This activity is part of the Backyard Biodiversity kit. This kit helps you explore the creatures and critters out near your cloths line and beyond.
What you will need
25 wheat or radish seeds, although any seeds will work. You may like to compare different seeds.
Cling film
Five small potting containers (polystyrene cups work well)
Potting mix
Normal water (from the tap)
Salt
Five one-litre (or bigger) container.
A marker pen
What to do
Sow your seeds
Label each of the containers with a solution number from 'Solution 1' to 'Solution 5'.
Fill each container with potting mix.
Place seven evenly spaced seeds into each container.
Wet the soil in each container with normal water, cover with cling film (take this off after germination) and put in a warm sunny place.
Grow the seedlings for about one week, until the second leaf is emerging if you use wheat or until the first true leaves (the first pair are germination leaves) for radish.
Make your salt solutions
Make the salt water solutions in five clean, empty bottles.
Label each of your containers 'Solution 1', 'Solution 2' etc
Make your solutions according to the chart below.
Amount of salt
in teaspoons
Amount of water
Solution 1
(normal water)
0 teaspoon
(0 grams)
1 litre
Solution 2
2/3 teaspoon
(3 grams)
1 litre
Solution 3
1 heaped teaspoon
(6 grams)
1 litre
Solution 4
2 level teaspoons
(15 grams)
1 litre
Solution 5
(sea water)
4 level teaspoons
(30 grams)
1 litre
After your plants have grown
When the plant has grown for a week or so, chose a leaf and measure its growth. If you are growing wheat, use the second leaf on each plant when it is about 50 millimetres long. Don't use the first leaf bec au se it only grows to 100 millimetres long.
Start watering each container with the corresponding salt solution.
Measure and record the length of the leaf before you put any solution on the plant, and then measure the same leaf every day after that. You will find a chart on our website to help you record these measurements. www.csiro.au/helix
Helpful hints
If you use table salt you will find that there is a residue that does not dissolve - it is the compound added to keep the salt dry.
Plant seven seeds and pull out the worst two, which are the two that emerge last, or not at all, so you are left with five good seedlings per container.
What's happening?
Salinity is a huge environmental problem in Australia. Dryland salinity, which is rising salt that damages soil, plants and buildings, is hard to comprehend and harder still to stop. Approximately 5.7 million hectares are at risk of, or affected by, dryland salinity. In 50 years it's estimated this area may increase to more than 17 million hectares.
In this experiment, some plants were grown with normal water. These plants should grow normally. You'll be able to tell if your experiment doesn't work if these plants die.
If you are growing wheat, they will grow from the base like other grasses. New cells are formed at the base of the plant and this pushes the tip along. The second leaf should grow about 30 millimetres per day, and reach a final length of about 150 millimetres. When you add salt water to the plant the growth rate of the leaves should decrease.
To see the results of the different solutions of salt water, you could make a graph that shows how fast the leaf grows in millimetres per day, and how badly the salt affects this. The results will be different for different plants, as some are naturally salt-tolerant like wheat.
Solution 1 should have no adverse effect on the plant and growth should be normal (30 millimetres per day).
Solution 2 will have only a small effect.
Solution 3 should have a bigger effect.
Solution 4 will cause growth to slow dramatically and nearly stop.
Solution 5 will kill the plant.
Plants absorb water from the soil through their roots by osmosis. Salinity is bad for osmosis and can even make the plant loose water back into the soil, making them look dry and wilted.
