We receive many requests for information on Science projects. Mostly the objective is to compare plants that are grown in hydroponics with the same plants under the same conditions, grown in soil.
Following are our suggestions for a simple and cheap way to have a hydroponic garden.
Please do note that hydroponics works really well because the gardener provides everything the plants need. So by cutting down to the very basic needs for a hydroponic system we actually give the plants a disadvantage.
- pH balance Rockwool
- Set up the system
- Plant the seeds
- Mix nutrients
- pH balance the solution
- Flood and Drain the plants
- Maintain your nutrient solution
- A remark on light
When doing a science project on hydroponics, these are the very basic things you need:
- A garden system
- growing medium
- A & B nutrient
- pH kit
- A bucket
- Piece of water hose, attached to the bucket and to your tray
With hydroponics the gardener usually also provides the light. If you have a grow light, use it. If you don’t make sure the plants get ample sunlight.
- A standard 2 part nursery tray and a bucket can be easily rigged to a ‘flood & drain’ garden.
- A hydroponics growing medium is completely inert. An inert medium will not effect the pH of the nutrient solution. It does not provide anything but an anchor for the plant. Hydroponic growing mediums are less compact than earth so the roots get more air.The growing medium we suggest for a project is ‘Rockwool’. Get one inch / 2.5 cm starter cubes.
- Any commercially prepared standard ‘hydroponic nutrient’ should do nicely. More information on nutrient ‘recipes’
- Plants will fail if their pH is too high or low. You need something to test the pH level of your nutrient solution and pH adjusters.
- Try an herb such as basil, it will grow and flower quickly. Leaf lettuce is another good plant to use because we harvest before it flowers. Stay away from tomato, pepper, cucumber because they take a very long time to fruit.
The first step is to pH balance the Rockwool starting cubes. pH refers to acid or alkaline level of the solution. The pH scale goes from one to fourteen, with seven being neutral. Any reading above seven is alkaline, any reading below seven is acidic. Tap water tends to be a little on the alkaline side and since plants prefer a slightly acidic root zone, we must add a little acid to the water we feed the plants.
Fill a one litre container with tap water. Pour about one tablespoon of the water into a small clear container. With an eye dropper add two drops of pH indicator solution to the water sample. Now compare the colour of the sample to the colour chart on the bottle. It will probably be greenish (pH 7-8). Next add two or three drops of ‘pH Down” (phosphoric acid) to the litre of water, stir and do the test again. Repeat this procedure until the sample turns yellow, indicating a pH of about 6.0. If the colour of the sample turns brownish or reddish, you have added too much pH Down, so just add more tap water to raise the pH level again. Be careful not to get any pH Down on your hands. If you do, wash immediately with water.
Put the garden in the place where it will remain. It is not easy to move when it is in use. Make sure the garden is on a sturdy, level surface where it can’t be knocked over. When mounting on a window ledge make sure the ledge is wider than the garden.
Rockwool must not sit on a flat surface, there must be an air space underneath. Prop up, use ½” of Perlite or a standard 2 part nursery tray.
Attach the hose to the tray and bucket.
Now you are ready to soak your one inch starter cubes in the pH balanced solution and put them on a plate or tray. It is now time to plant your seeds! Choose your seeds and insert one seed into the small hole in the top of each cube. If there is not a pre-made hole, make one about pencil width, a quarter inch / 0.75cm deep. Cover the hole with a bit of Rockwool so the seed has a dark place to sprout from. Take a small piece of saran wrap or plastic bag and cover the cubes to keep the moisture in. In a couple of days wet the cubes again with your pH balanced water.
Most seeds will begin to sprout in four to six days. Once they have sprouted, remove the saran wrap and moisten the cubes again.
The nutrients are the plant’s source of food so it is important that we do not give them too much or too little. The hydroponic nutrients supply all of the mineral elements that plants otherwise would get from the soil. Since your plants are still very young, mix the nutrient solution at half strength this time.
So use 2.5 ml of each the ‘A’ and ‘B’ nutrient per litre (Check the instructions on your nutrients.). Mix enough solution to fill your tray to ¾ rd of the height of the Rockwool cubes.
This process is identical to the procedure for preparing the seeding cubes. Always adjust the pH level after mixing the nutrients as they will also lower the pH a little.
Raise the bucket above the garden so the nutrient solution will flow into the tray.
The tray should be flooded to ¾ of the cubes’ height and drain immediately after. Make sure to not submerge the roots for more than 3 minutes.
Repeat this 2 to 3 times per day.
Plants use more water than nutrients, therefore top up the bucket with fresh water daily and pH balance the solution to 6.0 / 6.5.
Make a new solution each week. After the first week use ¾ strength nutrients, a week later you can start mixing a full strength solution.
This Flood and Drain technique exposes the roots directly to the nutrient solution. Erratic pH and EC (the amount of dissolved salts in the solution) is caused by the roots acting directly on the nutrient solution. Plants will benefit greatly by keeping these levels steady.
Remember that light is very important. If your plants don’t have light, it doesn’t matter what you give them. Read more about lighting.
TYPE OF ACTIVITY:
Two helpful references related to this project:
- Jones,L. (1977), Home hydroponics and how to do it! New York: Crown Publishers
- Nicol, E. (1990), “Hydroponics and Aquaculture in the High School Classroom” , The American Biology Teacher, Vol. 52 No.3 March 1990.
LESSON / ACTIVITY
The following are the details for constructing a hydroponic / aquaculture system for your classroom. I have used the apparatus for the past six years in my class with excellent results. A 100 gallon aquarium serves as our fish farm. Teams of students monitor the change in biomass of the fish population, (usually Tilapia).They also maintain records of the amount of high protein floating fish food consumed. As aquaculturist they try to develop a feeding regime that will maximize the fishes growth.
Water from this tank containing the fishes’ metabolic wastes is pumped every thirty minutes through a series of five hydroponic tubes filled with lava rock. Seedlings in Jiffy 7 peat pots are inserted into circular holes in the tubes. This soiless garden can support about forty plants.We have grown many varieties of lettuce, spinach, herbs, tomatoes, cucumbers, jalapeno peppers,as well as many types of flowers. In addition,climbing plants such as morning glories or four o’clocks or nasturtia are grown directly from the surface of the aquarium by inserting Jiffy 7 pots into floating styrofoam. These are supported so they arch across the ceiling.
Unless there is a need for a specific photoperiod, lights are left on for 24 hours. Growth is rapid in the system. A crop of leafy vegetables like spinach or soft leaved lettuce is ready for harvest in about four weeks. There is ample time to allow each student in each class to grow his or her own crop and perhaps time for some special individual projects at the end of the year. We usually celebrate the harvest with a pizza and salad party made from the classes own vegetables, of course. While in use the system can be used to visually demonstrate many important scientific principles from a variety of disciplines such as, animal and plant physiology, microbiology, and, of course, ecology.
The construction details are as follows. The hydroponic tubes are made from four inch diameter, thin walled drainage pipe. Each tube is five feet long and has circular holes 1-1/2 inches in diameter, cut every six inches with a keyhole saw. Jiffy 7 pots fit snugly into these holes. The tubes are filled with lightweight lava rock which provide excellent surface area for root support. Plastic pipe caps are glued to each end of the growing tubes . Inlet holes are drilled 1/4 inch from the bottom of each cap and tee shaped fittings are cemented into each hole.One half inch flexible tubing connects each tube to a submersible sump pump at the bottom of the aquarium. Overflow drainage holes are drilled 1/2 inch from the top edge of each cap. One inch diameter tees are cemented here and connected by plastic tubing. This returns any overflow to the tank.
A one-hour constant cycle timer activates the pump for approximately one minute, every half hour. When the timer goes off, the remaining solution will drain back through the pump through the fill line. A 24hour timer should turn the lights on and off at intervals that are appropriate for the plants being grown.
A thirty gallon aquarium or reservoir should be sufficient for this project. If you have a commercial plant growing rack, a pair of discarded aluminum crutches make a fine superstructure for light support.
Materials and Approximate Cost:
- 25 feet of thin walled plastic drainage pipe ($20)
- 10 feet of 1(one) inch diameter flexible plastic tubing ($10)
- 10 feet of 1/2-inch diameter flexible plastic tubing ($6)
- 6 plastic tees 1 inch diameter ($6)
- 6 plastic tees 1/2 inch diameter ($5)
- 2 tubes GOOP cement ($8)
- 1 submersible recirculating pump ($80)
- 8 boxes of lava rock ($40)
- 1(one) 24hour on/off appliance timer ($7)
- 1(one) 1hour constant cycling timer ($60)
- Total cost = $242