11–14 Technician notes 1: Hydroponics
Land, water and bees – don’t
take us for granted: Hydroponics
Technician notes
The issue
The Earth’s resources are limited, but the human population is growing
fast. How can we ensure food security – adequate safe, healthy food –
for everyone?
As the demand for food increases, the demand for land and water to
grow it increases too. This investigation uses a simple do-it-yourself
hydroponics unit to explore how food plants can be grown in a small
space with limited water. It also enables students to investigate what
substances plants need to grow well. They can plan this study
themselves if desired.
Planning
If the plants are grown from seed as suggested here, you will have to germinate them in advance; for
radish or sorrel seeds, start them 1 week before the main lesson.
Each student or pair of students will need a small plastic drinks bottle, about 250–300 mL, with a wide neck.
Juice or smoothie bottles are suitable. You may need to start collecting these well in advance.
Students will set up a simple hydroponics unit made from a plastic drinks bottle, as described below. They
will use a nutrient solution in the base of the bottle and a growing medium as a soil substitute in the top
section, in which a seedling will be planted. The kit includes peat-mix plugs (from a regenerating source)
and radish or sorrel seeds, but the teacher may plan to use other media and other seeds, such as
sunflower or barley. Students will work in small groups to test the effect on the seedlings of varying the
nutrients in the solution. Again, if the class has more time, the teacher may introduce other variables to test,
such as the amount of light reaching the plants, temperature and pH.
As a low-demand alternative, students can simply investigate how growth and development of the
seedling takes place over a period of time, seeing how the root and shoots develop. They will also learn
that soil is not necessarily needed for healthy growth.
Safety
Technician carrying out preparation: Take care when using sharp instruments for cutting; clean up
all spillages immediately. Tape or sand sharp edges if you cut the bottles yourself.
Students: Take care when using sharp instruments; clean up all spillages immediately.
Wash hands after completing practical work.
If the seedlings are grown for eating, then preparation and growing conditions need to be clean and free from
biological or chemical contamination. This is not possible if the class is using a laboratory.
15
Technician notes
Investigation: plant growth and
hydroponics
11–14 Technician notes 1: Hydroponics
Equipment
From the kit:
● growing medium plugs in a tray (one per student/pair; 24 plugs in the tray)
● radish or sorrel seedlings (sprouted in advance from seeds in the kit)
● nutrient solutions (× 4: complete, and without K, P and N)
● litmus or universal indicator strips
● sodium bicarbonate (NaHCO3) (optional – depends on students’ planned investigation)
● vinegar (optional – depends on students’ planned investigation)
Technician notes
You will also need:
● small (250–300 mL), wide-necked plastic soft-drink bottles (one per student/pair)
● scissors/craft knives
● beakers
● labels
● opaque (black) paper or aluminium foil
● wicks made from strips of absorbent fabric (optional)
● pens and paper
● rulers
● tissue paper and parcel paper (optional – depends on students’ planned investigation)
● lamps (optional – depends on students’ planned investigation)
Preparation
1. Germinate the seeds in advance so that they are about 2 cm high on the
day of the practical. If the seeds provided in the kit are used, you should start
them about 1 week in advance. You will need one seedling per student or
pair, plus extras to cover accidental destruction.
2. The growing medium plugs (peat mix) are supplied in a tray, and need to
be soaked in lukewarm water before the seeds are planted. After soaking,
squeeze out excess water and then put one seed into each plug at a
depth of 3–5 mm. Cover the seeds with a small torn-off piece of growing
medium.
3. Leave the plugs in a warm place (24°C if possible) and keep them moist
but not wet for the seeds to germinate. Do not let the plugs dry out –
liquid should come to the surface of a plug when it is pressed down
lightly – but do not overwater them. The seedlings are ready if the roots
are clearly visible when you pick a plug from the tray.
4. Collect enough small (250–300 mL), wide-necked juice or smoothie bottles to
give one to each student or pair. If you are preparing the bottles in advance
yourself by cutting them open for the students, ensure that there are no
ragged or sharp edges left. The diagram shows how the top of the bottle is
cut off and will be inverted into the base section.
5. On the day before or the day of the practical, make up a complete nutrient
solution and other solutions lacking one nutrient in each case (phosphorus
–
P, potassium K and nitrate NO3) from distilled water
and the solutes
provided, following the instructions in the kit. You will need 300 mL solution
for each bottle unit used, to fill all the bottle units to the inverted neck, with
enough left over for topping up over the next few days. Make up equal
quantities of the four different solutions. Label the solutions with their
constituent minerals.
16
11–14 Technician notes 1: Hydroponics
6. If you provide the optional wick, make wicks from strips of absorbent
fabric.
7. If the seedlings are grown on in a warm place, the level of nutrient solution
in the bottle units may drop fast enough to require replacement over the
week or so that the investigation runs. Depending on whether and how
often students have access to the bottles, they may be responsible for
topping up the solutions, or it may fall to you. In either case, the spare
solutions and the bottle units must be clearly labelled so that the right
solution is poured into the right bottles.
Further information and variations
Seedlings
A propagator is useful in the production of seeds for this investigation. It
can be lined with absorbent paper and covered with its plastic lid to
encourage rapid germination of the selected seeds.
Growing medium
Students could make their own suggestions as an extension experiment, or
they could be given any of the following materials: shredded paper or fabric,
hay, gravel, sand, rockwool, perlite or coco fibre (coconut fibre used
commercially).
Nutrient solutions
For repeat experiments, you can purchase commercial hydroponic liquid and
dilute it according to instructions.
pH
The pH of the growing medium should be around pH 6; distilled water is
usually suitable. Students may wish to test this, so have litmus or universal
indicator strips ready. The pH of the nutrient liquid can be altered by
addition of sodium bicarbonate or vinegar if necessary.
Extension work might involve varying pH to look at its effect on plant growth.
Light and warmth
Extension activities could be designed to look at the effects of light and
warmth. Large sheets of translucent tissue paper or thick parcel paper may
be required if students wish to cut down the amount of light thatsome
seedlings receive. Depending on light conditions, students might need
lamps to provide suitable controlled lighting levels for their investigation.
Use a cool light source, such as a compact fluorescent tube (low-energy
light bulb). Other lamps also provide some warmth, which is a variable that
might be considered in this investigation.
Method
See the student activity sheet for a description.
17
Technician notes
The kit contains peat plugs from regenerating resources, which are fully
biodegradable, but other growing media are possible. If you repeat the
practical when the plugs of growing medium have been used up, germinate
the seeds on wet blotting paper or in cotton wool. This method ensures that
no nutrients have been used until the investigation begins.