Gardening for Primary Schools – suggestions for investigations

These suggestions for investigations help link your school garden to different topics in the curriculum. The RHS Campaign for School Gardening has lots of resources to help you get the most from your school garden.

Investigation G1: Is all the soil in the school grounds the same?

This group of tests can easily be carried out in the classroom. Collect samples of soil from a variety of places within the school grounds to use for the tests.

G1.1 Colour and appearance of fresh soil – Describe the fresh soil and record its colour by smearing a small amount onto a piece of white paper. When the smear is dry brush off the loose soil – a coloured stain is left behind.

Leave the soil samples to dry in the air and then carry out tests 2, 3 and 4 on each soil.

G1.2 Particle sizes – Fill a 50 cm3 (ml) beaker with soil and then pour the soil into a tall jar full of water. Give it a good shake and let it settle for 24 hours. The different sized particles in the soil settle out in layers with the heaviest ones at the bottom. Describe each layer and measure its thickness.

Soils vary in the proportion of different sized particles that make up the soil and this affects their texture. Clay soils have a lot of very tiny particles, which may not settle out even after 24 hours.

G1.3 Drainage through soil – Fold a filter paper into a cone and place it in a funnel. Put the funnel into a measuring cylinder (50 to 100 cm3). Take enough soil to half fill the funnel (make sure you use the same amount for each soil sample). Pour 25 cm3 of water slowly onto the soil and time how long it takes for the first drop of water to come through. If all the water soaks into the soil and nothing comes through, add another 25 cm3 of water.

This test measures how rapidly water drains through the soil. This is related to the texture – for example, water drains very slowly through clay soils. Ask the children to think how this could affect the watering of the plants.

G1.4 Acidity or alkalinity (pH) of soils – Find out the pH (acidity or alkalinity) of the soil by using a simple pH measuring kit (available from garden centres). Follow the instructions that come with the kit.

Many plants prefer a slightly acid soil (pH 5.5 to 6.5). In very acid soils (pH 3.5 to 4.5) or neutral to alkaline soils (pH 7 to 8) there may not be enough mineral salts available to plants. Digging compost into these soils is particularly helpful. Ask the children to think why this might be (see the gardening chart panel on composting).

Investigation G2: Do seeds need water to germinate?

This is a simple investigation in which you compare the germination of seeds with and without water. Download the Teacher guidance and Pupil sheets from the link on the right.

Investigation G3: What happens if the weeds are not taken out?

In the garden, take out weeds from half a row of radishes but not from the other half. Compare the size of the radishes that form. (You can measure the diameter or circumference of the radishes or you could even weigh them). The height of the plants would be another useful measure.

The weeds compete with the radishes for mineral salts, water and light and so the radishes are likely to be smaller. If very crowded, the plants may actually be taller because of their need to have enough light.

Investigation G4: What happens if seeds are not thinned?

Sow some seeds (e.g. radish) in film pots. Each pot should contain 3 seeds. After 5 days, in half the pots remove two of the seedlings and leave the rest of the pots unthinned. Let the radishes continue growing for 3 to 4 weeks and then compare the size of the radishes formed. Download the Teacher guidance and Pupil sheets from the link on the right.

This experiment shows that plants of the same species also compete with each other if they are too close together. Ask the children to think how they could investigate the effect of thinning out in the garden.

Investigation G5: How is water carried around the plant?

Place pieces of celery (leaf stalks) in coloured ink. The ink is carried in veins up to the leaf blades. Download the Teacher guidance from the link on the right.

Investigation G6: Do plants lose water?

Use a house plant or carry out the investigation on a plant in the school garden. Place a polythene bag over the leaf or shoot of the plant (but don’t detach the leaf from the plant). Leave the plant for at least 30 minutes and then examine the bag. The plant gives off water and this condenses in small droplets on the inside of the polythene bag. Download the Teacher guidance from the link on the right.

Investigation G7: What happens if you remove the tendrils from a pea plant?

Grow some sugar snap peas and give them a tent of twigs to scramble over. Remove the tendrils as they are formed from about half of the plants. Compare the growth of these plants with plants that still have tendrils. Click here for more information about sugar snap peas and how to grow them in the classroom.

Look at other plants growing around the school. How do they support themselves? They may, for example, have prickles (Bramble) or tiny hooks (Cleavers) for scrambling over plants. Honeysuckle uses its stems to twine round other plants whilst Traveller’s-joy (Clematis) uses its leaf stalks.

Investigation G8: Does adding mineral salts make a difference to the growth of radishes?

Grow radishes in film pots to which varying numbers of mineral salt pellets have been added. Compare the size of the radishes formed after 4 weeks. Download the Teacher guidance and Pupil sheets from the link on the right.

Investigation G9: What is eating my plants?

Carefully examine a plant (e.g. a lettuce), which is growing in the garden but shows signs of being eaten. Identify any animals found on the plant (use the Field studies Council fold out charts – ‘Woodland name trail’ and ‘Bugs on bushes’). [The links take you straight to the FSC Publications pages with details of these charts.] Some of the animals you find may just be resting on the plant and so you need to find out what each of these animals eat. You can then use this information to decide which animal (or animals) is most likely to be the culprit (eating the lettuce). Ask the children to construct a food chain involving this animal and the plant – e.g.

lettuce -> snail -> thrush -> sparrowhawk

Sometimes you may not find any animals. This suggests the culprit could be nocturnal and feeds only at night.