with nutrients and sometimes oxygenated. Also, the plants must be placed in some type of inert medium like sand or Perlite (like we used) to anchor the roots.
How long has hydroponics been around?
I'm a scientist. Why should I care about hydroponics?
Scientists can use hydroponics to test how different nutrients affect a plant. With hydroponics, a scientist can measure exactly how much nutrient the plant is getting and can give the plant a deficiency or overabundance of a certain macro or micronutrient and determine precisely how it affects the plant's growth.
I'm a gardener. Why should I care about hydroponics?
Hydroponics can be very important to farmers and gardeners who want complete control over their plants. Many factors can affect plants that are grown in soil out in the fields. For a plant to receive a well balanced diet, everything in the soil must be in perfect balance. Rarely, if ever, can you find such ideal conditions in soil due to contamination and biological imbalances. But with hydroponics, water is enriched with these very same nutrient salts, creating a hydroponic nutrient solution that is perfectly balanced. And since this hydroponic nutrient solution is contained, it does not harm our environment as does runoff from fertilized soil. Also, very little water is lost to evaporation in a hydroponic system, making hydroponics very useful in drought stricken areas. Additionally, plants can be grown hydroponically inside greenhouses to protect them from pests; this makes harmful pesticides unnecessary.
I'm neither a scientist nor a gardener. Why should I care about hydroponics?
Even if you are neither a scientist nor a gardener, hydroponics can be important to you. There are so many benefits to hydroponics that it will probably become the agriculture of the future. Each day, more facts are learned about this type of farming, and soon we will know enough to make it the most efficient and effective way to grow plants. You too can benefit from the knowledge of hydroponics and could even start an amateur flower garden or vegetable garden from the information in our web page.
Lesson Three: Mix the Nutrient Solution
Step One: What nutrients do plants need?
All plants require certain chemical elements to live. These elements are known as essential nutrients, and they are divided into two categories: macronutrients, or nutrients plants need in large amounts; and micronutrients; nutrients plants need in small amounts. Macronutrients include carbon, hydrogen, oxygen, sulfur, phosphorus, nitrogen, potassium, calcium, and magnesium. Micronutrients include iron, copper, zinc, nickel, manganese, molybdenum, boron, and chlorine. These elements are used by plants in building biological molecules, as cofactors in enzymatic reactions, and in many other ways.
Plants obtain carbon and oxygen via the stomata in their leaves. However, they must absorb the other nutrients through their roots. This is where the hydroponic nutrient solution comes in: it supplies the plant with the nutrients it needs in the proper amounts.
Sources:
Campbell, Neil A., Jane B. Reece, and Lawrence G. Mitchell. "Plant Nutrition." Biology, Fifth Edition. Menlo Park, California: Benjamin/Cummings, 1999, pp. 714-717.
Poli, Dorothy Belle. "BSCI 442: Plant Physiology Lecture Outlines, Fall 99." http://www.life.umd.edu/classroom/BSCI442/lec6.html. Last visited: August, 2001.
Step Two: Figure out how much to make
One way to make a nutrient solution for hydroponics is to use the recipe proposed by Dr. Alan Cooper for a typical hydroponic system. This recipe makes 1000 liters of solution and consists of two parts concentrated in 10-Liter bottles. 10-Liter bottles may be hard to find, but you can alter the recipe to fit in 2-Liter soda bottles by dividing all the ingredients by five. Since this uses one-fifth the chemicals of the original, it only makes 200 L of solution. This may be more solution than you need. To figure out how much solution you need, multiply the number of plants you are going to grow by the number of days over which you are going to grow them. For example:
18 plants x 60 days = 1080 plant-days
Once you have the number of plant-days, divide 200 L by that amount to find liters of solution per plant per day:
200 L / 1080 plant-days = 0.185 L/plant/day = 185 mL/plant/day
While this may not seem like a lot, it is probably more than the plants need. It is hard to say how quickly plants actually use nutrients since the solution usually disappears from evaporation, but it is reasonable to expect that the plants use very little, especially if they are small plants. At this point you must make an educated guess based on the size of the plants. For instance, you might guess that radish plants will use no more than about 100 mL of solution per day. Accordingly, you would divide all the chemicals in the recipe by two in order to make about 92.6 mL/plant/day. It is not necessary to make exactly 100 mL since you guessed at that amount anyway.
The original mixing directions call for 100 mL of each of the two concentrated parts to be added for each 10 L of water. As with the concentrated chemicals, you can alter the mixing directions so the entire mixture fits in a 2-Liter bottle by dividing all the amounts by five. You would then use 20 mL of each concentrated part for each 2-Liter bottle of water. Note that if you scale the recipe for the concentrated solution to avoid making too much, you must scale the mixing directions accordingly. For example, since you used half as much chemical in the above example to make solution that is half as concentrated, you must use double the volume of each concentrated part per 2-Liter bottle of water so that the final concentration of nutrients is the same. In this example, you would use 40 mL of each part for each 2-Liter bottle of water.
Since the volume of each concentrated part used (40 mL) is of a much lesser magnitude than the volume of the water used (2 L = 2000 mL), one can make things easier by using 40 mL of each concentrated part and adding enough water to make 2 L of solution instead of adding 40 mL of each part to 2 L of water. Though this slightly alters the final concentration of the nutrient solution, it makes the entire mixture fit into a 2-Liter bottle, and the error is tolerable because this is not an exact science anyway.
For an experiment that involves changes in nutrient concentration, you will need to make more than one bottle of the concentrated part that contains the chemical that is your independent variable. To avoid wasting chemicals, you should recalculate the amount of chemical needed in each bottle if you are using the different solutions for different lengths of time or different numbers of plants. For example, if you make three bottles with different concentrations of magnesium sulfate and one bottle of EDTA iron and calcium nitrate for all the plants in your experiment, you will need one-third the amount of chemicals that you would otherwise need in each of the three bottles, but you will need the same amount of EDTA iron and calcium nitrate that you would otherwise need. It may be good to put some solutions in 1-Liter bottles if you don't need as much; be sure to calculate the correct volumes of those solutions to mix.
Source: "Hydro Juice." http://members.tripod.com/~busiweb/hydro/juice.htm. Last visited: August, 2001.
Step Three: Mixing the Chemicals
Materials needed:
all chemicals listed in recipe above
balance
filter paper or container to hold chemicals while measuring
two or more 2-Liter soda bottles, or other bottles with the recipe adjusted appropriately
chemical scoop
deionized water
small funnel
If you have all the chemicals in the recipe at hand in your chemistry lab, you should mix the concentrated solution in two parts: one with the calcium nitrate and EDTA iron, and one with all the rest of the chemicals.
Source: "Hydro Juice." http://members.tripod.com/~busiweb/hydro/juice.htm. Last visited: August, 2001.
Measure out the amount of each chemical you need on a balance with filter paper or a container to hold the chemicals, and mix the chemicals in clean 2-Liter soda bottles partially filled with deionized water. Be sure to use deionized water; tap water often contains ions that can mess up your solutions. You may need to use a small funnel to get the chemicals into the bottles without spilling them. Fill the bottles to the top with deionized water when all the chemicals have been added.
However, if you are missing any of the chemicals, you may have to make them yourself by reacting other chemicals. In that case it may be more practical to divide the concentrated solution into more than two parts.
Acid-Base Reactions
Use these directions to make some of the simpler compounds in the nutrient solution recipe using acids and bases.
EDTA Iron
Use these directions to make EDTA iron. EDTA iron is expensive to buy, but this recipe you can cook up in a chemistry lab seems to work pretty well. Do not try to substitute a simple iron compound in place of the EDTA iron. If you put a simple iron compound such as iron nitrate in your solution, it will form a precipitate with other chemicals in the solution such as phosphate. To avoid this, you must use chelated iron. A chelating agent is a molecule that grabs onto an ion such as iron and holds it tightly so that it cannot precipitate. However, plants still have ways of extracting the iron they need from these compounds. EDTA iron is one type of chelated iron that you can use in a nutrient solution.
Mixing Directions
Materials needed:
2-Liter clean empty mixing bottle
small funnel
graduated cylinder
Use the volume that you calculated before for each bottle of concentrated solution. Measure that volume of solution into the graduated cylinder using the funnel, and pour it into the mixing bottle, again using the funnel. Do this for each bottle in your recipe, and fill the mixing bottle to the top with deionized water when you are done. Again, be sure to use deionized water so that you do not introduce more chemicals into your nutrient solution. You now have a bottle of nutrient solution that is ready to feed to your plants!
Focus Questions
What essential nutrients do plants need to live?
What are macronutrients and micronutrients? Which essential nutrients are macro? Which are micro?
How do plants obtain their nutrients?
How do you figure out how much nutrient solution you need? How do you scale your recipe accordingly?
When you scale down the concentration of your nutrient solution, what must you do with the volume of nutrient solution you mix?
Why must you always use deionized water when you are mixing chemicals? What is wrong with tap water?
Why must you use EDTA iron in your nutrient solution? Why won't a simple iron compound work?
